Merge remote-tracking branch 'eugenp/master'

.gitignore

@@ -43,3 +43,4 @@ spring-call-getters-using-reflection/.mvn/wrapper/maven-wrapper.properties
 spring-check-if-a-property-is-null/.mvn/wrapper/maven-wrapper.properties
 *.springBeans
 
+20171220-JMeter.csv

algorithms/src/main/java/com/baeldung/algorithms/maze/solver/BFSMazeSolver.java

@@ -0,0 +1,52 @@
+package com.baeldung.algorithms.maze.solver;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.List;
+
+public class BFSMazeSolver {
+    private static final int[][] DIRECTIONS = { { 0, 1 }, { 1, 0 }, { 0, -1 }, { -1, 0 } };
+
+    public List<Coordinate> solve(Maze maze) {
+        LinkedList<Coordinate> nextToVisit = new LinkedList<>();
+        Coordinate start = maze.getEntry();
+        nextToVisit.add(start);
+
+        while (!nextToVisit.isEmpty()) {
+            Coordinate cur = nextToVisit.remove();
+
+            if (!maze.isValidLocation(cur.getX(), cur.getY()) || maze.isExplored(cur.getX(), cur.getY())) {
+                continue;
+            }
+
+            if (maze.isWall(cur.getX(), cur.getY())) {
+                maze.setVisited(cur.getX(), cur.getY(), true);
+                continue;
+            }
+
+            if (maze.isExit(cur.getX(), cur.getY())) {
+                return backtrackPath(cur);
+            }
+
+            for (int[] direction : DIRECTIONS) {
+                Coordinate coordinate = new Coordinate(cur.getX() + direction[0], cur.getY() + direction[1], cur);
+                nextToVisit.add(coordinate);
+                maze.setVisited(cur.getX(), cur.getY(), true);
+            }
+        }
+        return Collections.emptyList();
+    }
+
+    private List<Coordinate> backtrackPath(Coordinate cur) {
+        List<Coordinate> path = new ArrayList<>();
+        Coordinate iter = cur;
+
+        while (iter != null) {
+            path.add(iter);
+            iter = iter.parent;
+        }
+
+        return path;
+    }
+}

algorithms/src/main/java/com/baeldung/algorithms/maze/solver/Coordinate.java

@@ -0,0 +1,31 @@
+package com.baeldung.algorithms.maze.solver;
+
+public class Coordinate {
+    int x;
+    int y;
+    Coordinate parent;
+
+    public Coordinate(int x, int y) {
+        this.x = x;
+        this.y = y;
+        this.parent = null;
+    }
+
+    public Coordinate(int x, int y, Coordinate parent) {
+        this.x = x;
+        this.y = y;
+        this.parent = parent;
+    }
+
+    int getX() {
+        return x;
+    }
+
+    int getY() {
+        return y;
+    }
+
+    Coordinate getParent() {
+        return parent;
+    }
+}

algorithms/src/main/java/com/baeldung/algorithms/maze/solver/DFSMazeSolver.java

@@ -0,0 +1,48 @@
+package com.baeldung.algorithms.maze.solver;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class DFSMazeSolver {
+    private static final int[][] DIRECTIONS = { { 0, 1 }, { 1, 0 }, { 0, -1 }, { -1, 0 } };
+
+    public List<Coordinate> solve(Maze maze) {
+        List<Coordinate> path = new ArrayList<>();
+        if (explore(maze, maze.getEntry()
+            .getX(),
+            maze.getEntry()
+                .getY(),
+            path)) {
+            return path;
+        }
+        return Collections.emptyList();
+    }
+
+    private boolean explore(Maze maze, int row, int col, List<Coordinate> path) {
+        if (!maze.isValidLocation(row, col) || maze.isWall(row, col) || maze.isExplored(row, col)) {
+            return false;
+        }
+
+        path.add(new Coordinate(row, col));
+        maze.setVisited(row, col, true);
+
+        if (maze.isExit(row, col)) {
+            return true;
+        }
+
+        for (int[] direction : DIRECTIONS) {
+            Coordinate coordinate = getNextCoordinate(row, col, direction[0], direction[1]);
+            if (explore(maze, coordinate.getX(), coordinate.getY(), path)) {
+                return true;
+            }
+        }
+
+        path.remove(path.size() - 1);
+        return false;
+    }
+
+    private Coordinate getNextCoordinate(int row, int col, int i, int j) {
+        return new Coordinate(row + i, col + j);
+    }
+}

algorithms/src/main/java/com/baeldung/algorithms/maze/solver/Maze.java

@@ -0,0 +1,141 @@
+package com.baeldung.algorithms.maze.solver;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Scanner;
+
+public class Maze {
+    private static final int ROAD = 0;
+    private static final int WALL = 1;
+    private static final int START = 2;
+    private static final int EXIT = 3;
+    private static final int PATH = 4;
+
+    private int[][] maze;
+    private boolean[][] visited;
+    private Coordinate start;
+    private Coordinate end;
+
+    public Maze(File maze) throws FileNotFoundException {
+        String fileText = "";
+        try (Scanner input = new Scanner(maze)) {
+            while (input.hasNextLine()) {
+                fileText += input.nextLine() + "\n";
+            }
+        }
+        initializeMaze(fileText);
+    }
+
+    private void initializeMaze(String text) {
+        if (text == null || (text = text.trim()).length() == 0) {
+            throw new IllegalArgumentException("empty lines data");
+        }
+
+        String[] lines = text.split("[\r]?\n");
+        maze = new int[lines.length][lines[0].length()];
+        visited = new boolean[lines.length][lines[0].length()];
+
+        for (int row = 0; row < getHeight(); row++) {
+            if (lines[row].length() != getWidth()) {
+                throw new IllegalArgumentException("line " + (row + 1) + " wrong length (was " + lines[row].length() + " but should be " + getWidth() + ")");
+            }
+
+            for (int col = 0; col < getWidth(); col++) {
+                if (lines[row].charAt(col) == '#')
+                    maze[row][col] = WALL;
+                else if (lines[row].charAt(col) == 'S') {
+                    maze[row][col] = START;
+                    start = new Coordinate(row, col);
+                } else if (lines[row].charAt(col) == 'E') {
+                    maze[row][col] = EXIT;
+                    end = new Coordinate(row, col);
+                } else
+                    maze[row][col] = ROAD;
+            }
+        }
+    }
+
+    public int getHeight() {
+        return maze.length;
+    }
+
+    public int getWidth() {
+        return maze[0].length;
+    }
+
+    public Coordinate getEntry() {
+        return start;
+    }
+
+    public Coordinate getExit() {
+        return end;
+    }
+
+    public boolean isExit(int x, int y) {
+        return x == end.getX() && y == end.getY();
+    }
+
+    public boolean isStart(int x, int y) {
+        return x == start.getX() && y == start.getY();
+    }
+
+    public boolean isExplored(int row, int col) {
+        return visited[row][col];
+    }
+
+    public boolean isWall(int row, int col) {
+        return maze[row][col] == WALL;
+    }
+
+    public void setVisited(int row, int col, boolean value) {
+        visited[row][col] = value;
+    }
+
+    public boolean isValidLocation(int row, int col) {
+        if (row < 0 || row >= getHeight() || col < 0 || col >= getWidth()) {
+            return false;
+        }
+        return true;
+    }
+
+    public void printPath(List<Coordinate> path) {
+        int[][] tempMaze = Arrays.stream(maze)
+            .map(int[]::clone)
+            .toArray(int[][]::new);
+        for (Coordinate coordinate : path) {
+            if (isStart(coordinate.getX(), coordinate.getY()) || isExit(coordinate.getX(), coordinate.getY())) {
+                continue;
+            }
+            tempMaze[coordinate.getX()][coordinate.getY()] = PATH;
+        }
+        System.out.println(toString(tempMaze));
+    }
+
+    public String toString(int[][] maze) {
+        StringBuilder result = new StringBuilder(getWidth() * (getHeight() + 1));
+        for (int row = 0; row < getHeight(); row++) {
+            for (int col = 0; col < getWidth(); col++) {
+                if (maze[row][col] == ROAD) {
+                    result.append(' ');
+                } else if (maze[row][col] == WALL) {
+                    result.append('#');
+                } else if (maze[row][col] == START) {
+                    result.append('S');
+                } else if (maze[row][col] == EXIT) {
+                    result.append('E');
+                } else {
+                    result.append('.');
+                }
+            }
+            result.append('\n');
+        }
+        return result.toString();
+    }
+
+    public void reset() {
+        for (int i = 0; i < visited.length; i++)
+            Arrays.fill(visited[i], false);
+    }
+}

