Merge pull request #16665 from sk1418/map-not-null-elements

[map-not-null-elements] map+filter

Author: theangrydev

core-java-modules/core-java-streams-6/src/test/java/com/baeldung/streams/mapnotnull/ReturnNotNullElementsFromStreamMapUnitTest.java

@@ -0,0 +1,61 @@
+package com.baeldung.streams.mapnotnull;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+import org.junit.jupiter.api.Test;
+
+public class ReturnNotNullElementsFromStreamMapUnitTest {
+
+    private static final List<String> INPUT = List.of("f o o", "a,b,c,d", "b a r", "w,x,y,z", "w,o,w");
+    private static final List<String> EXPECTED = List.of("a b c d", "w x y z", "w o w");
+
+    private String commaToSpace(String input) {
+        if (input.contains(",")) {
+            return input.replaceAll(",", " ");
+        } else {
+            return null;
+        }
+    }
+
+    @Test
+    void whenUseMapAndFilter_thenGetTheExpectedResult() {
+        List<String> result = INPUT.stream()
+            .map(str -> commaToSpace(str))
+            .filter(Objects::nonNull)
+            .collect(Collectors.toList());
+        assertEquals(EXPECTED, result);
+    }
+
+    @Test
+    void whenUseOptional_thenGetTheExpectedResult() {
+        //unnecessarily wrapping in Optional, not recommended
+        List<String> result = INPUT.stream()
+            .map(str -> Optional.ofNullable(commaToSpace(str)))
+            .filter(Optional::isPresent)
+            .map(Optional::get)
+            .collect(Collectors.toList());
+        assertEquals(EXPECTED, result);
+    }
+
+    private Optional<String> commaToSpaceOptional(String input) {
+        if (input.contains(",")) {
+            return Optional.of(input.replaceAll(",", " "));
+        } else {
+            return Optional.empty();
+        }
+    }
+
+    @Test
+    void whenUseMapAndFilterWithOptionalReturnValues_thenGetTheExpectedResult() {
+        List<String> result = INPUT.stream()
+            .map(str -> commaToSpaceOptional(str).orElse(null))
+            .filter(Objects::nonNull)
+            .collect(Collectors.toList());
+        assertEquals(EXPECTED, result);
+    }
+}