clone() - shallow or deep?

[David Duran]

According to the HashMap javadoc, the clone() method does a shallow copy only, the keys and values are not cloned. If that is the case, why is it that the key in the cloned object below is maintained:

HashMap m = new HashMap();
m.put("hello", "world");
        
HashMap mClone = (HashMap)m.clone();
m.remove("hello");
        
System.out.println(m.get("hello") + ", " + mClone.get("hello"));

The result is: null, world
If the keys and values were not supposed to be cloned, then shouldn't the result be: null, null?

[Thomas Paul]

A shallow copy means the HashMap has been copied but not the objects in the HashMap. So adding and removing from one HashMap does not cause changes to the clone. Try this. Create a Button and set it's text to "OK". Put the Button in a HashMap. Clone the HashMap. Change the Button's text in one HashMap to "Cancel". Compare the text of Button in each HashMap. What do you think you will find?