clone() method in Java

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再見小時候
再見小時候 2021-02-14 22:14

as I understood, the method clone() gives us the ability to copy object (no refernce) in Java. But I also read, that the copy is shallow. So what the point? Which a

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  •  醉梦人生
    2021-02-14 23:09

    The difference is that you can modify the cloned object without modifying the original object.

    Point p = new Point(1,2);
    Point p2 = p.clone();
    Point p3 = p;
    p2.x = 5;
    p3.y = 7;
    

    The change on p3 does feed back to p, while the change on p2 does not.

    Let's see how the situation is after the individual statements (assuming 1, 2, 5, 7 would be objects):

    Point p = new Point(1,2);
    
                .-----.    .-----.
     p  ----->  |  x -+--> |  1  |
                |     |    '-----'
                |     |    .-----.
                |  y -+--> |  2  |
                '-----'    '-----'
    
    
    Point p2 = p.clone();
    
                .-----.    .-----.    .-----.
     p  ----->  |  x -+--> |  1  | <--+- x  |  <----- p2
                |     |    '-----'    |     |
                |     |    .-----.    |     |
                |  y -+--> |  2  | <--+- y  |
                '-----'    '-----'    '-----'
    
    Point p3 = p;
    
                .-----.    .-----.    .-----.
     p  ----->  |  x -+--> |  1  | <--+- x  |  <----- p2
                |     |    '-----'    |     |
                |     |    .-----.    |     |
     p3 ----->  |  y -+--> |  2  | <--+- y  |
                '-----'    '-----'    '-----'
    
    
    p2.x = 5;
    
                .-----.    .-----.    .-----.    .-----.
     p  ----->  |  x -+--> |  1  |    |  x -+--> |  5  |
                |     |    '-----'    |     |    '-----'
                |     |    .-----.    |     |
     p3 ----->  |  y -+--> |  2  | <--+- y  |  <----- p2
                '-----'    '-----'    '-----'
    
    
    p3.y = 7;
    
                .-----.    .-----.    .-----.    .-----.
     p  ----->  |  x -+--> |  1  |    |  x -+--> |  5  |
                |     |    '-----'    |     |    '-----'
                |     |    .-----.    |     |
     p3 ----->  |  y  |    |  2  | <--+- y  |  <----- p2
                '--+--'    '-----'    '-----'
                   |     .-----.
                   '---> |  7  |
                         '-----'
    

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