[BAEL-9555] - Created a core-java-modules folder

2019-05-05 17:22:09 +05:30
parent 8b63b0d90a
commit 3bae5e5334
1480 changed files with 25600 additions and 5594 deletions
@@ -0,0 +1,26 @@
+package com.baeldung.assertion;
+
+/**
+ * Simple demonstration of using Java assert keyword.
+ */
+public class Assertion {
+
+  public static void main(String[] args) {
+    Assertion assertion = new Assertion();
+    assertion.setup();
+  }
+
+  public void setup() {
+    Object conn = getConnection();
+    assert conn != null : "Connection is null";
+
+    // continue with other setup ...
+  }
+
+  // Simulate failure to get a connection; using Object
+  // to avoid dependencies on JDBC or some other heavy
+  // 3rd party library
+  public Object getConnection() {
+    return null;
+  }
+}
@@ -0,0 +1,23 @@
+package com.baeldung.binding;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Created by madhumita.g on 25-07-2018.
+ */
+public class Animal {
+
+    final static Logger logger = LoggerFactory.getLogger(Animal.class);
+
+    public void makeNoise() {
+        logger.info("generic animal noise");
+    }
+
+    public void makeNoise(Integer repetitions) {
+        while(repetitions != 0) {
+            logger.info("generic animal noise countdown " + repetitions);
+            repetitions -= 1;
+        }
+    }
+}
@@ -0,0 +1,43 @@
+package com.baeldung.binding;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Created by madhumita.g on 25-07-2018.
+ */
+public class AnimalActivity {
+
+    final static Logger logger = LoggerFactory.getLogger(AnimalActivity.class);
+
+
+    public static void sleep(Animal animal) {
+        logger.info("Animal is sleeping");
+    }
+
+    public static void sleep(Cat cat) {
+        logger.info("Cat is sleeping");
+    }
+
+    public static void main(String[] args) {
+
+        Animal animal = new Animal();
+
+        //calling methods of animal object
+        animal.makeNoise();
+
+        animal.makeNoise(3);
+
+
+        //assigning a dog object to reference of type Animal
+        Animal catAnimal = new Cat();
+
+        catAnimal.makeNoise();
+
+        // calling static function
+        AnimalActivity.sleep(catAnimal);
+
+        return;
+
+    }
+}
@@ -0,0 +1,18 @@
+package com.baeldung.binding;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Created by madhumita.g on 25-07-2018.
+ */
+public class Cat extends Animal {
+
+    final static Logger logger = LoggerFactory.getLogger(Cat.class);
+
+    public void makeNoise() {
+
+        logger.info("meow");
+    }
+
+}
@@ -0,0 +1,41 @@
+package com.baeldung.chainedexception;
+
+import com.baeldung.chainedexception.exceptions.GirlFriendOfManagerUpsetException;
+import com.baeldung.chainedexception.exceptions.ManagerUpsetException;
+import com.baeldung.chainedexception.exceptions.NoLeaveGrantedException;
+import com.baeldung.chainedexception.exceptions.TeamLeadUpsetException;
+
+public class LogWithChain {
+
+    public static void main(String[] args) throws Exception {
+        getLeave();
+    }
+
+    private static void getLeave() throws NoLeaveGrantedException {
+        try {
+            howIsTeamLead();
+        } catch (TeamLeadUpsetException e) {
+            throw new NoLeaveGrantedException("Leave not sanctioned.", e);
+        }
+    }
+
+    private static void howIsTeamLead() throws TeamLeadUpsetException {
+        try {
+            howIsManager();
+        } catch (ManagerUpsetException e) {
+            throw new TeamLeadUpsetException("Team lead is not in good mood", e);
+        }
+    }
+
+    private static void howIsManager() throws ManagerUpsetException {
+        try {
+            howIsGirlFriendOfManager();
+        } catch (GirlFriendOfManagerUpsetException e) {
+            throw new ManagerUpsetException("Manager is in bad mood", e);
+        }
+    }
+
+    private static void howIsGirlFriendOfManager() throws GirlFriendOfManagerUpsetException {
+        throw new GirlFriendOfManagerUpsetException("Girl friend of manager is in bad mood");
+    }
+}
@@ -0,0 +1,44 @@
+package com.baeldung.chainedexception;
+
+import com.baeldung.chainedexception.exceptions.GirlFriendOfManagerUpsetException;
