通过 Cloneable 接口可以很轻松地实现 Java 对象的克隆，只需要 implements Cloneable 并实现 Object 的 clone() 方法即可

public class User implements Cloneable{
    private String username;

    private String password;
    public User(String username, String password) {
        super();
        this.username = username;
        this.password = password;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
    @Override
    public boolean equals(Object obj) {
        User user = (User) obj;
        if (username.equals(user.username) && password.equals(user.password)) {
            return true;
        }
        return false;
    }

}

从源码注释中可以看出，需要实现 Object 类中的 clone() 方法（注意：clone() 函数是一个 native 方法，同时抛出了一个异常）：

https://howtodoinjava.com/core-java/cloning/a-guide-to-object-cloning-in-java/

So deep cloning requires satisfaction of following rules.

• No need to separately copy primitives.
• All the member classes in original class should support cloning and in clone method of original class in context should call super.clone() on all member classes.
• If any member class does not support cloning then in clone method, one must create a new instance of that member class and copy all its attributes one by one to new member class object. This new member class object will be set in cloned object.

https://howtodoinjava.com/core-java/cloning/a-guide-to-object-cloning-in-java/

http://blog.csdn.net/zhangjg\_blog/article/details/18369201