Object References as Parameters

Object references can be parameters. Call by value is used, but now the value is an object reference. Since the invoked method has a reference to an object, it can access that object and possibly change it. Here is an example program:

class ObjectPrinter
{
  public void print( String st )
  {
    System.out.println("Value of parameter: " + st );    
  }
}

class OPTester
{
  public static void main ( String[] args )
  {
    String message = "Only One Object" ;

    ObjectPrinter op = new ObjectPrinter();

    System.out.println("First  value of message: " + message );    
    op.print( message );
    System.out.println("Second value of message: " + message );    
  }
}

In this program, the local variable message contains a reference to a String object. A copy of that reference is made in the formal parameter st of the print() method. The object is not copied.