Thread: Could someone help me with this code?

Though my code compiles, it returns all 0's, and I don't understand why.

The problem I have to answer is :

Given 2 strings, a and b, return the number of the positions where they contain the same length 2 substring. So "xxcaazz" and "xxbaaz" yields 3, since the "xx", "aa", and "az" substrings appear in the same place in both strings.

Example:

stringMatch("xxcaazz", "xxbaaz") → 3
stringMatch("abc", "abc") → 2
stringMatch("abc", "axc") → 0

My code for the method is:

public int stringMatch(String a, String b)
{
int match = 0;
int x = 0;
int y = 2;
while(y < a.length() && y < b.length())
{
if (a.substring(x,y) == b.substring(x,y))
{
match++;
x++;
y++;
}
else
{
x++;
y++;
}
}
return match;
}

Use the equals() method when comparing the contents of two Strings, not the == operator

My bad.

The new code after using the equals method is:

    public int stringMatch(String a, String b) 
    {
        int match = 0;
        int x = 0;
        int y = 2;
        String aa = a.substring(x,y);
        String bb = b.substring(x,y);
        while(y < a.length() && y < b.length())
        {
            if (aa.equals(bb) )
            {
                match++;
                x++;
                y++;
            }
            else
            {
                x++;
                y++;
            }
        }
        return match;
    }

The substrings are supposed to start at the same index.
Thanks for the responses btw!

Does it work now?

It no longer returns all 0s, but I still don't recieve the expected answer.
The tests are:

stringMatch("xxcaazz", "xxbaaz") → expected 3, got 4
stringMatch("abc", "abc") → expected 2, got 1
stringMatch("abc", "axc") → expected 0, got 0
stringMatch("hello", "he") → expected 1, got 0
stringMatch("he", "hello") → expected1, got 0
stringMatch("aabbccdd", "abbbxxd") → expected 1, got 0
stringMatch("aaxxaaxx", "iaxxai") → expected 3, got 0
stringMatch("iaxxai", "aaxxaaxx") → expected 3, got 0

See post #6

The new code is:

public int stringMatch(String a, String b) 
    {
        int match = 0;
        int x = 0;
        int y = 2;
        String aa = a.substring(x,y);
        String bb = b.substring(x,y);
        while(y < a.length() && y < b.length())
        {
            if (aa.equals(bb) )
            {
                match++;
                x++;
                y++;
                aa = a.substring(x,y);
                bb = b.substring(x,y);
            }
            else
            {
                x++;
                y++;
                aa = a.substring(x,y);
                bb = b.substring(x,y);
            }
        }
        return match;
    }

I get more correct answers now, though a few still come out incorrect

stringMatch("xxcaazz", "xxbaaz") → expected 3, got 2
stringMatch("abc", "abc") → expected 2, got 1
stringMatch("abc", "axc") → expected 0, got 0
stringMatch("hello", "he") → expected 1, got 0
stringMatch("he", "hello") → expected1, got 0
stringMatch("aabbccdd", "abbbxxd") → expected 1, got 1
stringMatch("aaxxaaxx", "iaxxai") → expected 3, got 3
stringMatch("iaxxai", "aaxxaaxx") → expected 3, got 3

It helps to print out the values of the Strings that are being compared so you can see what the code is doing.
Add some printlns just before the if test with the equals() to show their values. Something like this:
System.out.println("aa=" + aa +"<");

public int stringMatch(String a, String b) 
    {
        int match = 0;
        int x = 0;
        int y = 2;
        String aa = a.substring(x,y);
        String bb = b.substring(x,y);
        while(y <= a.length() && y <= b.length())
        {
            aa = a.substring(x,y);
            bb = b.substring(x,y);
            if (aa.equals(bb) )
            {
                match++;
                x++;
                y++;
 
            }
            else
            {
                x++;
                y++;
 
            }
        }
        return match;
    }

lol took me a while but I finally got it. My code works everytime unless one of the parameters has less than 2 characters, but I think I know where to go from here. Thanks for the help snowguy and norm, I really appreciate it