algorithms/src/main/java/com/baeldung/algorithms/maze/solver/MazeDriver.java

@@ -0,0 +1,34 @@
+package com.baeldung.algorithms.maze.solver;
+
+import java.io.File;
+import java.util.List;
+
+public class MazeDriver {
+    public static void main(String[] args) throws Exception {
+        File maze1 = new File("src/main/resources/maze/maze1.txt");
+        File maze2 = new File("src/main/resources/maze/maze2.txt");
+
+        execute(maze1);
+        execute(maze2);
+    }
+
+    private static void execute(File file) throws Exception {
+        Maze maze = new Maze(file);
+        dfs(maze);
+        bfs(maze);
+    }
+
+    private static void bfs(Maze maze) {
+        BFSMazeSolver bfs = new BFSMazeSolver();
+        List<Coordinate> path = bfs.solve(maze);
+        maze.printPath(path);
+        maze.reset();
+    }
+
+    private static void dfs(Maze maze) {
+        DFSMazeSolver dfs = new DFSMazeSolver();
+        List<Coordinate> path = dfs.solve(maze);
+        maze.printPath(path);
+        maze.reset();
+    }
+}

algorithms/src/main/java/com/baeldung/algorithms/sudoku/BacktrackingAlgorithm.java

@@ -0,0 +1,104 @@
+package com.baeldung.algorithms.sudoku;
+
+import java.util.stream.IntStream;
+
+public class BacktrackingAlgorithm {
+
+    private static final int BOARD_SIZE = 9;
+    private static final int SUBSECTION_SIZE = 3;
+    private static final int BOARD_START_INDEX = 0;
+
+    private static final int NO_VALUE = 0;
+    private static final int MIN_VALUE = 1;
+    private static final int MAX_VALUE = 9;
+
+    private static int[][] board = {
+      {8, 0, 0, 0, 0, 0, 0, 0, 0},
+      {0, 0, 3, 6, 0, 0, 0, 0, 0},
+      {0, 7, 0, 0, 9, 0, 2, 0, 0},
+      {0, 5, 0, 0, 0, 7, 0, 0, 0},
+      {0, 0, 0, 0, 4, 5, 7, 0, 0},
+      {0, 0, 0, 1, 0, 0, 0, 3, 0},
+      {0, 0, 1, 0, 0, 0, 0, 6, 8},
+      {0, 0, 8, 5, 0, 0, 0, 1, 0},
+      {0, 9, 0, 0, 0, 0, 4, 0, 0}
+    };
+
+    public static void main(String[] args) {
+        BacktrackingAlgorithm solver = new BacktrackingAlgorithm();
+        solver.solve(board);
+        solver.printBoard();
+    }
+
+    private void printBoard() {
+        for (int row = BOARD_START_INDEX; row < BOARD_SIZE; row++) {
+            for (int column = BOARD_START_INDEX; column < BOARD_SIZE; column++) {
+                System.out.print(board[row][column] + " ");
+            }
+            System.out.println();
+        }
+    }
+
+    private boolean solve(int[][] board) {
+        for (int row = BOARD_START_INDEX; row < BOARD_SIZE; row++) {
+            for (int column = BOARD_START_INDEX; column < BOARD_SIZE; column++) {
+                if (board[row][column] == NO_VALUE) {
+                    for (int k = MIN_VALUE; k <= MAX_VALUE; k++) {
+                        board[row][column] = k;
+                        if (isValid(board, row, column) && solve(board)) {
+                            return true;
+                        }
+                        board[row][column] = NO_VALUE;
+                    }
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    private boolean isValid(int[][] board, int row, int column) {
+        return rowConstraint(board, row) &&
+          columnConstraint(board, column) &&
+          subsectionConstraint(board, row, column);
+    }
+
+    private boolean subsectionConstraint(int[][] board, int row, int column) {
+        boolean[] constraint = new boolean[BOARD_SIZE];
+        int subsectionRowStart = (row / SUBSECTION_SIZE) * SUBSECTION_SIZE;
+        int subsectionRowEnd = subsectionRowStart + SUBSECTION_SIZE;
+
+        int subsectionColumnStart = (column / SUBSECTION_SIZE) * SUBSECTION_SIZE;
+        int subsectionColumnEnd = subsectionColumnStart + SUBSECTION_SIZE;
+
+        for (int r = subsectionRowStart; r < subsectionRowEnd; r++) {
+            for (int c = subsectionColumnStart; c < subsectionColumnEnd; c++) {
+                if (!checkConstraint(board, r, constraint, c)) return false;
+            }
+        }
+        return true;
+    }
+
+    private boolean columnConstraint(int[][] board, int column) {
+        boolean[] constraint = new boolean[BOARD_SIZE];
+        return IntStream.range(BOARD_START_INDEX, BOARD_SIZE)
+          .allMatch(row -> checkConstraint(board, row, constraint, column));
+    }
+
+    private boolean rowConstraint(int[][] board, int row) {
+        boolean[] constraint = new boolean[BOARD_SIZE];
+        return IntStream.range(BOARD_START_INDEX, BOARD_SIZE)
+          .allMatch(column -> checkConstraint(board, row, constraint, column));
+    }
+
+    private boolean checkConstraint(int[][] board, int row, boolean[] constraint, int column) {
+        if (board[row][column] != NO_VALUE) {
+            if (!constraint[board[row][column] - 1]) {
+                constraint[board[row][column] - 1] = true;
+            } else {
+                return false;
+            }
+        }
+        return true;
+    }
+}

