Not sure what i've done wrong

Question

The problem is to allow a user to input 2 numbers... then allow the user to choose the mathematical operation performed. Ive used if statements but it seems after you chose what operation you want to use it skips the if statements and goes straight to the answer... which is always 0. any help is appreciated.
import javax.swing.JOptionPane;
public class Calculate1
public static void main(String args[])
     int number1=0, number2=0, answer=0, choice1;
     String num1, num2, choice;     
     //Input Dialog boxes
num1=JOptionPane.showInputDialog(null,
     "Enter the first number: ", "First number",
     JOptionPane.QUESTION_MESSAGE);
     num2=JOptionPane.showInputDialog(null,
     "Enter the second number: ", "Second number",
     JOptionPane.QUESTION_MESSAGE);
     //Convert values from string to int
     number1=Integer.parseInt(num1);
     number2=Integer.parseInt(num2);
     //Math operation input box
     choice=JOptionPane.showInputDialog
          ("To add your numbers, press A" +
          " \nTo subtract your numbers, press S" +
          " \nTo multiple your numbers, press M");
     if (choice == "a")
     answer = number1 + number2;
     else if (choice == "s")
     answer = number1 - number2;
     else if (choice == "m")
     answer = number1 * number2;
     // Answer statement to screen
JOptionPane.showMessageDialog(null,
     "Your answer is " + answer, "Your answer",
          JOptionPane.INFORMATION_MESSAGE);
System.exit (0);

Answer 1

to illustrate aegons' reply, see this code
public class TestStrings {
public static void main(String[] args) {
  String test = args.length == 0 ? "TEST" : args[0];
  System.out.println("TEST".equals(test));
  System.out.println("TEST" == test);
}this code here i haven't compiled nor run.
but i assume that if you start it the way java TestStrings TEST, then it prints out:
true
false
but if you run it without first parameter "TEST", then it might even print out:
true
true
since internaly that "TEST" and variable test have pointers to the same memory region.
but now if you run it with first parameter other than "TRUE", then it prints out:
false
false
(which shouldn't surprise you)
now there was a place where equation check with == could return true, that might seem convenient way for checking strings, but really it's not, because it works as we might excpect it, only with some JRE implementations and only in test programs that are quite small and hardcoded...
i'm telling that because i don't want others to go wander off from their dayjob only because some sample programms make it look like they had implemented some fancy == handling in newer JRE/SDK
(maybe it was interesting....)