Copy a Long object in Java

Question

I think it should be:

Long a = Long.valueOf(0);
Long b = Long.valueOf(1);
Long a = b.clone();

But there is no clone method in Long object...

Maybe Long a = Long.valueOf(b.LongValue()) will work, but it looks dirty. Is there any nice way to handle this?

Answer 1

I think, because Long is immutable, you can just use an assignment.

Long a = (long) 1;
Long b = a;
a = (long) 2;
System.out.printf("a=%d, b=%d%n", a, b);

Output is

a=2, b=1

Answer 2

Something that looks much cleaner in my opinion:

Long a = b.LongValue()

There will be an implicit casting to the boxed value. The b.LongValue() will return the primitive long and it will automatically be boxed into an object of type Long.

You can read about boxing and auto-boxing in this link for more information.

Here's the section that talks about autoboxing of primitives:

Autoboxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object wrapper classes. For example, converting an int to an Integer, a double to a Double, and so on. If the conversion goes the other way, this is called unboxing.

Here is the simplest example of autoboxing:

Character ch = 'a';

Just for the completeness of the question:

• Boxing - The process of taking a primitive and use it in it's wrapper class. Meaning boxing long in Long or int in Integer, etc... You can get a boxed value either by creating a new object of the wrapper class as follows:

  Long boxed = new Long(1);
  

  Or by assigning a primitive to a variable of type of a wrapper class (auto-boxing):

  Long boxed = 1l;
  

• Unboxing - The opposite process of boxing. That's the process of taking a boxed parameter and get its primitive. Either by getValue() or by auto-unboxing as follows:

  Long boxed = new Long(1);
  long unboxed = boxed.getValue();
  

  Or by just assigning a boxed object to a primitive:

  long unboxed = new Long(1);