+import com.baeldung.chainedexception.exceptions.ManagerUpsetException;
+import com.baeldung.chainedexception.exceptions.NoLeaveGrantedException;
+import com.baeldung.chainedexception.exceptions.TeamLeadUpsetException;
+
+public class LogWithoutChain {
+
+    public static void main(String[] args) throws Exception {
+        getLeave();
+    }
+
+    private static void getLeave() throws NoLeaveGrantedException {
+        try {
+            howIsTeamLead();
+        } catch (TeamLeadUpsetException e) {
+            e.printStackTrace();
+            throw new NoLeaveGrantedException("Leave not sanctioned.");
+        }
+    }
+
+    private static void howIsTeamLead() throws TeamLeadUpsetException {
+        try {
+            howIsManager();
+        } catch (ManagerUpsetException e) {
+            e.printStackTrace();
+            throw new TeamLeadUpsetException("Team lead is not in good mood");
+        }
+    }
+
+    private static void howIsManager() throws ManagerUpsetException {
+        try {
+            howIsGirlFriendOfManager();
+        } catch (GirlFriendOfManagerUpsetException e) {
+            e.printStackTrace();
+            throw new ManagerUpsetException("Manager is in bad mood");
+        }
+    }
+
+    private static void howIsGirlFriendOfManager() throws GirlFriendOfManagerUpsetException {
+        throw new GirlFriendOfManagerUpsetException("Girl friend of manager is in bad mood");
+    }
+}
@@ -0,0 +1,12 @@
+package com.baeldung.chainedexception.exceptions;
+
+public class GirlFriendOfManagerUpsetException extends Exception {
+
+    public GirlFriendOfManagerUpsetException(String message, Throwable cause) {
+        super(message, cause);
+    }
+
+    public GirlFriendOfManagerUpsetException(String message) {
+        super(message);
+    }
+}
@@ -0,0 +1,12 @@
+package com.baeldung.chainedexception.exceptions;
+
+public class ManagerUpsetException extends Exception {
+
+    public ManagerUpsetException(String message, Throwable cause) {
+        super(message, cause);
+    }
+
+    public ManagerUpsetException(String message) {
+        super(message);
+    }
+}
@@ -0,0 +1,12 @@
+package com.baeldung.chainedexception.exceptions;
+
+public class NoLeaveGrantedException extends Exception {
+
+    public NoLeaveGrantedException(String message, Throwable cause) {
+        super(message, cause);
+    }
+
+    public NoLeaveGrantedException(String message) {
+        super(message);
+    }
+}
@@ -0,0 +1,12 @@
+package com.baeldung.chainedexception.exceptions;
+
+public class TeamLeadUpsetException extends Exception {
+
+    public TeamLeadUpsetException(String message, Throwable cause) {
+        super(message, cause);
+    }
+
+    public TeamLeadUpsetException(String message) {
+        super(message);
+    }
+}
@@ -0,0 +1,9 @@
+package com.baeldung.className;
+
+public class RetrievingClassName {
+
+    public class InnerClass {
+
+    }
+
+}
@@ -0,0 +1,51 @@
+package com.baeldung.comparable;
+
+public class Player implements Comparable<Player> {
+
+    private int ranking;
+
+    private String name;
+
+    private int age;
+
+    public Player(int ranking, String name, int age) {
+        this.ranking = ranking;
+        this.name = name;
+        this.age = age;
+    }
+
+    public int getRanking() {
+        return ranking;
+    }
+
+    public void setRanking(int ranking) {
+        this.ranking = ranking;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public void setAge(int age) {
+        this.age = age;
+    }
+
+    @Override
+    public String toString() {
+        return this.name;
+    }
+
+    @Override
+    public int compareTo(Player otherPlayer) {
+        return (this.getRanking() - otherPlayer.getRanking());
+    }
+
+}
@@ -0,0 +1,25 @@
+package com.baeldung.comparable;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class PlayerSorter {
+
+    public static void main(String[] args) {
+
+        List<Player> footballTeam = new ArrayList<Player>();
+        Player player1 = new Player(59, "John", 20);
+        Player player2 = new Player(67, "Roger", 22);
+        Player player3 = new Player(45, "Steven", 24);
