Merge pull request #13077 from sebx59/master

BAEL-5727 - Determine If a Class Implements an Interface in Java

core-java-modules/core-java-lang-5/pom.xml

@@ -13,6 +13,12 @@
         <artifactId>core-java-modules</artifactId>
         <version>0.0.1-SNAPSHOT</version>
     </parent>
+    
+    <properties>
+        <commons-lang3.version>3.12.0</commons-lang3.version>
+        <reflections.version>0.10.2</reflections.version>
+    </properties>
+    
 
     <build>
         <finalName>core-java-lang-5</finalName>
@@ -24,4 +30,18 @@
         </resources>
     </build>
 
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+    
+        <dependency>
+            <groupId>org.reflections</groupId>
+            <artifactId>reflections</artifactId>
+            <version>${reflections.version}</version>
+        </dependency>
+    </dependencies>
+    
 </project>

core-java-modules/core-java-lang-5/src/main/java/com/baeldung/checkinterface/ChildClass1.java

@@ -0,0 +1,5 @@
+package com.baeldung.checkinterface;
+
+public class ChildClass1 implements ChildInterface1 {
+
+}

core-java-modules/core-java-lang-5/src/main/java/com/baeldung/checkinterface/ChildClass2.java

@@ -0,0 +1,5 @@
+package com.baeldung.checkinterface;
+
+public class ChildClass2 implements ChildInterface2 {
+
+}

core-java-modules/core-java-lang-5/src/main/java/com/baeldung/checkinterface/ChildInterface1.java

@@ -0,0 +1,5 @@
+package com.baeldung.checkinterface;
+
+public interface ChildInterface1 extends MasterInterface {
+
+}

core-java-modules/core-java-lang-5/src/main/java/com/baeldung/checkinterface/ChildInterface2.java

@@ -0,0 +1,5 @@
+package com.baeldung.checkinterface;
+
+public interface ChildInterface2 extends MasterInterface {
+
+}

core-java-modules/core-java-lang-5/src/main/java/com/baeldung/checkinterface/MasterClass.java

@@ -0,0 +1,5 @@
+package com.baeldung.checkinterface;
+
+public class MasterClass implements MasterInterface {
+
+}

core-java-modules/core-java-lang-5/src/main/java/com/baeldung/checkinterface/MasterInterface.java

@@ -0,0 +1,5 @@
+package com.baeldung.checkinterface;
+
+public interface MasterInterface {
+
+}

core-java-modules/core-java-lang-5/src/test/java/com/baeldung/checkinterface/CheckInterfaceUnitTest.java

