java passing variables by reference?

[Nikos Stavros]

is there a way to do this in java, like the following c++ code

  // passing parameters by reference
#include <iostream>
using namespace std;
 
void duplicate (int& a, int& b, int& c)
{
  a*=2;
  b*=2;
  c*=2;
}
 
int main ()
{
  int x=1, y=3, z=7;
  duplicate (x, y, z);
  cout << "x=" << x << ", y=" << y << ", z=" << z;
  return 0;
}  

[William Brogden]

Not the way you coded it. If you want to manipulate a bunch of int primitives and return the values, pass an array of int (a reference to an array object.)
Bill

[Joanne Neal]

As you are using a single method to process three ints, then we can assume those three ints are related in some way. If that is the case then they should be in a class.

class ThreeInts
{
  private int a;
  private int b;
  private int c;
 
  public ThreeInts(int a, int b, int c)
  {
    this.a = a;
    this.b = b;
    this.c = c;
  }
 
  public int getA()
  {
    return a;
  }
 
  public int getB()
  {
    return b;
  }
 
  public int getC()
  {
    return c;
  }
}

This class should have a method called duplicate (double would be a better name) that doubles the value of each of the ints

public void duplicate()
{
  a *= 2;
  b *= 2;
  c *= 2;
}

Then your main method looks like this

public static void main(String args[])
{
  ThreeInts ti = new ThreeInts(1, 3, 7);
  ti.duplicate();
  System.out.println("a = " + ti.getA() + ", b = " + ti.getB() + ", c = " + ti.getC());
}

If the three ints are not related in any way, then it is probably a bad design to have a single method processing them.
[ August 15, 2006: Message edited by: Joanne Neal ]

[Rusty Shackleford]

No you can't do that. Everything in Java is passed by value.

[Ilja Preuss]

While William's solution using an array would work, I find it to be a rather awkward workaround.

A goal of OO design is to put the data, and the operations on the data together in a class. Joanne's solution is one of the possible ways to do that.