How to use Java Reflection

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For the reflection examples, lets consider this Dog class

   package ref;

/**
 *
 * @author Rukshan
 */
public class Dog {
    
    private String name;
    public String type;
   
    public Dog() {        
    }

    private Dog(String type) {
        this.type=type;
    }  
    
    public void setName(String name) {
        this.name=name;
    }
    
    public void setType(String type){
        this.type=type;
    }
    
    public String getName(){
        return this.name;
    }

    public String getType(){
        return this.type;
    }
    
    private String Bark(String sound){
        return "Barked "+sound;
    }
}

Get the value of a field of object

   public static void getField() {
        try {
            Dog dog = new Dog();
            dog.setType("dog");
            Class<?> dogClass = dog.getClass();
            Field type = dogClass.getDeclaredField("type");
            String value = (String) type.get(dog);
            System.out.println(value);

        } catch (NoSuchFieldException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (SecurityException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalArgumentException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Get the value of protected field of object

	public static void getProtectedField() {
        try {
            Dog dog = new Dog();
            dog.setName("lucky");
            Class<?> dogClass = dog.getClass();
            Field name = dogClass.getDeclaredField("name");
            name.setAccessible(true);
            String value = (String) name.get(dog);
            System.out.println(value);

        } catch (NoSuchFieldException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (SecurityException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalArgumentException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Set the value of field in Object

      public static void setField() {
        try {
            Dog dog = new Dog();
            Class<?> dogClass = dog.getClass();
            Field type = dogClass.getDeclaredField("type");
            String value = "Dog";
            type.set(dog, value);
            System.out.println(dog.getType());

        } catch (NoSuchFieldException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (SecurityException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalArgumentException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Set the value of protected field in object

       public static void setProtectedField() {
        try {
            Dog dog = new Dog();
            Class<?> dogClass = dog.getClass();
            Field name = dogClass.getDeclaredField("name");
            String value = "Lucky";
            name.setAccessible(true);
            name.set(dog, value);
            System.out.println(dog.getName());

        } catch (NoSuchFieldException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (SecurityException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalArgumentException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Invoke method

      public static void invokeMethod() {
        try {
            Dog dog = new Dog();
            Class<?> dogClass = dog.getClass();
            Method setName = dogClass.getDeclaredMethod("setName", new Class[]{String.class});
            setName.invoke(dog, new Object[]{"Lucky"});
            System.out.println(dog.getName());
        } catch (SecurityException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalArgumentException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (NoSuchMethodException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (InvocationTargetException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Invoke proteced methods and get return value

      public static void invokeProtectedMethod() {
        try {
            Dog dog = new Dog();
            Class<?> dogClass = dog.getClass();
            Method bark = dogClass.getDeclaredMethod("Bark", new Class[]{String.class});
            bark.setAccessible(true);
            Object ob = bark.invoke(dog, new Object[]{"awwww"});
            String value = (String) ob;
            System.out.println(value);
        } catch (SecurityException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalArgumentException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (NoSuchMethodException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (InvocationTargetException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Create Instance with constructor

      public static void constructor(){
        try {
            Class<?> dogClass=Class.forName("ref.Dog");
            Constructor<?> construct=dogClass.getConstructor();
            Object dog=construct.newInstance();
            
            Method bark = dogClass.getDeclaredMethod("Bark", new Class[]{String.class});
            bark.setAccessible(true);
            Object ob = bark.invoke(dog, new Object[]{"huuuuu"});
            String value = (String) ob;
            System.out.println(value);
            
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (NoSuchMethodException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (SecurityException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalArgumentException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (InvocationTargetException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Create Instance with proteced constructor

      public static void protectedConstructor(){
        try {
            Class<?> dogClass=Class.forName("ref.Dog");
            Constructor<?> construct=dogClass.getConstructor();
            construct.setAccessible(true);
            Object dog=construct.newInstance();
            
            Method bark = dogClass.getDeclaredMethod("Bark", new Class[]{String.class});
            bark.setAccessible(true);
            Object ob = bark.invoke(dog, new Object[]{"awwww huuuuu"});
            String value = (String) ob;
            System.out.println(value);
            
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (NoSuchMethodException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (SecurityException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalArgumentException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        } catch (InvocationTargetException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Get the declared filed of a class

      public static void getFields(){
        try {
            Class<?> dogClass=Class.forName("ref.Dog");
            Field[] fields=dogClass.getDeclaredFields();
            for (Field field : fields) {
                System.out.println(field.getName()+" "+field.getType().getCanonicalName());
            }
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Get Declared methods and method parameters of a class

      public static void getMethods(){
        try {
            Class<?> dogClass=Class.forName("ref.Dog");
            Method[] methods=dogClass.getDeclaredMethods();
            for (Method method : methods) {
                System.out.println(method.getName()+" "+method.getReturnType().getCanonicalName());
                for (Class<?> class1 : method.getParameterTypes()) {
                    System.out.println(class1.getCanonicalName());
                }
                
            }
            
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(Ref.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Download the Source code from here

2014-09-19 07:33:04 | Rukshan Chathuranga

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