Checking if an array has a certain character, why is my code not working?

Question

Hello here is some code to check for a valid character, although the code is not working. Even if 'operand' is a valid character it will never print yes, and return false. No matter what even if the character is valid it just doesn't recognize it and always goes to the else statement. Please help!

public static boolean checkValidOperands(char operand) {

    char[] validOperators = {'+', '-', '*', '/', 'q'};
    List<char[]> validOp = Arrays.asList(validOperators);
    if (validOp.contains(operand))  {
        System.out.println("Yes");
        return false;
    }  else {
        System.out.println("Please enter valid operand");
        return true;
    }
}

See this question: http://stackoverflow.com/questions/1248763/arrays-aslist-of-an-array Edit: Or @Reimeus answer — jonvuri, Mar 01 '13 at 02:50
Are you sure the declaration for validOp shouldn't be a List rather than a List? You're not looking for a list of character *arrays*, but just characters... — David W, Mar 01 '13 at 02:51
Yup looks like this is the problem, I tried List but is not recognized... — Nearpoint, Mar 01 '13 at 02:54

score 7 · Accepted Answer · answered Mar 01 '13 at 02:50

7

You could use:

List<Character> validOp = Arrays.asList('+', '-', '*', '/', 'q');

answered Mar 01 '13 at 02:50

Reimeus

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score 2 · Answer 2 · edited May 23 '17 at 11:50

The way you are creating a list of characters is wrong.

In your current code the list that you made is actually a list of character arrays, instead of characters.

import java.util.Arrays;
import java.util.List;

public class Test{
    public static void main(String[] args){
    char ch = '+';
    System.out.println(checkValidOperands(ch));

    }

    public static boolean checkValidOperands(char operand) {

        Character[] validOperators = {'+', '-', '*', '/', 'q'};
        List<Character> validOp = Arrays.asList(validOperators);
        if (validOp.contains(operand))  {
            System.out.println("Yes");
            return false;
        }  else {
            System.out.println("Please enter valid operand");
            return true;
        }
    }
}

PS: Also for future, do not use List<char>, List<int> etc.. as you cannot use a primitive type for generic in Java. Use their corresponding Object counter parts instead. Refer to this question for more information Why can Java Collections not directly store Primitives types?

score 0 · Answer 3 · answered Mar 30 '15 at 17:00

0

A string is a better data structure for a set of characters. For example,

String validOperators = "+-*/q";

if (validOperators.indexOf(operand) != -1)  {
    System.out.println("Yes");
    return false;
}

answered Mar 30 '15 at 17:00

John Henckel

10,274
3
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Checking if an array has a certain character, why is my code not working?

3 Answers3