+        footballTeam.add(player1);
+        footballTeam.add(player2);
+        footballTeam.add(player3);
+
+        System.out.println("Before Sorting : " + footballTeam);
+        Collections.sort(footballTeam);
+        System.out.println("After Sorting : " + footballTeam);
+
+    }
+
+}
@@ -0,0 +1,46 @@
+package com.baeldung.comparator;
+
+public class Player {
+
+    private int ranking;
+
+    private String name;
+
+    private int age;
+
+    public Player(int ranking, String name, int age) {
+        this.ranking = ranking;
+        this.name = name;
+        this.age = age;
+    }
+
+    public int getRanking() {
+        return ranking;
+    }
+
+    public void setRanking(int ranking) {
+        this.ranking = ranking;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public void setAge(int age) {
+        this.age = age;
+    }
+
+    @Override
+    public String toString() {
+        return this.name;
+    }
+
+}
@@ -0,0 +1,12 @@
+package com.baeldung.comparator;
+
+import java.util.Comparator;
+
+public class PlayerAgeComparator implements Comparator<Player> {
+
+    @Override
+    public int compare(Player firstPlayer, Player secondPlayer) {
+       return (firstPlayer.getAge() - secondPlayer.getAge());
+    }
+
+}
@@ -0,0 +1,27 @@
+package com.baeldung.comparator;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class PlayerAgeSorter {
+
+    public static void main(String[] args) {
+        
+        List<Player> footballTeam = new ArrayList<Player>();
+        Player player1 = new Player(59, "John", 22);
+        Player player2 = new Player(67, "Roger", 20);
+        Player player3 = new Player(45, "Steven", 24);
+        footballTeam.add(player1);
+        footballTeam.add(player2);
+        footballTeam.add(player3);
+        
+        System.out.println("Before Sorting : " + footballTeam);
+        //Instance of PlayerAgeComparator
+        PlayerAgeComparator playerComparator = new PlayerAgeComparator();
+        Collections.sort(footballTeam, playerComparator);
+        System.out.println("After Sorting by age : " + footballTeam);
+        
+    }
+
+}
@@ -0,0 +1,12 @@
+package com.baeldung.comparator;
+
+import java.util.Comparator;
+
+public class PlayerRankingComparator implements Comparator<Player> {
+
+    @Override
+    public int compare(Player firstPlayer, Player secondPlayer) {
+       return (firstPlayer.getRanking() - secondPlayer.getRanking());
+    }
+
+}
@@ -0,0 +1,27 @@
+package com.baeldung.comparator;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class PlayerRankingSorter {
+
+    public static void main(String[] args) {
+        
+        List<Player> footballTeam = new ArrayList<Player>();
+        Player player1 = new Player(59, "John", 22);
+        Player player2 = new Player(67, "Roger", 20);
+        Player player3 = new Player(45, "Steven", 40);
+        footballTeam.add(player1);
+        footballTeam.add(player2);
+        footballTeam.add(player3);
+        
+        System.out.println("Before Sorting : " + footballTeam);
+        //Instance of PlayerRankingComparator
+        PlayerRankingComparator playerComparator = new PlayerRankingComparator();
+        Collections.sort(footballTeam, playerComparator);
+        System.out.println("After Sorting by ranking : " + footballTeam);
+        
+    }
+
+}
@@ -0,0 +1,68 @@
+package com.baeldung.controlstructures;
+
+public class ConditionalBranches {
+
+    /**
+     * Multiple if/else/else if statements examples. Shows different syntax usage.
+     */
+    public static void ifElseStatementsExamples() {
+        int count = 2; // Initial count value.
+
+        // Basic syntax. Only one statement follows. No brace usage.
+        if (count > 1)
+            System.out.println("Count is higher than 1");
+
+        // Basic syntax. More than one statement can be included. Braces are used (recommended syntax).
+        if (count > 1) {
+            System.out.println("Count is higher than 1");
+            System.out.println("Count is equal to: " + count);
+        }
+
+        // If/Else syntax. Two different courses of action can be included.