algorithms/src/main/java/com/baeldung/algorithms/sudoku/ColumnNode.java

@@ -0,0 +1,33 @@
+package com.baeldung.algorithms.sudoku;
+
+class ColumnNode extends DancingNode {
+    int size;
+    String name;
+
+    ColumnNode(String n) {
+        super();
+        size = 0;
+        name = n;
+        C = this;
+    }
+
+    void cover() {
+        unlinkLR();
+        for (DancingNode i = this.D; i != this; i = i.D) {
+            for (DancingNode j = i.R; j != i; j = j.R) {
+                j.unlinkUD();
+                j.C.size--;
+            }
+        }
+    }
+
+    void uncover() {
+        for (DancingNode i = this.U; i != this; i = i.U) {
+            for (DancingNode j = i.L; j != i; j = j.L) {
+                j.C.size++;
+                j.relinkUD();
+            }
+        }
+        relinkLR();
+    }
+}

algorithms/src/main/java/com/baeldung/algorithms/sudoku/DancingLinks.java

@@ -0,0 +1,133 @@
+package com.baeldung.algorithms.sudoku;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+
+public class DancingLinks {
+
+    private ColumnNode header;
+    private List<DancingNode> answer;
+
+    private void search(int k) {
+        if (header.R == header) {
+            handleSolution(answer);
+        } else {
+            ColumnNode c = selectColumnNodeHeuristic();
+            c.cover();
+
+            for (DancingNode r = c.D; r != c; r = r.D) {
+                answer.add(r);
+
+                for (DancingNode j = r.R; j != r; j = j.R) {
+                    j.C.cover();
+                }
+
+                search(k + 1);
+
+                r = answer.remove(answer.size() - 1);
+                c = r.C;
+
+                for (DancingNode j = r.L; j != r; j = j.L) {
+                    j.C.uncover();
+                }
+            }
+            c.uncover();
+        }
+    }
+
+    private ColumnNode selectColumnNodeHeuristic() {
+        int min = Integer.MAX_VALUE;
+        ColumnNode ret = null;
+        for (ColumnNode c = (ColumnNode) header.R; c != header; c = (ColumnNode) c.R) {
+            if (c.size < min) {
+                min = c.size;
+                ret = c;
+            }
+        }
+        return ret;
+    }
+
+    private ColumnNode makeDLXBoard(boolean[][] grid) {
+        final int COLS = grid[0].length;
+
+        ColumnNode headerNode = new ColumnNode("header");
+        List<ColumnNode> columnNodes = new ArrayList<>();
+
+        for (int i = 0; i < COLS; i++) {
+            ColumnNode n = new ColumnNode(Integer.toString(i));
+            columnNodes.add(n);
+            headerNode = (ColumnNode) headerNode.hookRight(n);
+        }
+        headerNode = headerNode.R.C;
+
+        for (boolean[] aGrid : grid) {
+            DancingNode prev = null;
+            for (int j = 0; j < COLS; j++) {
+                if (aGrid[j]) {
+                    ColumnNode col = columnNodes.get(j);
+                    DancingNode newNode = new DancingNode(col);
+                    if (prev == null)
+                        prev = newNode;
+                    col.U.hookDown(newNode);
+                    prev = prev.hookRight(newNode);
+                    col.size++;
+                }
+            }
+        }
+
+        headerNode.size = COLS;
+
+        return headerNode;
+    }
+
+    DancingLinks(boolean[][] cover) {
+        header = makeDLXBoard(cover);
+    }
+
+    public void runSolver() {
+        answer = new LinkedList<>();
+        search(0);
+    }
+
+    private void handleSolution(List<DancingNode> answer) {
+        int[][] result = parseBoard(answer);
+        printSolution(result);
+    }
+
+    private int size = 9;
+
+    private int[][] parseBoard(List<DancingNode> answer) {
+        int[][] result = new int[size][size];
+        for (DancingNode n : answer) {
+            DancingNode rcNode = n;
+            int min = Integer.parseInt(rcNode.C.name);
+            for (DancingNode tmp = n.R; tmp != n; tmp = tmp.R) {
+                int val = Integer.parseInt(tmp.C.name);
+                if (val < min) {
+                    min = val;
+                    rcNode = tmp;
+                }
+            }
+            int ans1 = Integer.parseInt(rcNode.C.name);
+            int ans2 = Integer.parseInt(rcNode.R.C.name);
+            int r = ans1 / size;
+            int c = ans1 % size;
+            int num = (ans2 % size) + 1;
+            result[r][c] = num;
+        }
+        return result;
+    }
+
+    private static void printSolution(int[][] result) {
+        int size = result.length;
+        for (int[] aResult : result) {
+            StringBuilder ret = new StringBuilder();
+            for (int j = 0; j < size; j++) {
+                ret.append(aResult[j]).append(" ");
+            }
+            System.out.println(ret);
+        }
+        System.out.println();
+    }
+}

algorithms/src/main/java/com/baeldung/algorithms/sudoku/DancingLinksAlgorithm.java

