Proxy Pattern

Main.java

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class Main
{
	public static void main(String[] args) {
		Original original = new Original();
        Handler handler = new Handler(original);
        If f = (If) Proxy.newProxyInstance(If.class.getClassLoader(),
                new Class[] { If.class },
                handler);
        f.oriMethod("Hallo");
	}
	
	interface If {
	    void oriMethod(String s);
	}
	
	static class Original implements If {
	    public void oriMethod(String s) {
	        System.out.println(s);
	    }
	}
	
	static class Handler implements InvocationHandler {
	    private final If ori;
	    
	    public Handler(If ori) {
	        this.ori = ori;
	    }
	    
	    public Object invoke(Object proxy, Method method, Object[] args) 
	        throws IllegalAccessException, 
	                IllegalArgumentException, 
	                InvocationTargetException {
	        System.out.println("BEFORE");
            method.invoke(ori, args);
            System.out.println("AFTER");
            return null;
	    }
	}
}