+        if (count > 2) {
+            System.out.println("Count is higher than 2");
+        } else {
+            System.out.println("Count is lower or equal than 2");
+        }
+
+        // If/Else/Else If syntax. Three or more courses of action can be included.
+        if (count > 2) {
+            System.out.println("Count is higher than 2");
+        } else if (count <= 0) {
+            System.out.println("Count is less or equal than zero");
+        } else {
+            System.out.println("Count is either equal to one, or two");
+        }
+    }
+
+    /**
+     * Ternary Operator example.
+     * @see ConditionalBranches#ifElseStatementsExamples()
+     */
+    public static void ternaryExample() {
+        int count = 2;
+        System.out.println(count > 2 ? "Count is higher than 2" : "Count is lower or equal than 2");
+    }
+
+    /**
+     * Switch structure example. Shows how to replace multiple if/else statements with one structure.
+     */
+    public static void switchExample() {
+        int count = 3;
+        switch (count) {
+        case 0:
+            System.out.println("Count is equal to 0");
+            break;
+        case 1:
+            System.out.println("Count is equal to 1");
+            break;
+        case 2:
+            System.out.println("Count is equal to 2");
+            break;
+        default:
+            System.out.println("Count is either negative, or higher than 2");
+            break;
+        }
+    }
+
+}
@@ -0,0 +1,157 @@
+package com.baeldung.controlstructures;
+
+public class Loops {
+
+    /**
+     * Dummy method. Only prints a generic message.
+     */
+    private static void methodToRepeat() {
+        System.out.println("Dummy method.");
+    }
+
+    /**
+     * Shows how to iterate 50 times with 3 different method/control structures.
+     */
+    public static void repetitionTo50Examples() {
+        for (int i = 1; i <= 50; i++) {
+            methodToRepeat();
+        }
+
+        int whileCounter = 1;
+        while (whileCounter <= 50) {
+            methodToRepeat();
+            whileCounter++;
+        }
+
+        int count = 1;
+        do {
+            methodToRepeat();
+            count++;
+        } while (count < 50);
+    }
+
+    /**
+     * Splits a sentence in words, and prints each word in a new line.
+     * @param sentence Sentence to print as independent words.
+     */
+    public static void printWordByWord(String sentence) {
+        for (String word : sentence.split(" ")) {
+            System.out.println(word);
+        }
+    }
+
+    /**
+     * Prints text an N amount of times. Shows usage of the {@code break} branching statement.
+     * @param textToPrint Text to repeatedly print.
+     * @param times Amount to times to print received text.
+     */
+    public static void printTextNTimes(String textToPrint, int times) {
+        int counter = 1;
+        while (true) {
+            System.out.println(textToPrint);
+            if (counter == times) {
+                break;
+            }
+        }
+    }
+
+    /**
+     * Prints text an N amount of times, up to 50. Shows usage of the {@code break} branching statement.
+     * @param textToPrint Text to repeatedly print.
+     * @param times Amount to times to print received text. If times is higher than 50, textToPrint will only be printed 50 times.
+     */
+    public static void printTextNTimesUpTo50(String textToPrint, int times) {
+        int counter = 1;
+        while (counter < 50) {
+            System.out.println(textToPrint);
+            if (counter == times) {
+                break;
+            }
+        }
+    }
+
+    /**
+     * Finds the index of {@code name} in a list
+     * @param name The name to look for
+     * @param names The list of names
+     * @return The index where the name was found or -1 otherwise
+     */
+    public static int findFirstInstanceOfName(String name, String[] names) {
+        int index = 0;
+        for ( ; index < names.length; index++) {
+            if (names[index].equals(name)) {
+                break;
+            }
+        }
+        return index == names.length ? -1 : index;
+    }
+
+    /**
+     * Takes several names and makes a list, skipping the specified {@code name}.
+     *
+     * @param name The name to skip
+     * @param names The list of names
+     * @return The list of names as a single string, missing the specified {@code name}.
+     */
+    public static String makeListSkippingName(String name, String[] names) {
+        String list = "";
+        for (int i = 0; i < names.length; i++) {
+            if (names[i].equals(name)) {
+                continue;
+            }
+            list += names[i];
+        }
+        return list;
+    }
+
+    /**
+     * Prints an specified amount of even numbers. Shows usage of both {@code break} and {@code continue} branching statements.