@@ -0,0 +1,121 @@
+package com.baeldung.algorithms.sudoku;
+
+import java.util.Arrays;
+
+public class DancingLinksAlgorithm {
+    private static final int BOARD_SIZE = 9;
+    private static final int SUBSECTION_SIZE = 3;
+    private static final int NO_VALUE = 0;
+    private static final int CONSTRAINTS = 4;
+    private static final int MIN_VALUE = 1;
+    private static final int MAX_VALUE = 9;
+    private static final int COVER_START_INDEX = 1;
+
+    private static int[][] board = {
+      {8, 0, 0, 0, 0, 0, 0, 0, 0},
+      {0, 0, 3, 6, 0, 0, 0, 0, 0},
+      {0, 7, 0, 0, 9, 0, 2, 0, 0},
+      {0, 5, 0, 0, 0, 7, 0, 0, 0},
+      {0, 0, 0, 0, 4, 5, 7, 0, 0},
+      {0, 0, 0, 1, 0, 0, 0, 3, 0},
+      {0, 0, 1, 0, 0, 0, 0, 6, 8},
+      {0, 0, 8, 5, 0, 0, 0, 1, 0},
+      {0, 9, 0, 0, 0, 0, 4, 0, 0}
+    };
+
+    public static void main(String[] args) {
+        DancingLinksAlgorithm solver = new DancingLinksAlgorithm();
+        solver.solve(board);
+    }
+
+    private void solve(int[][] board) {
+        boolean[][] cover = initializeExactCoverBoard(board);
+        DancingLinks dlx = new DancingLinks(cover);
+        dlx.runSolver();
+    }
+
+    private int getIndex(int row, int column, int num) {
+        return (row - 1) * BOARD_SIZE * BOARD_SIZE + (column - 1) * BOARD_SIZE + (num - 1);
+    }
+
+    private boolean[][] createExactCoverBoard() {
+        boolean[][] coverBoard = new boolean[BOARD_SIZE * BOARD_SIZE * MAX_VALUE][BOARD_SIZE * BOARD_SIZE * CONSTRAINTS];
+
+        int hBase = 0;
+        hBase = checkCellConstraint(coverBoard, hBase);
+        hBase = checkRowConstraint(coverBoard, hBase);
+        hBase = checkColumnConstraint(coverBoard, hBase);
+        checkSubsectionConstraint(coverBoard, hBase);
+        
+        return coverBoard;
+    }
+
+    private int checkSubsectionConstraint(boolean[][] coverBoard, int hBase) {
+        for (int row = COVER_START_INDEX; row <= BOARD_SIZE; row += SUBSECTION_SIZE) {
+            for (int column = COVER_START_INDEX; column <= BOARD_SIZE; column += SUBSECTION_SIZE) {
+                for (int n = COVER_START_INDEX; n <= BOARD_SIZE; n++, hBase++) {
+                    for (int rowDelta = 0; rowDelta < SUBSECTION_SIZE; rowDelta++) {
+                        for (int columnDelta = 0; columnDelta < SUBSECTION_SIZE; columnDelta++) {
+                            int index = getIndex(row + rowDelta, column + columnDelta, n);
+                            coverBoard[index][hBase] = true;
+                        }
+                    }
+                }
+            }
+        }
+        return hBase;
+    }
+
+    private int checkColumnConstraint(boolean[][] coverBoard, int hBase) {
+        for (int column = COVER_START_INDEX; column <= BOARD_SIZE; column++) {
+            for (int n = COVER_START_INDEX; n <= BOARD_SIZE; n++, hBase++) {
+                for (int row = COVER_START_INDEX; row <= BOARD_SIZE; row++) {
+                    int index = getIndex(row, column, n);
+                    coverBoard[index][hBase] = true;
+                }
+            }
+        }
+        return hBase;
+    }
+
+    private int checkRowConstraint(boolean[][] coverBoard, int hBase) {
+        for (int row = COVER_START_INDEX; row <= BOARD_SIZE; row++) {
+            for (int n = COVER_START_INDEX; n <= BOARD_SIZE; n++, hBase++) {
+                for (int column = COVER_START_INDEX; column <= BOARD_SIZE; column++) {
+                    int index = getIndex(row, column, n);
+                    coverBoard[index][hBase] = true;
+                }
+            }
+        }
+        return hBase;
+    }
+
+    private int checkCellConstraint(boolean[][] coverBoard, int hBase) {
+        for (int row = COVER_START_INDEX; row <= BOARD_SIZE; row++) {
+            for (int column = COVER_START_INDEX; column <= BOARD_SIZE; column++, hBase++) {
+                for (int n = COVER_START_INDEX; n <= BOARD_SIZE; n++) {
+                    int index = getIndex(row, column, n);
+                    coverBoard[index][hBase] = true;
+                }
+            }
+        }
+        return hBase;
+    }
+
+    private boolean[][] initializeExactCoverBoard(int[][] board) {
+        boolean[][] coverBoard = createExactCoverBoard();
+        for (int row = COVER_START_INDEX; row <= BOARD_SIZE; row++) {
+            for (int column = COVER_START_INDEX; column <= BOARD_SIZE; column++) {
+                int n = board[row - 1][column - 1];
+                if (n != NO_VALUE) {
+                    for (int num = MIN_VALUE; num <= MAX_VALUE; num++) {
+                        if (num != n) {
+                            Arrays.fill(coverBoard[getIndex(row, column, num)], false);
+                        }
+                    }
+                }
+            }
+        }
+        return coverBoard;
+    }
+}

algorithms/src/main/java/com/baeldung/algorithms/sudoku/DancingNode.java

@@ -0,0 +1,50 @@
+package com.baeldung.algorithms.sudoku;
+
+class DancingNode {
+    DancingNode L, R, U, D;
+    ColumnNode C;
+
+    DancingNode hookDown(DancingNode node) {
+        assert (this.C == node.C);
+        node.D = this.D;
+        node.D.U = node;
+        node.U = this;
+        this.D = node;
+        return node;
+    }
+
+    DancingNode hookRight(DancingNode node) {
+        node.R = this.R;
+        node.R.L = node;
+        node.L = this;
+        this.R = node;
+        return node;
+    }
+
+    void unlinkLR() {
+        this.L.R = this.R;
+        this.R.L = this.L;
+    }
+
+    void relinkLR() {
+        this.L.R = this.R.L = this;
+    }
+
+    void unlinkUD() {
+        this.U.D = this.D;
+        this.D.U = this.U;
+    }
+
+    void relinkUD() {
+        this.U.D = this.D.U = this;
+    }
+
+    DancingNode() {
+        L = R = U = D = this;
+    }
+
+    DancingNode(ColumnNode c) {
+        this();
+        C = c;
+    }
+}

algorithms/src/main/resources/maze/maze1.txt

@@ -0,0 +1,12 @@
+S ########
+#        #
+# ### ## #
+# #    # #
+# #  # # #
+# ## #####
+# #      #
+# # #  # #
+##### ####
+#   #    E
+# #    # #
+##########

algorithms/src/main/resources/maze/maze2.txt

@@ -0,0 +1,22 @@
+S ##########################
+# #      #                 #
+# # ####   ############### #
+# # #    # #               #
+# # #### # # ###############
+# # #    # # #             #
+# # # #### ### ########### #
+# # # #        #           #
+#       ################## #
+#########    # # #       # #
+# #       #### # ####### # #
+# # ### ###  # # #       # #
+#   #       ##   # ##### # #
+##### #######  # #     # # #
+#     #       ## ## #### # #
+# ##### #######     #      #
+#       #       ############
+####### #########        # #
+#       #         ######## #
+# ####### ###### ##   #    E
+#         #         #   ## #
+############################

core-java-8/src/test/java/com/baeldung/shufflingcollections/ShufflingCollectionsUnitTest.java

