Collection to Stream without nulls in core-java-collections (#4903)

core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingCommonsEmptyIfNullUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.nullsafecollectionstreams;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.stream.Stream;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class NullSafeCollectionStreamsUsingCommonsEmptyIfNullUnitTest {
+
+    private final NullSafeCollectionStreamsUsingCommonsEmptyIfNull instance =
+            new NullSafeCollectionStreamsUsingCommonsEmptyIfNull();
+    @Test
+    public void whenCollectionIsNull_thenExpectAnEmptyStream() {
+        Collection<String> collection = null;
+        Stream<String> expResult = Stream.empty();
+        Stream<String> result = instance.collectionAsStream(collection);
+        assertStreamEquals(expResult, result);
+    }
+
+    @Test
+    public void whenCollectionHasElements_thenExpectAStreamOfExactlyTheSameElements() {
+        Collection<String> collection = Arrays.asList("a", "b", "c");
+        Stream<String> expResult = Arrays.stream(new String[] { "a", "b", "c" });
+        Stream<String> result = instance.collectionAsStream(collection);
+        assertStreamEquals(expResult, result);
+    }
+
+    private static void assertStreamEquals(Stream<?> s1, Stream<?> s2) {
+        Iterator<?> iter1 = s1.iterator(), iter2 = s2.iterator();
+        while (iter1.hasNext() && iter2.hasNext())
+            assertEquals(iter1.next(), iter2.next());
+        assert !iter1.hasNext() && !iter2.hasNext();
+    }
+
+}

core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingJava8OptionalContainerUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.nullsafecollectionstreams;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.stream.Stream;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class NullSafeCollectionStreamsUsingJava8OptionalContainerUnitTest {
+
+    private final NullSafeCollectionStreamsUsingJava8OptionalContainer instance =
+            new NullSafeCollectionStreamsUsingJava8OptionalContainer();
+    @Test
+    public void whenCollectionIsNull_thenExpectAnEmptyStream() {
+        Collection<String> collection = null;
+        Stream<String> expResult = Stream.empty();
+        Stream<String> result = instance.collectionAsStream(collection);
+        assertStreamEquals(expResult, result);
+    }
+
+    @Test
+    public void whenCollectionHasElements_thenExpectAStreamOfExactlyTheSameElements() {
+        Collection<String> collection = Arrays.asList("a", "b", "c");
+        Stream<String> expResult = Arrays.stream(new String[] { "a", "b", "c" });
+        Stream<String> result = instance.collectionAsStream(collection);
+        assertStreamEquals(expResult, result);
+    }
+
+    private static void assertStreamEquals(Stream<?> s1, Stream<?> s2) {
+        Iterator<?> iter1 = s1.iterator(), iter2 = s2.iterator();
+        while (iter1.hasNext() && iter2.hasNext())
+            assertEquals(iter1.next(), iter2.next());
+        assert !iter1.hasNext() && !iter2.hasNext();
+    }
+
+}

core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingNullDereferenceCheckUnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.nullsafecollectionstreams;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.stream.Stream;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class NullSafeCollectionStreamsUsingNullDereferenceCheckUnitTest {
+
+    private final NullSafeCollectionStreamsUsingNullDereferenceCheck instance =
+            new NullSafeCollectionStreamsUsingNullDereferenceCheck();
+
+    @Test
+    public void whenCollectionIsNull_thenExpectAnEmptyStream() {
+        Collection<String> collection = null;
+        Stream<String> expResult = Stream.empty();
+        Stream<String> result = instance.collectionAsStream(collection);
+        assertStreamEquals(expResult, result);
+    }
+
+    @Test
+    public void whenCollectionHasElements_thenExpectAStreamOfExactlyTheSameElements() {
+        Collection<String> collection = Arrays.asList("a", "b", "c");
+        Stream<String> expResult = Arrays.stream(new String[] { "a", "b", "c" });
+        Stream<String> result = instance.collectionAsStream(collection);
+        assertStreamEquals(expResult, result);
+    }
+
+    private static void assertStreamEquals(Stream<?> s1, Stream<?> s2) {
+        Iterator<?> iter1 = s1.iterator(), iter2 = s2.iterator();
+        while (iter1.hasNext() && iter2.hasNext())
+            assertEquals(iter1.next(), iter2.next());
+        assert !iter1.hasNext() && !iter2.hasNext();
+    }
+
+}