access private member

[Lee Xu]

I know that the object can access the private member of another object of the same class, but forget the example. Can someone give an example on this? Thanks

[Junaid Bhatra]

Acess restrictions apply at the class level, and not at the object level. The following is a trivial example, but it illustrates the point.

class Foo
{
  private int i;
  public void aMethod()
  {
    Foo foo = new Foo();
    foo.i = 5; //legal    
  }
}

[Anthony Villanueva]

public class Test
{ 
public static void main(String args[])
{
Thingamajig g = new Thingamajig("Gizmo");
Thingamajig w = new Thingamajig("Widget");
g.getOtherThingy(w);
w.getOtherThingy(g);
}
} 
class Thingamajig
{
private String Thingy;
Thingamajig(String t)
{
Thingy = t;
} 
void getOtherThingy(Thingamajig t)
{
System.out.println(t.Thingy);
}
}

[Lee Xu]

Thanks for prompt reply. I think there is a better example, but I cannot recall.

[Frank Carver]

The most popular use of this behaviour is in the "equals" method. All classes have one, even if the just inherit the default one from Object, and a sensible "equals" method is vital to allow your class to be put into Collections.
A typical class with an explicit "equals" might look like:

class Thing
{
 private String message = null;
 
 public void init(String message)
 {
  this.message message;
 }
 public boolean equals(Object obj)
 {
  boolean ret = false;
  if (obj instanceof Thing)
  {
    Thing that = (Thing)obj;
    ret = (this.message == null && that.message == null) ||
          this.message.equals(that.message);
  }
  return ret;
 }
}

Without access to the private members of the supplied Thing it would be much harder to write a reasonable "equals" method.

[Dan Chisholm]

Lee,
If you are looking for an example of why it is necessary to allow objects of the same class to access one anothers private members, then I think that Frank's example is excellent. If you are looking for a simplistic example that illustrates that objects of the same class can indeed access one another's private methods, then the following might be helpful.

class A {
  private String s;
  private A(String s) {this.s = s;}
  public static void main (String[] args) {
    A a1 = new A("A1");
    A a2 = new A("A2");
    A a3 = new A("A3");
    // Access private members of objects a1, a2, a3.
    System.out.print(a1.s+","+a2.s+","+a3.s);
  }
}

[Lee Xu]

Dan and Frank,
Thanks. I got it.
Lee