@@ -0,0 +1,70 @@
+package com.baeldung.shufflingcollections;
+
+import org.junit.Test;
+
+import java.util.*;
+import java.util.stream.Collectors;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ShufflingCollectionsUnitTest {
+
+    @Test
+    public void whenShufflingList_thenListIsShuffled() {
+        List<String> students = Arrays.asList("Foo", "Bar", "Baz", "Qux");
+
+        System.out.println("List before shuffling:");
+        System.out.println(students);
+
+        Collections.shuffle(students);
+        System.out.println("List after shuffling:");
+        System.out.println(students);
+    }
+
+    @Test
+    public void whenShufflingMapKeys_thenValuesAreShuffled() {
+        Map<Integer, String> studentsById = new HashMap<>();
+        studentsById.put(1, "Foo");
+        studentsById.put(2, "Bar");
+        studentsById.put(3, "Baz");
+        studentsById.put(4, "Qux");
+
+        System.out.println("Students before shuffling:");
+        System.out.println(studentsById.values());
+
+        List<Integer> shuffledStudentIds = new ArrayList<>(studentsById.keySet());
+        Collections.shuffle(shuffledStudentIds);
+
+        List<String> shuffledStudents = shuffledStudentIds.stream()
+          .map(id -> studentsById.get(id))
+          .collect(Collectors.toList());
+
+        System.out.println("Students after shuffling");
+        System.out.println(shuffledStudents);
+    }
+
+    @Test
+    public void whenShufflingSet_thenElementsAreShuffled() {
+        Set<String> students = new HashSet<>(Arrays.asList("Foo", "Bar", "Baz", "Qux"));
+
+        System.out.println("Set before shuffling:");
+        System.out.println(students);
+
+        List<String> studentList = new ArrayList<>(students);
+
+        Collections.shuffle(studentList);
+        System.out.println("Shuffled set elements:");
+        System.out.println(studentList);
+    }
+
+    @Test
+    public void whenShufflingWithSameRandomness_thenElementsAreShuffledDeterministically() {
+        List<String> students_1 = Arrays.asList("Foo", "Bar", "Baz", "Qux");
+        List<String> students_2 = Arrays.asList("Foo", "Bar", "Baz", "Qux");
+
+        Collections.shuffle(students_1, new Random(5));
+        Collections.shuffle(students_2, new Random(5));
+
+        assertThat(students_1).isEqualTo(students_2);
+    }
+}

core-java-9/src/test/java/com/baeldung/java9/httpclient/HttpClientTest.java

@@ -0,0 +1,218 @@
+package com.baeldung.java9.httpclient;
+
+import jdk.incubator.http.HttpClient;
+import jdk.incubator.http.HttpRequest;
+import jdk.incubator.http.HttpResponse;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.net.*;
+import java.util.Arrays;
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.stream.Collectors;
+
+import static org.hamcrest.CoreMatchers.containsString;
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.collection.IsEmptyCollection.empty;
+import static org.hamcrest.core.IsNot.not;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Created by adam.
+ */
+public class HttpClientTest {
+
+    @Test
+    public void shouldReturnSampleDataContentWhenConnectViaSystemProxy() throws IOException, InterruptedException, URISyntaxException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/post"))
+            .headers("Content-Type", "text/plain;charset=UTF-8")
+            .POST(HttpRequest.BodyProcessor.fromString("Sample body"))
+            .build();
+
+        HttpResponse<String> response = HttpClient.newBuilder()
+            .proxy(ProxySelector.getDefault())
+            .build()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+        assertThat(response.body(), containsString("Sample body"));
+    }
+
+    @Test
+    public void shouldNotFollowRedirectWhenSetToDefaultNever() throws IOException, InterruptedException, URISyntaxException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("http://stackoverflow.com"))
+            .version(HttpClient.Version.HTTP_1_1)
+            .GET()
+            .build();
+        HttpResponse<String> response = HttpClient.newBuilder()
+            .build()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_MOVED_PERM));
+        assertThat(response.body(), containsString("https://stackoverflow.com/"));
+    }
+
+    @Test
+    public void shouldFollowRedirectWhenSetToAlways() throws IOException, InterruptedException, URISyntaxException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("http://stackoverflow.com"))
+            .version(HttpClient.Version.HTTP_1_1)
+            .GET()
+            .build();
+        HttpResponse<String> response = HttpClient.newBuilder()
+            .followRedirects(HttpClient.Redirect.ALWAYS)
+            .build()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+        assertThat(response.finalRequest()
+            .uri()
+            .toString(), equalTo("https://stackoverflow.com/"));
+    }
+
+    @Test
+    public void shouldReturnOKStatusForAuthenticatedAccess() throws URISyntaxException, IOException, InterruptedException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/basic-auth"))
+            .GET()
+            .build();
+        HttpResponse<String> response = HttpClient.newBuilder()
+            .authenticator(new Authenticator() {
+                @Override
+                protected PasswordAuthentication getPasswordAuthentication() {
+                    return new PasswordAuthentication("postman", "password".toCharArray());
+                }
+            })
+            .build()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+    }
+
+    @Test
+    public void shouldSendRequestAsync() throws URISyntaxException, InterruptedException, ExecutionException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/post"))
+            .headers("Content-Type", "text/plain;charset=UTF-8")
+            .POST(HttpRequest.BodyProcessor.fromString("Sample body"))
+            .build();
+        CompletableFuture<HttpResponse<String>> response = HttpClient.newBuilder()
+            .build()
+            .sendAsync(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.get()
+            .statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+    }
+
+    @Test
+    public void shouldUseJustTwoThreadWhenProcessingSendAsyncRequest() throws URISyntaxException, InterruptedException, ExecutionException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/get"))
+            .GET()
+            .build();
+
+        ExecutorService executorService = Executors.newFixedThreadPool(2);
+
+        CompletableFuture<HttpResponse<String>> response1 = HttpClient.newBuilder()
+            .executor(executorService)
+            .build()
+            .sendAsync(request, HttpResponse.BodyHandler.asString());
+
+        CompletableFuture<HttpResponse<String>> response2 = HttpClient.newBuilder()
+            .executor(executorService)
+            .build()
+            .sendAsync(request, HttpResponse.BodyHandler.asString());
+
+        CompletableFuture<HttpResponse<String>> response3 = HttpClient.newBuilder()
+            .executor(executorService)
+            .build()
+            .sendAsync(request, HttpResponse.BodyHandler.asString());
+
+        CompletableFuture.allOf(response1, response2, response3)
+            .join();
+
+        assertThat(response1.get()
+            .statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+        assertThat(response2.get()
+            .statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+        assertThat(response3.get()
+            .statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+    }
+
+    @Test
+    public void shouldNotStoreCookieWhenPolicyAcceptNone() throws URISyntaxException, IOException, InterruptedException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/get"))
+            .GET()
+            .build();
+
+        HttpClient httpClient = HttpClient.newBuilder()
+            .cookieManager(new CookieManager(null, CookiePolicy.ACCEPT_NONE))
+            .build();
+
+        httpClient.send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(httpClient.cookieManager()
+            .get()
+            .getCookieStore()
+            .getCookies(), empty());
+    }
+
+    @Test
+    public void shouldStoreCookieWhenPolicyAcceptAll() throws URISyntaxException, IOException, InterruptedException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/get"))
+            .GET()
+            .build();
+
+        HttpClient httpClient = HttpClient.newBuilder()
+            .cookieManager(new CookieManager(null, CookiePolicy.ACCEPT_ALL))
+            .build();
+
+        httpClient.send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(httpClient.cookieManager()
+            .get()
+            .getCookieStore()
+            .getCookies(), not(empty()));
+    }
+
+    @Test
+    public void shouldProcessMultipleRequestViaStream() throws URISyntaxException, ExecutionException, InterruptedException {
+        List<URI> targets = Arrays.asList(new URI("https://postman-echo.com/get?foo1=bar1"), new URI("https://postman-echo.com/get?foo2=bar2"));
+
+        HttpClient client = HttpClient.newHttpClient();
+
+        List<CompletableFuture<String>> futures = targets.stream()
+            .map(target -> client.sendAsync(HttpRequest.newBuilder(target)
+                .GET()
+                .build(), HttpResponse.BodyHandler.asString())
+                .thenApply(response -> response.body()))
+            .collect(Collectors.toList());
+
+        CompletableFuture.allOf(futures.toArray(new CompletableFuture[0]))
+            .join();
+
+        if (futures.get(0)
+            .get()
+            .contains("foo1")) {
+            assertThat(futures.get(0)
+                .get(), containsString("bar1"));
+            assertThat(futures.get(1)
+                .get(), containsString("bar2"));
+        } else {
+            assertThat(futures.get(1)
+                .get(), containsString("bar2"));
+            assertThat(futures.get(1)
+                .get(), containsString("bar1"));
+        }
+
+    }
+
+}

