Switch error: incompatible type found

[Zahir Sercan]

Hi Java buddies,

Im building a expression tree calculator. Im now stuck with a problem here is the code snippet.

Method Postfix

public String Postfix() {
        String res = " ";
        if (this.left != null) {
            res += this.left.Postfix() + " ";
            res += this.right.Postfix() + " ";
        }
        res += this.Value;
        return res;
    }

Methode Solve

public int Solve() {
        String a, b;


        String[] tokens = Postfix().split(" ");
        for (String e : tokens) {

            //byte, char, short of int
            switch(e) { //At this point i get an error: incompatible types; found   : java.lang.String;  required: int
                case "+":
                    b = stack.pop();
                    a = stack.pop();
                    stack.push(Integer.toString(Integer.parseInt(a) + Integer.parseInt(b)));
                    break;
                case "-":
                    b = stack.pop();
                    a = stack.pop();
                    stack.push(Integer.toString(Integer.parseInt(a) - Integer.parseInt(b)));
                    break;
                case "/":
                    b = stack.pop();
                    a = stack.pop();
                    stack.push(Integer.toString(Integer.parseInt(a) / Integer.parseInt(b)));
                    break;
                case "*":
                    b = stack.pop();
                    a = stack.pop();
                    stack.push(Integer.toString(Integer.parseInt(a) * Integer.parseInt(b)));
                    break;
                case "%":
                    b = stack.pop();
                    a = stack.pop();
                    stack.push(Integer.toString(Integer.parseInt(a) % Integer.parseInt(b)));
                    break;
                default:
                    stack.push(e);
                    System.out.println(stack.pop());
                    break;
            }

        }
        return Integer.parseInt(stack.pop());
        //return 1;
    }

Any idea or advice what i can do to solve this problem?

Cheers

[Mohamed Sanaulla]

Unless you are using Java 7, you cannot use Switch with Strings. You should be using compile time constants to compare in the case.

[Campbell Ritchie]

You might do better to split on "\\s+" unless you are sure you always have single spalces.

[dennis deems]

You can switch on an enum, and an enum constant can hold a String value.

[Jeff Verdegan]

Mohamed Sanaulla wrote:Unless you are using Java 7, you cannot use Switch with Strings. You should be using compile time constants to compare in the case.

Doesn't the String switching require compile-time constants as well? That is:

final String x = "abc";
String y = bufferedReader.readLine();

// good
switch (x) {...}

// bad
switch (y) {...}

Or am I just making baseless assumptions?

[Mohamed Sanaulla]

Jeff Verdegan wrote:

Mohamed Sanaulla wrote:Unless you are using Java 7, you cannot use Switch with Strings. You should be using compile time constants to compare in the case.

Doesn't the String switching require compile-time constants as well? That is:

final String x = "abc";
String y = bufferedReader.readLine();

// good
switch (x) {...}

// bad
switch (y) {...}

Or am I just making baseless assumptions?

I dont know if any one approach is recommended. But both of them work though.