+     * @param amountToPrint Amount of even numbers to print.
+     */
+    public static void printEvenNumbers(int amountToPrint) {
+        if (amountToPrint <= 0) { // Invalid input
+            return;
+        }
+        int iterator = 0;
+        int amountPrinted = 0;
+        while (true) {
+            if (iterator % 2 == 0) { // Is an even number
+                System.out.println(iterator);
+                amountPrinted++;
+                iterator++;
+            } else {
+                iterator++;
+                continue; // Won't print
+            }
+            if (amountPrinted == amountToPrint) {
+                break;
+            }
+        }
+    }
+
+    /**
+     * Prints an specified amount of even numbers, up to 100. Shows usage of both {@code break} and {@code continue} branching statements.
+     * @param amountToPrint Amount of even numbers to print.
+     */
+    public static void printEvenNumbersToAMaxOf100(int amountToPrint) {
+        if (amountToPrint <= 0) { // Invalid input
+            return;
+        }
+        int iterator = 0;
+        int amountPrinted = 0;
+        while (amountPrinted < 100) {
+            if (iterator % 2 == 0) { // Is an even number
+                System.out.println(iterator);
+                amountPrinted++;
+                iterator++;
+            } else {
+                iterator++;
+                continue; // Won't print
+            }
+            if (amountPrinted == amountToPrint) {
+                break;
+            }
+        }
+    }
+
+}
@@ -0,0 +1,43 @@
+package com.baeldung.customexception;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.util.Scanner;
+
+public class FileManager {
+
+    public static String getFirstLine(String fileName) throws IncorrectFileNameException {
+        try (Scanner file = new Scanner(new File(fileName))) {
+            if (file.hasNextLine()) {
+                return file.nextLine();
+            } else {
+                throw new IllegalArgumentException("Non readable file");
+            }
+        } catch (FileNotFoundException err) {
+            if (!isCorrectFileName(fileName)) {
+                throw new IncorrectFileNameException("Incorrect filename : " + fileName, err);
+            }
+            // Logging etc
+        } catch (IllegalArgumentException err) {
+            if (!containsExtension(fileName)) {
+                throw new IncorrectFileExtensionException("Filename does not contain extension : " + fileName, err);
+            }
+            // Other error cases and logging
+        }
+        return "Default First Line";
+    }
+
+    private static boolean containsExtension(String fileName) {
+        if (fileName.contains(".txt") || fileName.contains(".doc"))
+            return true;
+        return false;
+    }
+
+    private static boolean isCorrectFileName(String fileName) {
+        if (fileName.equals("wrongFileName.txt"))
+            return false;
+        else
+            return true;
+    }
+
+}
@@ -0,0 +1,9 @@
+package com.baeldung.customexception;
+
+public class IncorrectFileExtensionException extends RuntimeException{
+    private static final long serialVersionUID = 1L;
+
+    public IncorrectFileExtensionException(String errorMessage, Throwable err) {
+        super(errorMessage, err);
+    }
+}
@@ -0,0 +1,9 @@
+package com.baeldung.customexception;
+
+public class IncorrectFileNameException extends Exception {
+    private static final long serialVersionUID = 1L;
+    
+    public IncorrectFileNameException(String errorMessage, Throwable err) {
+        super(errorMessage, err);
+    }
+}
@@ -0,0 +1,40 @@
+package com.baeldung.doubles;
+
+import java.math.BigDecimal;
+
+public class SplitFloatingPointNumbers {
+
+    public static void main(String[] args) {
+        
+        double doubleNumber = 24.04;
+        splitUsingFloatingTypes(doubleNumber); 
+        splitUsingString(doubleNumber);
+        splitUsingBigDecimal(doubleNumber);
+    }
+
+    private static void splitUsingFloatingTypes(double doubleNumber) {
+        System.out.println("Using Floating Point Arithmetics:");
+        int intPart = (int) doubleNumber;
+        System.out.println("Double Number: "+doubleNumber);
+        System.out.println("Integer Part: "+ intPart);
+        System.out.println("Decimal Part: "+ (doubleNumber - intPart));
+    }
+
+    private static void splitUsingString(double doubleNumber) {
