reflection api using and isInstance vs instanceof

Author: serdaralkancode

src/main/java/tr/salkan/code/java/pure/examples/reflection/IsInstanceVsInstanceof.java

@@ -0,0 +1,55 @@
+package tr.salkan.code.java.pure.examples.reflection;
+
+public class IsInstanceVsInstanceof {
+
+ /*
+ isInstance -> class is decided at run time. (late binding) e.g.
+ instanceof -> you need to know the exact class at compile time.
+ */
+
+ public static void main(String[] args) {
+
+ TestExampleCls obj1 = new TestExampleCls(1,"A");
+
+ Integer i = 4;
+ String s = "Hello";
+
+ if(obj1 instanceof TestExampleCls)
+ {
+ System.out.println("Yes TestExampleCls");
+ }
+
+ // it is error in compile time -> IDE warn -> Cannot cast Integer
+// if(obj1 instanceof Integer)
+// {
+//
+// }
+
+
+ // it is error in compile time -> IDE warn -> Cannot cast TestExampleCls
+// if(i instanceof TestExampleCls)
+// {
+//
+// }
+
+ try
+ {
+ boolean intComp = isInstanceTest(i,"java.lang.Integer");
+ boolean strComp = isInstanceTest(s,"java.lang.String");
+
+ System.out.println(" intComp : " + intComp + " strComp :" + strComp);
+ }
+ catch (ClassNotFoundException e)
+ {
+ e.printStackTrace();
+ }
+
+
+ }
+
+ private static boolean isInstanceTest(Object obj, String str) throws ClassNotFoundException {
+
+ return Class.forName(str).isInstance(obj);
+ }
+
+}

src/main/java/tr/salkan/code/java/pure/examples/reflection/ReflectionExample1.java

@@ -0,0 +1,131 @@
+package tr.salkan.code.java.pure.examples.reflection;
+
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Field;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+class TestClass
+{
+
+ private String stringValue;
+
+ public TestClass() { stringValue = "TestClass"; }
+
+
+ public void testMethod1() {
+ System.out.println("TestClass, public testMethod1 method call and private string value : " + stringValue);
+ }
+
+
+ public void testMethod2(int n) {
+ System.out.println("TestClass, public testMethod2 method call with arg : " + n);
+ }
+
+ private void testMethod3() {
+ System.out.println("TestClass, private testMethod3 call");
+ }
+}
+
+public class ReflectionExample1 {
+
+
+ public static void main(String[] args) {
+
+ TestClass testClass = new TestClass();
+
+ Class cls = testClass.getClass();
+
+ System.out.println("class name : " + cls.getName());
+
+ System.out.println("--------------------------");
+ try
+ {
+ Constructor constructor = cls.getConstructor();
+
+ System.out.println(" class constructor name : " + constructor.getName());
+ }
+ catch (NoSuchMethodException e)
+ {
+ System.out.println("getConstructor exception : " + e.getMessage());
+ }
+
+ System.out.println("--------------------------");
+
+ //methods of class
+ Method[] methods = cls.getMethods();
+
+ for (Method method:methods)
+ {
+ System.out.println("class method : " + method.getName());
+ }
+
+ System.out.println("--------------------------");
+
+ try
+ {
+ // NoSuchMethodException
+ Method testMethod1Call = cls.getDeclaredMethod("testMethod1");
+
+ //IllegalAccessException and InvocationTargetException
+ testMethod1Call.invoke(testClass);
+ }
+ catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e)
+ {
+ System.out.println(" error : " + e.getMessage());
+ }
+
+ System.out.println("--------------------------");
+
+ try
+ {
+ // NoSuchMethodException
+ Method testMethod2Call = cls.getDeclaredMethod("testMethod2", int.class);
+
+ //IllegalAccessException and InvocationTargetException
+ testMethod2Call.invoke(testClass, 10);
+ }
+ catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e)
+ {
+
+ System.out.println(" error : " + e.getMessage());
+ }
+
+ System.out.println("--------------------------");
+
+ try
+ {
+ //get property -> NoSuchFieldException
+ Field field = cls.getDeclaredField("stringValue");
+
+ field.setAccessible(true);
+
+ //new value set property -> IllegalAccessException
+ field.set(testClass, "TestClass field set new value");
+ }
+ catch (NoSuchFieldException | IllegalAccessException e)
+ {
+ System.out.println("error : " + e.getMessage());
+ }
+
+ System.out.println("--------------------------");
+
+ try
+ {
+ Method testMethod3Call = cls.getDeclaredMethod("testMethod3");
+
+ testMethod3Call.setAccessible(true);
+
+ testMethod3Call.invoke(testClass);
+ }
+ catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e)
+ {
+ System.out.println("error : " + e.getMessage());
+ }
+
+
+ }
+
+
+}

src/main/java/tr/salkan/code/java/pure/examples/reflection/ReflectionExample2.java

