Question

How are primitive and reference types different an examples of how copying works differently for these two types.

Answer 1

Primitives vs. References

• primitive types are the basic types of data
  • byte, short, int, long, float, double, boolean, char
  • primitive variables store primitive values
• reference types are any instantiable class as well as arrays
  • String, Scanner, Random, Die, int[], String[], or any objects.
  • reference variables store addresses

Assignment

• copies the contents of RHS variable into LHS variable
  • primitives: the primitive value is copied
  • references: the address is copied
• implications: for references the object is not copied, it is shared (reference variables are aliases)

Example

• primitive types
  • int x = 10;
  • int y=x;

This above statement copies the value stored in x(that is 10) to y.

• reference types
  • int x[] = {1,2,3,4,5};
  • int y[] = x;
  • y[3] = 7;

The above statement assigns the array x to values {1,2,3,4,5} and then we copy y[] = x, this does not copy the entire array but y is given as a reference of the memory represented by x.

So in the next line when we assign y[2] = 7, it is also reflected in x as we are using the same memory for both the arrays. Generally programming languages comes with specific utilities if we need to copy the values in the array.

If we print x[] and y[] after the y[2]=7 statement, we will find both x and y are same.