+        System.out.println("Using String Operations:");
+        String doubleAsString = String.valueOf(doubleNumber);
+        int indexOfDecimal = doubleAsString.indexOf(".");
+        System.out.println("Double Number: "+doubleNumber);
+        System.out.println("Integer Part: "+ doubleAsString.substring(0, indexOfDecimal));
+        System.out.println("Decimal Part: "+ doubleAsString.substring(indexOfDecimal));
+    }
+
+    private static void splitUsingBigDecimal(double doubleNumber) {
+        System.out.println("Using BigDecimal Operations:");
+        BigDecimal bigDecimal = new BigDecimal(String.valueOf(doubleNumber));
+        int intValue = bigDecimal.intValue();
+        System.out.println("Double Number: "+bigDecimal.toPlainString());
+        System.out.println("Integer Part: "+intValue);
+        System.out.println("Decimal Part: "+bigDecimal.subtract(new BigDecimal(intValue)).toPlainString());
+    }
+}
@@ -0,0 +1,19 @@
+package com.baeldung.dynamicproxy;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+
+public class DynamicInvocationHandler implements InvocationHandler {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(DynamicInvocationHandler.class);
+
+    @Override
+    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+        LOGGER.info("Invoked method: {}", method.getName());
+
+        return 42;
+    }
+}
@@ -0,0 +1,36 @@
+package com.baeldung.dynamicproxy;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class TimingDynamicInvocationHandler implements InvocationHandler {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(TimingDynamicInvocationHandler.class);
+    private final Map<String, Method> methods = new HashMap<>();
+
+    private Object target;
+
+    TimingDynamicInvocationHandler(Object target) {
+        this.target = target;
+
+        for(Method method: target.getClass().getDeclaredMethods()) {
+            this.methods.put(method.getName(), method);
+        }
+    }
+
+    @Override
+    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+        long start = System.nanoTime();
+        Object result = methods.get(method.getName()).invoke(target, args);
+        long elapsed = System.nanoTime() - start;
+
+        LOGGER.info("Executing {} finished in {} ns", method.getName(), elapsed);
+
+        return result;
+    }
+}
@@ -0,0 +1,17 @@
+package com.baeldung.enums.values;
+
+/**
+ * This is a simple enum of periodic table elements
+ */
+public enum Element1 {
+    H,
+    HE,
+    LI,
+    BE,
+    B,
+    C,
+    N,
+    O,
+    F,
+    NE
+}
@@ -0,0 +1,52 @@
+package com.baeldung.enums.values;
+
+/**
+ * The simple enum has been enhanced to add the name of the element.
+ */
+public enum Element2 {
+    H("Hydrogen"),
+    HE("Helium"),
+    LI("Lithium"),
+    BE("Beryllium"),
+    B("Boron"),
+    C("Carbon"),
+    N("Nitrogen"),
+    O("Oxygen"),
+    F("Flourine"),
+    NE("Neon");
+
+    /** a final variable to store the label, which can't be changed */
+    public final String label;
+
+    /**
+     * A private constructor that sets the label.
+     * @param label 
+     */
+    private Element2(String label) {
+        this.label = label;
+    }
+
+    /**
+     * Look up Element2 instances by the label field. This implementation iterates through 
+     * the values() list to find the label.
+     * @param label The label to look up
+     * @return The Element2 instance with the label, or null if not found.
+     */
+    public static Element2 valueOfLabel(String label) {
+        for (Element2 e2 : values()) {
+            if (e2.label.equals(label)) {
+                return e2;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Override the toString() method to return the label instead of the declared name.
+     * @return 
+     */
+    @Override
+    public String toString() {
+        return this.label;
+    }
+}
@@ -0,0 +1,63 @@
+package com.baeldung.enums.values;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * A Map has been added to cache labels for faster lookup.
+ */
+public enum Element3 {
+    H("Hydrogen"),
+    HE("Helium"),
+    LI("Lithium"),
+    BE("Beryllium"),
+    B("Boron"),
+    C("Carbon"),
+    N("Nitrogen"),
+    O("Oxygen"),
+    F("Flourine"),
+    NE("Neon");
+
+    /** 
+     * A map to cache labels and their associated Element3 instances.
+     * Note that this only works if the labels are all unique!