@@ -0,0 +1,40 @@
+package tr.salkan.code.java.pure.examples.reflection;
+
+import java.lang.reflect.Constructor;
+import java.util.Arrays;
+
+public class ReflectionExample2 {
+
+ class Test1 {
+
+ private String str = "Test1 str";
+
+ public Test1() {
+
+ }
+ }
+
+ private static class Test2 {
+
+ private class Test2InnerClass {
+
+ private int i;
+
+ private Test2InnerClass(int i) {
+ this.i = i;
+ }
+ }
+ }
+
+ public static void main(String[] args) throws NoSuchMethodException {
+
+ Class<Test2.Test2InnerClass> c = Test2.Test2InnerClass.class;
+
+ Constructor<Test2.Test2InnerClass> constructor = c.getDeclaredConstructor(Test2.class, int.class);
+
+ System.out.println(constructor);
+ System.out.println(constructor.getName());
+ System.out.println(Arrays.toString(constructor.getParameters()));
+
+ }
+}

src/main/java/tr/salkan/code/java/pure/examples/reflection/ReflectionExample3.java

@@ -0,0 +1,50 @@
+package tr.salkan.code.java.pure.examples.reflection;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+
+public class ReflectionExample3 {
+
+ /*
+ getConstructor() -> public Constructor
+ getDeclaredConstructor -> any acess Constructor (public,private,protected )
+ */
+
+ public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException, ClassNotFoundException {
+
+
+ Class testclz = Class.forName("tr.salkan.code.java.pure.examples.reflection.TestReflectionClass");
+
+ System.out.println(testclz);
+ Constructor<?> constructor = testclz.getConstructor();
+
+ System.out.println(constructor);
+
+ Class[] parameterType = new Class[1];
+ parameterType[0] = int.class;
+
+ System.out.println(TestReflectionClass.class.getDeclaredConstructor(parameterType));
+
+ Constructor<TestReflectionClass> constructorParam = testclz.getDeclaredConstructor(new Class[] {int.class});
+
+ System.out.println(constructorParam);
+
+ Constructor[] constructors = testclz.getDeclaredConstructors();
+
+ System.out.println("----------------------------------------");
+
+ for (Constructor c : constructors) {
+
+ String name = c.getName();
+ System.out.println("Constructor name= " + name);
+
+ Class[] paramterTypes = c.getParameterTypes();
+ for (Class p : paramterTypes) {
+ System.out.println("Param type name = " + p.getName());
+ }
+ System.out.println("----------------------------------------");
+ }
+
+
+ }
+}

src/main/java/tr/salkan/code/java/pure/examples/reflection/TestExampleCls.java

@@ -0,0 +1,28 @@
+package tr.salkan.code.java.pure.examples.reflection;
+
+public class TestExampleCls {
+
+ private int v1;
+ private String v2;
+
+ public TestExampleCls(int v1, String v2) {
+ this.v1 = v1;
+ this.v2 = v2;
+ }
+
+ public int getV1() {
+ return v1;
+ }
+
+ public void setV1(int v1) {
+ this.v1 = v1;
+ }
+
+ public String getV2() {
+ return v2;
+ }
+
+ public void setV2(String v2) {
+ this.v2 = v2;
+ }
+}

src/main/java/tr/salkan/code/java/pure/examples/reflection/TestReflectionClass.java

@@ -0,0 +1,21 @@
+package tr.salkan.code.java.pure.examples.reflection;
+
+public class TestReflectionClass {
+
+ public TestReflectionClass() {
+
+ System.out.println("TestReflectionClass default constructor");
+ }
+
+ public TestReflectionClass(int a){
+ System.out.println("TestReflectionClass Constructor int : "+a);
+ }
+
+ private TestReflectionClass(String s){
+ System.out.println("TestReflectionClass Constructor string : "+s);
+ }
+
+ protected TestReflectionClass(Long l){
+ System.out.println("TestReflectionClass Constructor Long : "+l);
+ }
+}