AP® Computer Science A glossary
Passing references
Also called: passing objects to methods
Course: AP® Computer Science A Shows up in: Unit 3: Class Creation
When an argument is an object reference, the parameter gets a copy of the reference, so both refer to the same object.
Appears in the course and exam description (CED): 3.6.A.13.6.A.2
Java always passes arguments by value; for an object the value copied is the reference, and no new object is created. Calling a mutator through the parameter changes the caller’s object, but assigning a new object to the parameter does not change the caller’s variable.
public class Box
{
private int size;
public Box(int s)
{
size = s;
}
public static void grow(Box b)
{
b.size++; // changes the caller's object
b = new Box(100); // changes only the parameter
}
public static void main(String[] args)
{
Box mine = new Box(3);
grow(mine);
System.out.println(mine.size);
}
}Output:
4