+     */
+    private static final Map<String, Element3> BY_LABEL = new HashMap<>();
+    
+    /** populate the BY_LABEL cache */
+    static {
+        for (Element3 e3 : values()) {
+            BY_LABEL.put(e3.label, e3);
+        }
+    }
+
+    /** a final variable to store the label, which can't be changed */
+    public final String label;
+
+    /**
+     * A private constructor that sets the label.
+     * @param label 
+     */
+    private Element3(String label) {
+        this.label = label;
+    }
+
+    /**
+     * Look up Element2 instances by the label field. This implementation finds the
+     * label in the BY_LABEL cache.
+     * @param label The label to look up
+     * @return The Element3 instance with the label, or null if not found.
+     */
+    public static Element3 valueOfLabel(String label) {
+        return BY_LABEL.get(label);
+    }
+
+    /**
+     * Override the toString() method to return the label instead of the declared name.
+     * @return 
+     */
+    @Override
+    public String toString() {
+        return this.label;
+    }
+}
@@ -0,0 +1,95 @@
+package com.baeldung.enums.values;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Multiple fields have been added and the Labeled interface is implemented.
+ */
+public enum Element4 implements Labeled {
+    H("Hydrogen", 1, 1.008f),
+    HE("Helium", 2, 4.0026f),
+    LI("Lithium", 3, 6.94f),
+    BE("Beryllium", 4, 9.01722f),
+    B("Boron", 5, 10.81f),
+    C("Carbon", 6, 12.011f),
+    N("Nitrogen", 7, 14.007f),
+    O("Oxygen", 8, 15.999f),
+    F("Flourine", 9, 18.998f),
+    NE("Neon", 10, 20.180f);
+    /** 
+     * Maps cache labels and their associated Element3 instances.
+     * Note that this only works if the values are all unique!
+     */
+    private static final Map<String, Element4> BY_LABEL = new HashMap<>();
+    private static final Map<Integer, Element4> BY_ATOMIC_NUMBER = new HashMap<>();
+    private static final Map<Float, Element4> BY_ATOMIC_WEIGHT = new HashMap<>();
+    
+    /** populate the caches */
+    static {
+        for (Element4 e4 : values()) {
+            BY_LABEL.put(e4.label, e4);
+            BY_ATOMIC_NUMBER.put(e4.atomicNumber, e4);
+            BY_ATOMIC_WEIGHT.put(e4.atomicWeight, e4);
+        }
+    }
+
+    /** final variables to store the values, which can't be changed */
+    public final String label;
+    public final int atomicNumber;
+    public final float atomicWeight;
+
+    private Element4(String label, int atomicNumber, float atomicWeight) {
+        this.label = label;
+        this.atomicNumber = atomicNumber;
+        this.atomicWeight = atomicWeight;
+    }
+
+    /**
+     * Implement the Labeled interface.
+     * @return the label value
+     */
+    @Override
+    public String label() {
+        return label;
+    }
+
+    /**
+     * Look up Element2 instances by the label field. This implementation finds the
+     * label in the BY_LABEL cache.
+     * @param label The label to look up
+     * @return The Element4 instance with the label, or null if not found.
+     */
+    public static Element4 valueOfLabel(String label) {
+        return BY_LABEL.get(label);
+    }
+
+    /**
+     * Look up Element2 instances by the atomicNumber field. This implementation finds the
+     * atomicNUmber in the cache.
+     * @param number The atomicNumber to look up 
+     * @return The Element4 instance with the label, or null if not found.
+     */
+    public static Element4 valueOfAtomicNumber(int number) {
+        return BY_ATOMIC_NUMBER.get(number);
+    }
+
+    /**
+     * Look up Element2 instances by the atomicWeight field. This implementation finds the
+     * atomic weight in the cache.
+     * @param weight the atomic weight to look up
+     * @return The Element4 instance with the label, or null if not found.
+     */
+    public static Element4 valueOfAtomicWeight(float weight) {
+        return BY_ATOMIC_WEIGHT.get(weight);
+    }
+
+    /**
+     * Override the toString() method to return the label instead of the declared name.
+     * @return 
+     */
+    @Override
+    public String toString() {
+        return this.label;
+    }
+}
--- a/Show More
+++ b/Show More