Java .contains cannot be used with charAt

Question

java: incompatible types: char cannot be converted to java.lang.CharSequence

boolean checkParentheses(String str) {
    Deque<Character> stack = new ArrayDeque<>();  

    String k = "({[";
    String s = ")]}";
    for (int i = 0; i < str.length();i++ ) {
        if (k.contains(str.charAt(i))) {
            stack.push(str.charAt(i));
        } else if (s.contains(str.charAt(i))) {

            if (matching(stack.peek()) == str.charAt(i)) {
                return true;
            }
        } else {
            return false;
        }
    }
}

what should I use instead of contains?

`k.contains(str.charAt(i)` there is no `String.contains` that accept a char — Juan Carlos Mendoza, Jan 08 '18 at 14:55
maybe you should ask: what should I use instead of str.charAt(i). try s.contains(String.valueOf(str.charAt(i)) — Stultuske, Jan 08 '18 at 14:55
Try using indexOf instead of contains. Contains requires a String (AKA CharSequence), but you have a char. Also you can refer : https://javamanikandan.blogspot.in/2018/01/java-string-indexof-method-example.html — Mani, Jan 08 '18 at 14:55

gil.fernandes · Accepted Answer · 2018-01-08T15:07:33.377

indexOf with -1.

Something along these lines:

boolean checkParentheses(String str) {
    Deque<Character> stack = new ArrayDeque<>();

    String k = "({[";
    String s = ")]}";
    for (int i = 0; i < str.length();i++ ) {
        if (k.indexOf(str.charAt(i)) > -1) {
            stack.push(str.charAt(i));
        } else if (s.indexOf(str.charAt(i)) > -1) {

            if (matching(stack.peek()) == str.charAt(i)) {
                return true;
            }
        } else {
            return false;
        }
    }
    return false;
}

You could also use contains creating a new String. But that option is not that good (more ineficcient).

2nd option:

boolean checkParentheses(String str) {
    Deque<Character> stack = new ArrayDeque<>();

    String k = "({[";
    String s = ")]}";
    for (int i = 0; i < str.length(); i++) {
        if (k.contains(String.valueOf(str.charAt(i)))) {
            stack.push(str.charAt(i));
        } else if (s.contains(String.valueOf(str.charAt(i)))) {

            if (matching(stack.peek()) == str.charAt(i)) {
                return true;
            }
        } else{
            return false;
        }
    }
    return false;
}

The second option is rather ugly.

Thanks a lot for your help. I've a new error in the if statement containing "matching". Should I create a new question for that? https://pastebin.com/mXzULxn4 — Netizen110, Jan 08 '18 at 15:27

score 0 · Answer 2 · answered Jan 08 '18 at 14:58

Try using indexOf instead of contains. Contains requires a String (AKA CharSequence), but you have a char. Also you can refer : https://javamanikandan.blogspot.in/2018/01/java-string-indexof-method-example.html and https://javamanikandan.blogspot.in/2018/01/java-string-contains-method-explained.html

score 0 · Answer 3 · answered Jan 08 '18 at 15:00

0

Try this

k.contains(""+str.charAt(i))

the method contains works with String objects not Char

answered Jan 08 '18 at 15:00

Mohamed Ali Ben Thaier

68
8

Java .contains cannot be used with charAt

3 Answers3