core-java-9/src/test/java/com/baeldung/java9/httpclient/HttpRequestTest.java

@@ -0,0 +1,171 @@
+package com.baeldung.java9.httpclient;
+
+import jdk.incubator.http.HttpClient;
+import jdk.incubator.http.HttpRequest;
+import jdk.incubator.http.HttpResponse;
+import org.junit.Test;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.nio.file.Paths;
+import java.security.NoSuchAlgorithmException;
+import java.time.Duration;
+
+import static java.time.temporal.ChronoUnit.SECONDS;
+import static org.hamcrest.CoreMatchers.containsString;
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Created by adam.
+ */
+public class HttpRequestTest {
+
+    @Test
+    public void shouldReturnStatusOKWhenSendGetRequest() throws IOException, InterruptedException, URISyntaxException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/get"))
+            .GET()
+            .build();
+
+        HttpResponse<String> response = HttpClient.newHttpClient()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+    }
+
+    @Test
+    public void shouldUseHttp2WhenWebsiteUsesHttp2() throws IOException, InterruptedException, URISyntaxException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://stackoverflow.com"))
+            .version(HttpClient.Version.HTTP_2)
+            .GET()
+            .build();
+        HttpResponse<String> response = HttpClient.newHttpClient()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+        assertThat(response.version(), equalTo(HttpClient.Version.HTTP_2));
+    }
+
+    @Test
+    public void shouldFallbackToHttp1_1WhenWebsiteDoesNotUseHttp2() throws IOException, InterruptedException, URISyntaxException, NoSuchAlgorithmException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/get"))
+            .version(HttpClient.Version.HTTP_2)
+            .GET()
+            .build();
+
+        HttpResponse<String> response = HttpClient.newHttpClient()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.version(), equalTo(HttpClient.Version.HTTP_1_1));
+    }
+
+    @Test
+    public void shouldReturnStatusOKWhenSendGetRequestWithDummyHeaders() throws IOException, InterruptedException, URISyntaxException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/get"))
+            .headers("key1", "value1", "key2", "value2")
+            .GET()
+            .build();
+
+        HttpResponse<String> response = HttpClient.newHttpClient()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+    }
+
+    @Test
+    public void shouldReturnStatusOKWhenSendGetRequestTimeoutSet() throws IOException, InterruptedException, URISyntaxException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/get"))
+            .timeout(Duration.of(10, SECONDS))
+            .GET()
+            .build();
+
+        HttpResponse<String> response = HttpClient.newHttpClient()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+    }
+
+    @Test
+    public void shouldReturnNoContentWhenPostWithNoBody() throws IOException, InterruptedException, URISyntaxException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/post"))
+            .POST(HttpRequest.noBody())
+            .build();
+
+        HttpResponse<String> response = HttpClient.newHttpClient()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+    }
+
+    @Test
+    public void shouldReturnSampleDataContentWhenPostWithBodyText() throws IOException, InterruptedException, URISyntaxException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/post"))
+            .headers("Content-Type", "text/plain;charset=UTF-8")
+            .POST(HttpRequest.BodyProcessor.fromString("Sample request body"))
+            .build();
+
+        HttpResponse<String> response = HttpClient.newHttpClient()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+        assertThat(response.body(), containsString("Sample request body"));
+    }
+
+    @Test
+    public void shouldReturnSampleDataContentWhenPostWithInputStream() throws IOException, InterruptedException, URISyntaxException {
+        byte[] sampleData = "Sample request body".getBytes();
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/post"))
+            .headers("Content-Type", "text/plain;charset=UTF-8")
+            .POST(HttpRequest.BodyProcessor.fromInputStream(() -> new ByteArrayInputStream(sampleData)))
+            .build();
+
+        HttpResponse<String> response = HttpClient.newHttpClient()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+        assertThat(response.body(), containsString("Sample request body"));
+    }
+
+    @Test
+    public void shouldReturnSampleDataContentWhenPostWithByteArrayProcessorStream() throws IOException, InterruptedException, URISyntaxException {
+        byte[] sampleData = "Sample request body".getBytes();
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/post"))
+            .headers("Content-Type", "text/plain;charset=UTF-8")
+            .POST(HttpRequest.BodyProcessor.fromByteArray(sampleData))
+            .build();
+
+        HttpResponse<String> response = HttpClient.newHttpClient()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+        assertThat(response.body(), containsString("Sample request body"));
+    }
+
+    @Test
+    public void shouldReturnSampleDataContentWhenPostWithFileProcessorStream() throws IOException, InterruptedException, URISyntaxException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/post"))
+            .headers("Content-Type", "text/plain;charset=UTF-8")
+            .POST(HttpRequest.BodyProcessor.fromFile(Paths.get("src/test/resources/sample.txt")))
+            .build();
+
+        HttpResponse<String> response = HttpClient.newHttpClient()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+        assertThat(response.body(), containsString("Sample file content"));
+    }
+
+}

core-java-9/src/test/java/com/baeldung/java9/httpclient/HttpResponseTest.java

@@ -0,0 +1,55 @@
+package com.baeldung.java9.httpclient;
+
+import jdk.incubator.http.HttpClient;
+import jdk.incubator.http.HttpRequest;
+import jdk.incubator.http.HttpResponse;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.net.URI;
+import java.net.URISyntaxException;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.Matchers.isEmptyString;
+import static org.hamcrest.core.IsNot.not;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Created by adam.
+ */
+public class HttpResponseTest {
+
+    @Test
+    public void shouldReturnStatusOKWhenSendGetRequest() throws IOException, InterruptedException, URISyntaxException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("https://postman-echo.com/get"))
+            .GET()
+            .build();
+
+        HttpResponse<String> response = HttpClient.newHttpClient()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_OK));
+        assertThat(response.body(), not(isEmptyString()));
+    }
+
+    @Test
+    public void shouldResponseURIDifferentThanRequestUIRWhenRedirect() throws IOException, InterruptedException, URISyntaxException {
+        HttpRequest request = HttpRequest.newBuilder()
+            .uri(new URI("http://stackoverflow.com"))
+            .version(HttpClient.Version.HTTP_1_1)
+            .GET()
+            .build();
+        HttpResponse<String> response = HttpClient.newBuilder()
+            .followRedirects(HttpClient.Redirect.ALWAYS)
+            .build()
+            .send(request, HttpResponse.BodyHandler.asString());
+
+        assertThat(request.uri()
+            .toString(), equalTo("http://stackoverflow.com"));
+        assertThat(response.uri()
+            .toString(), equalTo("https://stackoverflow.com/"));
+    }
+
+}

core-java-9/src/test/java/com/baeldung/java9/httpclient/SimpleHttpRequestsUnitTest.java

