BAEL-4936: Completed artcile Abstract class with default method vs interface

core-java-modules/core-java-8-2/src/main/java/com/baeldung/interfaceVsAbstractClass/ChidlCircleInterfaceImpl.java

@@ -0,0 +1,13 @@
+package com.baeldung.interfaceVsAbstractClass;
+
+public class ChidlCircleInterfaceImpl implements CircleInterface {
+    private String color;
+
+    public String getColor() {
+        return color;
+    }
+
+    public void setColor(String color) {
+        this.color = color;
+    }
+}

core-java-modules/core-java-8-2/src/main/java/com/baeldung/interfaceVsAbstractClass/ChildCircleClass.java

@@ -0,0 +1,5 @@
+package com.baeldung.interfaceVsAbstractClass;
+
+public class ChildCircleClass extends CircleClass {
+
+}

core-java-modules/core-java-8-2/src/main/java/com/baeldung/interfaceVsAbstractClass/CircleClass.java

@@ -0,0 +1,27 @@
+package com.baeldung.interfaceVsAbstractClass;
+
+import java.util.Arrays;
+import java.util.List;
+
+public abstract class CircleClass {
+
+    private String color;
+    private List<String> allowedColors = Arrays.asList("RED", "GREEN", "BLUE");
+
+    public boolean isValid() {
+        if (allowedColors.contains(getColor())) {
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    public String getColor() {
+        return color;
+    }
+
+    public void setColor(String color) {
+        this.color = color;
+    }
+
+}

core-java-modules/core-java-8-2/src/main/java/com/baeldung/interfaceVsAbstractClass/CircleInterface.java

@@ -0,0 +1,16 @@
+package com.baeldung.interfaceVsAbstractClass;
+
+import java.util.Arrays;
+import java.util.List;
+
+public interface CircleInterface {
+    List<String> allowedColors = Arrays.asList("RED", "GREEN", "BLUE");
+
+    public default boolean isValid(String color) {
+        if (allowedColors.contains(color)) {
+            return true;
+        } else {
+            return false;
+        }
+    }
+}

core-java-modules/core-java-8-2/src/test/java/com/baeldung/interfaceVsAbstractClass/InterfaceVsAbstractClassUnitTest.java

@@ -0,0 +1,36 @@
+package com.baeldung.interfaceVsAbstractClass;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class InterfaceVsAbstractClassUnitTest {
+    @Test
+    public void givenAbstractClass_whenValidCircleUsedThenPass() {
+        CircleClass redCircle = new ChildCircleClass();
+        redCircle.setColor("RED");
+        assertTrue(redCircle.isValid());
+    }
+
+    @Test
+    public void givenAbstractClass_whenInvalidCircleUsedThenFail() {
+        CircleClass redCircle = new ChildCircleClass();
+        redCircle.setColor("WHITE");
+        assertFalse(redCircle.isValid());
+    }
+
+    @Test
+    public void givenInterface_whenValidCircleWithoutStateUsedThenPass() {
+        ChidlCircleInterfaceImpl redCircleWithoutState = new ChidlCircleInterfaceImpl();
+        redCircleWithoutState.setColor("RED");
+        assertTrue(redCircleWithoutState.isValid(redCircleWithoutState.getColor()));
+    }
+
+    @Test
+    public void givenInterface_whenInvalidCircleWithoutStateUsedThenFail() {
+        ChidlCircleInterfaceImpl redCircleWithoutState = new ChidlCircleInterfaceImpl();
+        redCircleWithoutState.setColor("WHITE");
+        assertFalse(redCircleWithoutState.isValid(redCircleWithoutState.getColor()));
+    }
+}