Bael 7163 (#15532)

* Create StreamFromEmptyList.java Initial Commit * Create StreamFromEmptyListUnitTest.java Initial commit of StreamFromEmptyListUnitTest. * Create README.md Adding README file. * Create pom.xml * Create pom.xml * Create REAME.md * Delete core-java-modules/core-java-streams-6/src/README.md * Delete core-java-modules/core-java-streams-6/src/pom.xml * Update pom.xml * Update pom.xml
2024-01-09 10:11:00 +05:30
parent c23c21e38e
commit 40dc851047
5 changed files with 172 additions and 0 deletions
@@ -0,0 +1,56 @@
+package com.baeldung.streams.emptylists;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class StreamFromEmptyList {
+
+    public static void main(String[] args) {
+        createStreamFromEmptyList();
+       
+        List<String> nameList = getList();
+        printNameLengths(nameList); // passing null
+        printNameLengths((nameList == null) ? List.of() : nameList); // passing empty list
+        
+        collectStreamOfEmptyListToAnotherList();
+    }
+
+    private static void collectStreamOfEmptyListToAnotherList() {
+        List<String> emptyList = new ArrayList<>();
+        List<String> collectedList = emptyList.stream().collect(Collectors.toList());
+
+        System.out.println(collectedList.size() == 0);
+
+        collectedList = emptyList.stream().filter(s -> s.startsWith("a")).collect(Collectors.toList());
+        System.out.println(collectedList.size() == 0);
+    }
+
+    private static void createStreamFromEmptyList() {
+        List<String> emptyList = new ArrayList<>();
+        Stream<String> emptyStream = emptyList.stream();
+        System.out.println(emptyStream.findAny().isEmpty());
+    }
+
+    private static void printNameLengths(List<String> nameList) {
+        // Without Stream - Traditional approach with null check
+        if (nameList != null) {
+            for (String name : nameList) {
+                System.out.println("Length of " + name + ": " + name.length());
+            }
+        } else {
+            System.out.println("List is null. Unable to process.");
+        }
+
+        // With Stream - More concise approach
+        Optional.ofNullable(nameList).ifPresent(list -> list.stream()
+                .map(name -> "Length of " + name + ": " + name.length()).forEach(System.out::println));
+    }
+
+    private static List<String> getList() {
+        // This method may return null for demonstration purposes
+        return null;
+    }
+}
@@ -0,0 +1,27 @@
+package com.baeldung.streams.emptylists;
+
+import static org.junit.Assert.assertTrue;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import org.junit.Test;
+
+public class StreamFromEmptyListUnitTest {
+
+    @Test
+    public void givenEmptyList_whenConvertedToStream_thenResultantStreamIsEmpty() {
+        List<String> emptyList = new ArrayList<>();
+        Stream<String> emptyStream = emptyList.stream();
+        assertTrue(emptyStream.findAny().isEmpty());
+    }
+
+    @Test
+    public void givenEmptyList_whenCollectStreamOfEmptyListToAnotherList_thenResultantListIsEmpty() {
+        List<String> emptyList = new ArrayList<>();
+        List<String> collectedList = emptyList.stream().collect(Collectors.toList());
+        assertTrue(collectedList.isEmpty());
+    }
+}