Question

If I have a piece of code like this:

MyClass[] objArray = new MyClass[7];
//assign values to objArray
//do something here
//sometime later
MyClass newObj = new MyClass();
objArray[3] = newObj;

The last statement above will do the following:

• copy all the contents of the newObj to the space referred to by objArray[3].

Questions

1. Am I right?

2. Shallow copy or deep copy?

3. If it is shallow copy, how can I make the deep copy possible?

   objArray[3] = newObj; 
   

4. Does this rule applies to other Java container types, such as Queue, List, …?

Answer 1

Answer 1&2: No. Only a reference to the object is copied. newObj and objArray[3] will afterwards refer to the same object instance.

Answer 3: If you want a copy, you have to implement it yourself. You could implement a copy constructor or Clonable, or for a simple deep copy, serialize and deserialize the object, but that requires it and all objects it consists of to be Serializable

Answer 4: It’s exactly the same for all Java Objects: the reside on the heap, and the code works only with references to the objects. Container types usually implement a copy constructor that does a shallow copy. There is no deep copy functionality that is automatically available for all classes.