Bael-6331: Adding changes for creating and checking empty streams (#14047)

* BAEL-6331: Create EmptyStreams.java

* BAEL-6331: Create EmptyStreamsUnitTest.java

core-java-modules/core-java-streams-5/src/main/java/com/baeldung/streams/emptystreams/EmptyStreams.java

@@ -0,0 +1,49 @@
+package com.baeldung.streams.emptystreams;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Optional;
+import java.util.function.Supplier;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+public class EmptyStreams {
+
+    public static void main(String[] args) {
+
+        createEmptyStreams();
+        checkForEmptyStreamUsingSupplier();
+    }
+
+    private static void createEmptyStreams() {
+        
+        // Using Stream.empty()
+        Stream<String> emptyStream = Stream.empty();
+        System.out.println(emptyStream.findAny().isEmpty());
+        
+        // Using Stream.of()
+        emptyStream = Stream.of();
+        System.out.println(emptyStream.findAny().isEmpty());
+
+        // Empty Stream of primitive type
+        IntStream emptyIntStream = IntStream.of(new int[] {});
+        System.out.println(emptyIntStream.findAny().isEmpty());
+        
+        // Using Arrays.stream()
+        emptyIntStream = Arrays.stream(new int[] {});
+        System.out.println(emptyIntStream.findAny().isEmpty());
+
+        // Using list.stream()
+        Stream<Integer> collectionStream = new ArrayList<Integer>().stream();
+        System.out.println(collectionStream.findAny().isEmpty());
+    }
+     
+    private static void checkForEmptyStreamUsingSupplier() {
+        Supplier<Stream<Integer>> streamSupplier = () -> Stream.of(1, 2, 3, 4, 5).filter(number -> number > 5);
+
+        Optional<Integer> result1 = streamSupplier.get().findAny();
+        System.out.println(result1.isEmpty());
+        Optional<Integer> result2 = streamSupplier.get().findFirst();
+        System.out.println(result2.isEmpty());
+    }
+}

core-java-modules/core-java-streams-5/src/test/java/com/baeldung/streams/emptystreams/EmptyStreamsUnitTest.java

@@ -0,0 +1,44 @@
+package com.baeldung.streams.emptystreams;
+
+import static org.junit.Assert.assertTrue;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Optional;
+import java.util.function.Supplier;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+import org.junit.Test;
+
+public class EmptyStreamsUnitTest {
+
+    @Test
+    public void givenEmptyStreams_findAnyReturnsAnEmptyOptional() {
+
+        Stream<String> emptyStream = Stream.empty();
+        assertTrue(emptyStream.findAny().isEmpty());
+
+        emptyStream = Stream.of();
+        assertTrue(emptyStream.findAny().isEmpty());
+
+        IntStream emptyIntStream = IntStream.of(new int[] {});
+        assertTrue(emptyIntStream.findAny().isEmpty());
+
+        emptyIntStream = Arrays.stream(new int[] {});
+        assertTrue(emptyIntStream.findAny().isEmpty());
+
+        Stream<Integer> collectionStream = new ArrayList<Integer>().stream();
+        assertTrue(collectionStream.findAny().isEmpty());
+    }
+
+    @Test
+    public void givenAStreamToSupplier_NewInstanceOfTheStreamIsReturnedForEveryGetCall() {
+        Supplier<Stream<Integer>> streamSupplier = () -> Stream.of(1, 2, 3, 4, 5).filter(number -> number > 5);
+
+        Optional<Integer> result1 = streamSupplier.get().findAny();
+        assertTrue(result1.isEmpty());
+        Optional<Integer> result2 = streamSupplier.get().findFirst();
+        assertTrue(result2.isEmpty());
+    }
+}