动态代理

第一步：实现钢笔接口

interface PenInterface {

    void write();

    void draw();

}

第二步：学生的手实现钢笔接口

public class StudentHand implements PenInterface {

    @Override
    public void write() {
        System.out.println("学生用笔写字");

    }

    @Override
    public void draw() {
        System.out.println("学生用笔画画");
    }

}

第三步：学生代理的功能

public class StudentProxy implements InvocationHandler {

    private Object mTarget;

    public StudentProxy(Object target) {
        mTarget = target;
    }

    public Object getInstance() {
        return Proxy.newProxyInstance(mTarget.getClass().getClassLoader(), mTarget.getClass().getInterfaces(), this);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        doSthBefore();
        Object object = method.invoke(mTarget, args);
        doSthAfter();
        return object;
    }

    private void doSthBefore() {
        System.out.println("调用方法之前");
    }

    private void doSthAfter() {
        System.out.println("调用方法之后");
    }

}

最后：通过学生去动态实现相关功能

public static void main(String[] args) {
    PenInterface penInterface = new StudentHand();
    PenInterface student = (PenInterface) new StudentProxy(penInterface).getInstance();
    student.draw();
    //student.write();
}