simple java calculator help needed

Question

So basically, I'm trying to create a simple java calculator for the following functions but it seems my functions are not executing the way they're supposed (i.e. + not adding, - not subtracting). Would appreciate some help :)

    if (ope == "+") {
        //add
    } else if (ope == "-") {
        //subtract
    } else if (ope == "*") {
        //multiply
    } else if (ope == "/") {
        //divide
    }
}

(Also, please read http://tinyurl.com/so-list and http://tinyurl.com/so-hints) — Jon Skeet, Jun 27 '13 at 10:20
Use the equals() method to compare the strings instead of '==' — Siva, Jun 27 '13 at 10:22
Stack Overflow is collaboratively edited. If you have a problem with your question being edited, Stack Overflow may not be the place for you. — Martijn Pieters, Jun 27 '13 at 15:38

score 5 · Answer 1 · answered Jun 27 '13 at 10:20

5

Incorrect String comparison, instead of:

if (ope == "+") {
} else if (ope == "-") {
} else if (ope == "*") {
} else if (ope == "/") {

you should have:

if ("+".equals(ope)) {
} else if ("-".equals(ope)) {
} else if ("*".equals(ope)) {
} else if ("/".equals(ope)) {

answered Jun 27 '13 at 10:20

Adam Siemion

15,569
7
58
92

Thanks Adam, that fixed the operation problems although it seems after the first run (which is correct) any other operation after that gives invalid outputs..would you happen to know where the source of this problem is? edit: seems it might be to do with the clear function, not sure what it is causing it :S – Ted Jun 27 '13 at 10:29

score 0 · Answer 2 · edited May 23 '17 at 11:56

0

In Java SE 7 and later, you can use a String object in the switch statement's expression. More info

if(ope != null)
{
 switch(ope)
 {
  case "+" : do1(); break;
  case "-" : do2(); break;
  case "*" : do3(); break;
  case "/" : do4(); break;
  default :  doDefault(); break;
 }
}

More info about String comparison

edited May 23 '17 at 11:56

Community

1
1

answered Jun 27 '13 at 10:26

Petros Tsialiamanis

2,718
2
23
35

I personally hate this feature because it leads to hardcoded values. It is much better to define the possible values in an "enum" and they can also be used in the switch statement (and checked by the compiler) – Esteve Jun 27 '13 at 10:34

simple java calculator help needed

2 Answers2