适配器

public class IntegerDemo {
	public static void main(String[] args) {
		UserDao ud = new UserDaoImp();
		ud.add();
	}
}

interface UserDao {// 接口
	public abstract void add();

	public abstract void delete();

	public abstract void update();

	public abstract void find();
}

abstract class UserAdapter implements UserDao {// 抽象类
	public void add() {
	}

	public void delete() {
	}

	public void update() {
	}

	public void find() {
	}
}

class UserDaoImp extends UserAdapter {// 实现类
	public void add() {// 重写
		System.out.println("add");
	}
}