@@ -1,126 +0,0 @@
-package com.baeldung.java9.httpclient;
-
-import static java.net.HttpURLConnection.HTTP_OK;
-import static org.junit.Assert.assertTrue;
-
-import java.io.IOException;
-import java.net.CookieManager;
-import java.net.CookiePolicy;
-import java.net.URI;
-import java.net.URISyntaxException;
-import java.net.http.HttpClient;
-import java.net.http.HttpHeaders;
-import java.net.http.HttpRequest;
-import java.net.http.HttpResponse;
-import java.security.NoSuchAlgorithmException;
-import java.util.List;
-import java.util.Map;
-import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.ExecutionException;
-
-import javax.net.ssl.SSLContext;
-import javax.net.ssl.SSLParameters;
-
-import org.junit.Before;
-import org.junit.Test;
-
-public class SimpleHttpRequestsUnitTest {
-
-    private URI httpURI;
-
-    @Before
-    public void init() throws URISyntaxException {
-        httpURI = new URI("http://www.baeldung.com/");
-    }
-
-    @Test
-    public void quickGet() throws IOException, InterruptedException, URISyntaxException {
-        HttpRequest request = HttpRequest.create(httpURI).GET();
-        HttpResponse response = request.response();
-        int responseStatusCode = response.statusCode();
-        String responseBody = response.body(HttpResponse.asString());
-        assertTrue("Get response status code is bigger then 400", responseStatusCode < 400);
-    }
-
-    @Test
-    public void asynchronousGet() throws URISyntaxException, IOException, InterruptedException, ExecutionException {
-        HttpRequest request = HttpRequest.create(httpURI).GET();
-        long before = System.currentTimeMillis();
-        CompletableFuture<HttpResponse> futureResponse = request.responseAsync();
-        futureResponse.thenAccept(response -> {
-            String responseBody = response.body(HttpResponse.asString());
-        });
-        HttpResponse resp = futureResponse.get();
-        HttpHeaders hs = resp.headers();
-        assertTrue("There should be more then 1 header.", hs.map().size() > 1);
-    }
-
-    @Test
-    public void postMehtod() throws URISyntaxException, IOException, InterruptedException {
-        HttpRequest.Builder requestBuilder = HttpRequest.create(httpURI);
-        requestBuilder.body(HttpRequest.fromString("param1=foo,param2=bar")).followRedirects(HttpClient.Redirect.SECURE);
-        HttpRequest request = requestBuilder.POST();
-        HttpResponse response = request.response();
-        int statusCode = response.statusCode();
-        assertTrue("HTTP return code", statusCode == HTTP_OK);
-    }
-
-    @Test
-    public void configureHttpClient() throws NoSuchAlgorithmException, URISyntaxException, IOException, InterruptedException {
-        CookieManager cManager = new CookieManager();
-        cManager.setCookiePolicy(CookiePolicy.ACCEPT_ORIGINAL_SERVER);
-
-        SSLParameters sslParam = new SSLParameters(new String[] { "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256" }, new String[] { "TLSv1.2" });
-
-        HttpClient.Builder hcBuilder = HttpClient.create();
-        hcBuilder.cookieManager(cManager).sslContext(SSLContext.getDefault()).sslParameters(sslParam);
-        HttpClient httpClient = hcBuilder.build();
-        HttpRequest.Builder reqBuilder = httpClient.request(new URI("https://www.facebook.com"));
-
-        HttpRequest request = reqBuilder.followRedirects(HttpClient.Redirect.ALWAYS).GET();
-        HttpResponse response = request.response();
-        int statusCode = response.statusCode();
-        assertTrue("HTTP return code", statusCode == HTTP_OK);
-    }
-
-    SSLParameters getDefaultSSLParameters() throws NoSuchAlgorithmException {
-        SSLParameters sslP1 = SSLContext.getDefault().getSupportedSSLParameters();
-        String[] proto = sslP1.getApplicationProtocols();
-        String[] cifers = sslP1.getCipherSuites();
-        System.out.println(printStringArr(proto));
-        System.out.println(printStringArr(cifers));
-        return sslP1;
-    }
-
-    String printStringArr(String... args) {
-        if (args == null) {
-            return null;
-        }
-        StringBuilder sb = new StringBuilder();
-        for (String s : args) {
-            sb.append(s);
-            sb.append("\n");
-        }
-        return sb.toString();
-    }
-
-    String printHeaders(HttpHeaders h) {
-        if (h == null) {
-            return null;
-        }
-
-        StringBuilder sb = new StringBuilder();
-        Map<String, List<String>> hMap = h.map();
-        for (String k : hMap.keySet()) {
-            sb.append(k).append(":");
-            List<String> l = hMap.get(k);
-            if (l != null) {
-                l.forEach(s -> {
-                    sb.append(s).append(",");
-                });
-            }
-            sb.append("\n");
-        }
-        return sb.toString();
-    }
-}

core-java-concurrency/src/main/java/com/baeldung/concurrent/prioritytaskexecution/Job.java

@@ -0,0 +1,25 @@
+package com.baeldung.concurrent.prioritytaskexecution;
+
+public class Job implements Runnable {
+    private String jobName;
+    private JobPriority jobPriority;
+    
+    public Job(String jobName, JobPriority jobPriority) {
+        this.jobName = jobName;
+        this.jobPriority = jobPriority != null ? jobPriority : JobPriority.MEDIUM;
+    }
+
+    public JobPriority getJobPriority() {
+        return jobPriority;
+    }
+
+    @Override
+    public void run() {
+        try {
+            System.out.println("Job:" + jobName + 
+              " Priority:" + jobPriority);
+            Thread.sleep(1000);
+        } catch (InterruptedException ignored) {
+        }
+    }
+}

core-java-concurrency/src/main/java/com/baeldung/concurrent/prioritytaskexecution/JobPriority.java

@@ -0,0 +1,7 @@
+package com.baeldung.concurrent.prioritytaskexecution;
+
+public enum JobPriority {
+    HIGH,
+    MEDIUM,
+    LOW
+}

core-java-concurrency/src/main/java/com/baeldung/concurrent/prioritytaskexecution/PriorityJobScheduler.java

