Why isn't .equals recognizing my variable as the same string that I'm passing it?

Question

So this little function is supposed to check if parentheses and brackets are matched next to each other. I feel like it should work and I've tried it a few different ways but I can't figure out how to check if my next char is what I expect it to be.

class Parenths {
    public boolean isValid(String s) {
        char[] parens = s.toCharArray();
        if (parens.length == 0) return true;
        for (int i = 0; i < parens.length; i+=2) {
            String curr= String.valueOf(parens[i]);
            String next = String.valueOf(parens[i+1]);
            // System.out.println(next.equals(")");      --------> false
            // System.out.println(Object.equals(next, ")")); ----> error
            switch (curr) {
                case "(": if (!next.equals(")")) return false;
                case "{": if (!next.equals("}")) return false;
                case "[": if (!next.equals("]")) return false;       
            }
        }
        return true;
    }
}

You can see the lines I printed to debug and it seems that .equals is not the right thing to use here? Can anyone explain why this isn't working?

PS. I realize I don't have to convert the string to a char array to compare elements, so unless that's the only fix, please don't point that out to me.

Answer 1

Not tested, but it seems to be a problem of fall through. Try to replace if (boolean) return boolean with return boolean, this should do the trick.

The problem is that you don't have a break at the end of the cases, so if, for example, your first case is true, it will not stop execution and execute the 2nd test, which will be false. If you change your conditional statements to a direct return, you will not have this problem.

EDIT: Sorry, I read too quickly. Doing so will break your loop. Actually, you have to add a break at the end of the cases.

                case "(": if (!next.equals(")")) return false; break;
                case "{": if (!next.equals("}")) return false; break;
                case "[": if (!next.equals("]")) return false; break;

Answer 2

First , you have to add break; after the cases its important to stop seeing the cases

 switch (curr) {
            case "(": if (!next.equals(")")) return false;
            break;
            case "{": if (!next.equals("}")) return false;
            break;
            case "[": if (!next.equals("]")) return false;   
            break;
        }

Secondly , your code doesnt support the confrotation of a closing patenthesis at first , you have to add a default case

           switch (curr) {
                case "(": if (!next.equals(")")) return false;
                break;
                case "{": if (!next.equals("}")) return false;
                break;
                case "[": if (!next.equals("]")) return false;    
                break;
                default :
                    break;
            }
            return true;

Also , you have to make sure the next element is not null before comparing to it , and dont increment with 2 , you give a String with a one element and that's why you get the error

public static boolean isValid(String s) {
        char[] parens = s.toCharArray();
        if (parens.length == 0) return true;
        for (int i = 0; i < parens.length; i++) {
            String curr= String.valueOf(parens[i]);
            String next = "";
            try { 
            next = String.valueOf(parens[i+1]); 

            switch (curr) {
                case "(": if (!next.equals(")")) return false;
                break;
                case "{": if (!next.equals("}")) return false;
                break;
                case "[": if (!next.equals("]")) return false;    
                break;
                default :
                    break;
            }
            return true;
        }catch(Exception e) {}
            }
        return false;
    }

---

• Test :

    System.out.println(isValid("()"));
    // Output : true
    System.out.println(isValid("("));
    // Output : false