Using == with String object references

Question

Hi,
I understand that using the == operator to compare two String object references in Java will yield false for two different object references even when the contents are the same, and that you are supposed to use the method .equals() instead. However, in my program the == operator actually works for two different object references that point to the same object since it yields true! I don't understand why it works in my program when it shouldn't. Does someone know why?
Thanks!

Answer 1

overrule. wrote:
warnerja wrote:
... unless some sneaky thread jumps in and changes the a or b reference right before the expression (a == b) were evaluated. This would also assume a or b had greater scope than simply local method variables that only one thread could access.
Just being a nitpickCould you provide an example of how that "greater scope" may look like in this case.
* Greater scope.
* @author Cynthia G.
* @see http://forums.sun.com/thread.jspa?messageID=10520796
public class ObjectAssignmentTest {
  static Object a; // outer scope: class variable
  static Object b; // outer scope: class variable
  public static void main(String[] args) throws InterruptedException {
    a = new Object();
    b = a;
    new Thread(new Runnable() {
      public void run() { ObjectAssignmentTest.b = new Object(); }
    }).start();
    System.out.println(a == b ? "equal" : "not equal");
}For the record, this code is not even guaranteed to make the objects unequal with == before their equality is tested; both threads may go in parallel, the main thread first or the modifying thread first!
s