@@ -0,0 +1,56 @@
+package com.baeldung.concurrent.prioritytaskexecution;
+
+import java.util.Comparator;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.PriorityBlockingQueue;
+import java.util.concurrent.TimeUnit;
+
+public class PriorityJobScheduler {
+
+    private ExecutorService priorityJobPoolExecutor;
+    private ExecutorService priorityJobScheduler = 
+      Executors.newSingleThreadExecutor();
+    private PriorityBlockingQueue<Job> priorityQueue;
+
+    public PriorityJobScheduler(Integer poolSize, Integer queueSize) {
+        priorityJobPoolExecutor = Executors.newFixedThreadPool(poolSize);
+        priorityQueue = new PriorityBlockingQueue<Job>(queueSize, 
+          Comparator.comparing(Job::getJobPriority));
+
+        priorityJobScheduler.execute(()->{
+            while (true) {
+                try {
+                    priorityJobPoolExecutor.execute(priorityQueue.take());
+                } catch (InterruptedException e) {
+                    // exception needs special handling
+                    break;
+                }
+            }
+        });
+    }
+
+    public void scheduleJob(Job job) {
+        priorityQueue.add(job);
+    }
+
+    public int getQueuedTaskCount() {
+        return priorityQueue.size();
+    }
+
+    protected void close(ExecutorService scheduler) {
+        scheduler.shutdown();
+        try {
+            if (!scheduler.awaitTermination(5, TimeUnit.SECONDS)) {
+                scheduler.shutdownNow();
+            }
+        } catch (InterruptedException e) {
+            scheduler.shutdownNow();
+        }
+    }
+
+    public void closeScheduler() {
+        close(priorityJobPoolExecutor);
+        close(priorityJobScheduler);
+    }
+}

core-java-concurrency/src/main/java/com/baeldung/concurrent/threadlifecycle/BlockedState.java

@@ -0,0 +1,31 @@
+package com.baeldung.concurrent.threadlifecycle;
+
+public class BlockedState {
+    public static void main(String[] args) throws InterruptedException {
+        Thread t1 = new Thread(new DemoThreadB());
+        Thread t2 = new Thread(new DemoThreadB());
+        
+        t1.start();
+        t2.start();
+        
+        Thread.sleep(1000);
+        
+        System.out.println(t2.getState());
+        System.exit(0);
+    }
+}
+
+class DemoThreadB implements Runnable {
+    @Override
+    public void run() {
+        commonResource();
+    }
+    
+    public static synchronized void commonResource() {
+        while(true) {
+            // Infinite loop to mimic heavy processing
+            // Thread 't1' won't leave this method
+            // when Thread 't2' enters this
+        }
+    }
+}

core-java-concurrency/src/main/java/com/baeldung/concurrent/threadlifecycle/NewState.java

@@ -0,0 +1,14 @@
+package com.baeldung.concurrent.threadlifecycle;
+
+public class NewState implements Runnable {
+    public static void main(String[] args) {
+        Runnable runnable = new NewState();
+        Thread t = new Thread(runnable);
+        System.out.println(t.getState());
+    }
+    
+    @Override
+    public void run() {
+        
+    }
+}

core-java-concurrency/src/main/java/com/baeldung/concurrent/threadlifecycle/RunnableState.java

@@ -0,0 +1,15 @@
+package com.baeldung.concurrent.threadlifecycle;
+
+public class RunnableState implements Runnable {
+    public static void main(String[] args) {
+        Runnable runnable = new NewState();
+        Thread t = new Thread(runnable);
+        t.start();
+        System.out.println(t.getState());
+    }
+    
+    @Override
+    public void run() {
+        
+    }
+}

core-java-concurrency/src/main/java/com/baeldung/concurrent/threadlifecycle/TerminatedState.java

@@ -0,0 +1,15 @@
+package com.baeldung.concurrent.threadlifecycle;
+
+public class TerminatedState implements Runnable {
+    public static void main(String[] args) throws InterruptedException {
+        Thread t1 = new Thread(new TerminatedState());
+        t1.start();
+        Thread.sleep(1000);
+        System.out.println(t1.getState());
+    }
+    
+    @Override
+    public void run() {
+        // No processing in this block
+    }
+}

core-java-concurrency/src/main/java/com/baeldung/concurrent/threadlifecycle/TimedWaitingState.java

@@ -0,0 +1,25 @@
+package com.baeldung.concurrent.threadlifecycle;
+
+public class TimedWaitingState {
+    public static void main(String[] args) throws InterruptedException {
+        DemoThread obj1 = new DemoThread();
+        Thread t1 = new Thread(obj1);
+        t1.start();
+        // The following sleep will give enough time for ThreadScheduler
+        // to start processing of thread t1
+        Thread.sleep(1000);
+        System.out.println(t1.getState());
+    }
+}
+
+class DemoThread implements Runnable {
+    @Override
+    public void run() {
+        try {
+            Thread.sleep(5000);
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            e.printStackTrace();
+        }
+    }
+}

core-java-concurrency/src/main/java/com/baeldung/concurrent/threadlifecycle/WaitingState.java

@@ -0,0 +1,35 @@
+package com.baeldung.concurrent.threadlifecycle;
+
+public class WaitingState implements Runnable {
+    public static Thread t1;
+
+    public static void main(String[] args) {
+        t1 = new Thread(new WaitingState());
+        t1.start();
+    }
+
+    public void run() {
+        Thread t2 = new Thread(new DemoThreadWS());
+        t2.start();
+
+        try {
+            t2.join();
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            e.printStackTrace();
+        }
+    }
+}
+
+class DemoThreadWS implements Runnable {
+    public void run() {
+        try {
+            Thread.sleep(1000);
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            e.printStackTrace();
+        }
+        
+        System.out.println(WaitingState.t1.getState());
+    }
+}

core-java-concurrency/src/main/java/com/baeldung/concurrent/waitandnotify/Data.java

@@ -1,7 +1,5 @@
 package com.baeldung.concurrent.waitandnotify;
 
-import org.slf4j.Logger;
-
 public class Data {
     private String packet;
     
@@ -14,6 +12,7 @@ public class Data {
             try {
                 wait();
             } catch (InterruptedException e) {
+                Thread.currentThread().interrupt(); 
                 System.out.println("Thread Interrupted");
             }
         }
@@ -28,6 +27,7 @@ public class Data {
             try { 
                 wait();
             } catch (InterruptedException e) {
+                Thread.currentThread().interrupt(); 
                 System.out.println("Thread Interrupted");
             }
         }

core-java-concurrency/src/main/java/com/baeldung/concurrent/waitandnotify/Receiver.java

@@ -20,6 +20,7 @@ public class Receiver implements Runnable {
             try {
                 Thread.sleep(ThreadLocalRandom.current().nextInt(1000, 5000));
             } catch (InterruptedException e) {
+                Thread.currentThread().interrupt(); 
                 System.out.println("Thread Interrupted");
             }
         }

core-java-concurrency/src/main/java/com/baeldung/concurrent/waitandnotify/Sender.java

@@ -25,6 +25,7 @@ public class Sender implements Runnable {
             try {
                 Thread.sleep(ThreadLocalRandom.current().nextInt(1000, 5000));
             } catch (InterruptedException e) {
+                Thread.currentThread().interrupt(); 
                 System.out.println("Thread Interrupted");
             }
         }