How to check if String contains only operators?

Question

code:

 public void convertString(String s){
    String[] arr = s.split("");


    for (int i = 0; i < arr.length ; i++) {
        stringStack.push(arr[i]);
    }
    
     if (stringStack.peek().matches("[0-9]+")){
         digitStack.push(Double.valueOf(stringStack.pop()));
     }else if (stringStack.peek().matches("[(+=-*/^)]+")){

     }

     System.out.println(digitStack);

}

in this line "[(+=-*/^)]+" a receive error:

Illegal character range (to < from)

How to check if String contains only operators?

Not related to the question, but you might want to add `%` as the mod operator. — ZephDavies, Nov 09 '20 at 10:24

score 1 · Accepted Answer · edited Nov 09 '20 at 10:38

1

- in [ ] has a special meaning, e.g. [0-9].

Add an escape character, and it should work. [(+=\-*/^)]+

edited Nov 09 '20 at 10:38

MC Emperor

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answered Nov 09 '20 at 10:15

Zen

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An alternative may be to put the dash to the end of the character class. In my opinion, it'll make it a little bit more readable. – MC Emperor Nov 09 '20 at 10:17
The OP use `( )` to capture groups, in this case add dash to start or end may not works. – Zen Nov 09 '20 at 10:21
I'm not use ( ) to capture groups, it's put in matches() method – Dartweiler Nov 09 '20 at 10:23
You can put `-` at the beginning to make it lose special meaning, so you don't need to escape it -- `[-(+=*/^)]+` – Nikolai Shevchenko Nov 09 '20 at 11:37

score 0 · Answer 2 · answered Nov 09 '20 at 10:42

You have actually two options:

Escape the dash with a backslash (\- instead of -). That'll instruct the regex engine to parse the dash as a literal dash, instead of a range divider. This is what Zen already mentioned.
The second option is to put the dash at the beginning or at the end of the character class. If the dash is place in either, then the regex engine knows that the dash is not part of a character range.
```
[(+=*/^)-]
```

How to check if String contains only operators?

2 Answers2