@@ -0,0 +1,154 @@
+package com.baeldung.checkinterface;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import org.apache.commons.lang3.ClassUtils;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.reflections.ReflectionUtils;
+import org.reflections.Reflections;
+
+public class CheckInterfaceUnitTest {
+    
+    protected static Reflections reflections;
+    
+    @BeforeAll
+    public static void initializeReflectionsLibrary() {
+        
+        reflections = new Reflections("com.baeldung.checkinterface");
+    }
+
+    @Test
+    public void whenUsingReflectionGetInterfaces_thenDirectlyImplementedInterfaceIsFound() {
+        
+        ChildClass2 childClass2 = new ChildClass2();        
+        List<Class<?>> interfaces = Arrays.asList(childClass2.getClass().getInterfaces());
+        
+        assertEquals(1, interfaces.size());
+        assertTrue(interfaces.contains(ChildInterface2.class));
+    }
+    
+    @Test
+    public void whenUsingReflectionGetInterfaces_thenParentInterfaceIsNotFound() {
+        
+        ChildClass2 childClass2 = new ChildClass2();        
+        List<Class<?>> interfaces = Arrays.asList(childClass2.getClass().getInterfaces());
+        
+        assertFalse(interfaces.contains(MasterInterface.class));
+    }
+    
+    @Test
+    public void whenUsingReflectionGetInterfacesRecursively_thenParentInterfaceIsFound() {
+        
+        Set<Class<?>> interfaces = getAllExtendedOrImplementedInterfacesRecursively(ChildClass2.class);
+        
+        assertTrue(interfaces.contains(ChildInterface2.class));
+        assertTrue(interfaces.contains(MasterInterface.class));
+    }
+    
+    @Test
+    public void whenUsingReflectionIsAssignableFrom_thenDirectlyImplementedInterfaceIsFound() {
+        
+        ChildClass2 childClass2 = new ChildClass2();        
+        
+        assertTrue(ChildInterface2.class.isAssignableFrom(childClass2.getClass()));
+    }
+    
+    @Test
+    public void whenUsingReflectionIsAssignableFrom_thenParentInterfaceIsFound() {
+        
+        ChildClass2 childClass2 = new ChildClass2();        
+        
+        assertTrue(MasterInterface.class.isAssignableFrom(childClass2.getClass()));
+    }
+    
+    @Test
+    public void whenUsingReflectionIsInstance_thenDirectlyImplementedInterfaceIsFound() {
+        
+        ChildClass2 childClass2 = new ChildClass2();        
+        
+        assertTrue(ChildInterface2.class.isInstance(childClass2));
+    }
+    
+    @Test
+    public void whenUsingReflectionIsInstance_thenParentInterfaceIsFound() {
+        
+        ChildClass2 childClass2 = new ChildClass2();        
+        
+        assertTrue(MasterInterface.class.isInstance(childClass2));
+    }
+    
+    @Test
+    public void whenUsingReflectionInstanceOf_thenDirectlyImplementedInterfaceIsFound() {
+        
+        ChildClass2 childClass2 = new ChildClass2();        
+        
+        assertTrue(childClass2 instanceof ChildInterface2);
+    }
+    
+    @Test
+    public void whenUsingReflectionInstanceOf_thenParentInterfaceIsFound() {
+        
+        ChildClass2 childClass2 = new ChildClass2();        
+        
+        assertTrue(childClass2 instanceof MasterInterface);
+    }
+    
+    @Test
+    public void whenUsingCommons_thenDirectlyImplementedInterfaceIsFound() {
+        
+        ChildClass2 childClass2 = new ChildClass2();        
+        List<Class<?>> interfaces = ClassUtils.getAllInterfaces(childClass2.getClass());
+        
+        assertTrue(interfaces.contains(ChildInterface2.class));
+    }
+    
+    @Test
+    public void whenUsingCommons_thenParentInterfaceIsFound() {
+        
+        ChildClass2 childClass2 = new ChildClass2();        
+        List<Class<?>> interfaces = ClassUtils.getAllInterfaces(childClass2.getClass());
+        
+        assertTrue(interfaces.contains(MasterInterface.class));
+    }
+    
+    @Test
+    public void whenUsingReflections_thenDirectlyImplementedInterfaceIsFound() {
+        
+        ChildClass2 childClass2 = new ChildClass2();        
+        Set<Class<?>> interfaces = reflections.get(ReflectionUtils.Interfaces.of(childClass2.getClass()));
+        
+        assertTrue(interfaces.contains(ChildInterface2.class));
+    }
+    
+    @Test
+    public void whenUsingReflections_thenParentInterfaceIsFound() {
+        
+        ChildClass2 childClass2 = new ChildClass2();        
+        Set<Class<?>> interfaces = reflections.get(ReflectionUtils.Interfaces.of(childClass2.getClass()));
+        
+        assertTrue(interfaces.contains(MasterInterface.class));
+    }
+    
+    static Set<Class<?>> getAllExtendedOrImplementedInterfacesRecursively(Class<?> clazz) { 
+        
+        Set<Class<?>> res = new HashSet<Class<?>>(); 
+        Class<?>[] interfaces = clazz.getInterfaces(); 
+        
+        if (interfaces.length > 0) { 
+            res.addAll(Arrays.asList(interfaces)); 
+            for (Class<?> interfaze : interfaces) { 
+                res.addAll(getAllExtendedOrImplementedInterfacesRecursively(interfaze)); 
+                } 
+            } 
+        
+        return res; 
+       }
+}