Java skipping if-statement

Question

The method below takes a string and a pattern and returns true if they match. A '.' matches 1 char, and '*' matches 0 or more (for example, expMatch("abc", "a.c")should return true). I added some print statements to see where I made a mistake, and it seems like the if statement is skipped, even if str.length() == 1.

I call it System.out.println(expMatch("abc", "a*c"));

Here is the code:

public static boolean expMatch(String str, String pat)
{   
    if (str.charAt(0) == pat.charAt(0) || pat.charAt(0) == '.')
    {
        System.out.println("in if");
        System.out.println(str.charAt(0));
        System.out.println(pat.charAt(0));
        System.out.println(str.length());
        if (str.length() == 1)
            return true;
        expMatch(str.substring(1), pat.substring(1));
    }

    else if (pat.charAt(0) == '*')
    {   
        System.out.println("in else");
        System.out.println(str.charAt(0));
        System.out.println(pat.charAt(0));
        if (str.length() == 1)
            return true;
        if (str.charAt(0) == pat.charAt(1)) //val of * = 0
            expMatch(str, pat.substring(1));
        else if (str.charAt(1) ==pat.charAt(1))
            expMatch(str.substring(1), pat.substring(1));           
    }

    return false;           
}

and output:

in if
a
a
3
in else
b
*
in if
c
c
1
false

Even if the length is 1, does it skip if? Any idea why? Postscript I am not looking for a solution, just why the if statement is skipped.

Answer 1

, , . :

System.out.println(expMatch("abddddc", "a*c"));

, * , , "" .

, -, if. ( , , , , , , ). . :

System.out.println(expMatch("adddcac", "a*c")); 
// the * needs to eat dddca (despite the c present in dddca),  
// it should not stop recursing there at that c  

, - . if while .

. . , ( , ). 100%, .

public class Test055 {

    public static void main(String[] args) {
        // System.out.println(expMatch("abddddc", "a*c"));

        System.out.println(expMatch("adcax", "a*c"));
        System.out.println(expMatch("adcax", "a*c*"));

        System.out.println(expMatch("adcacm", "*"));
        System.out.println(expMatch("adcacmmm", "a*c"));
        System.out.println(expMatch("adcacmmmc", "a*c"));
        System.out.println(expMatch("adcac", "a*c"));

        System.out.println(expMatch("adcacxb", "a*c.b"));
        System.out.println(expMatch("adcacyyb", "a*c.b"));
        System.out.println(expMatch("adcacyyb", "a*c*b"));

    }

    public static boolean expMatch(String str, String pat)
    {
        // System.out.println("=====================");
        // System.out.println("str=" + str);
        // System.out.println("pat=" + pat);

        if (pat.length() == 0 && str.length() > 0) {
            return false;
        } else if (pat.length() == 0 && str.length() == 0) {
            return true;
        } else if (pat.charAt(0) == '.'){
            return str.length() >= 1 && expMatch(str.substring(1), pat.substring(1));
        }else if (pat.charAt(0) != '*'){
            return str.length() >= 1 && pat.charAt(0) == str.charAt(0) && expMatch(str.substring(1), pat.substring(1));
        }else{
            // Now let handle the tricky part

            // (1) Look for the 1st non-star in pattern
            int k=-1;
            char ch = ' ';
            for (int i=0; i<pat.length(); i++){
                if (pat.charAt(i) != '*'){
                    k = i;
                    ch = pat.charAt(k);
                    break;
                }
            }

            if (k==-1){
                // (2A) only stars found in pattern, OK, any str matches that
                return true;
            }else{
                // (2B) do full search now checking all  
                // possible candidate chars in str that 
                // match the char ch from pattern
                for (int i=0; i<str.length(); i++){
                    if (str.charAt(i)==ch){
                        boolean b = expMatch(str.substring(i+1), pat.substring(k+1));
                        if (b) return true;
                    }
                }
                return false;
            }
        }
    }
}

Answer 2

false . expmatch , . , , recurses ( 1) return, false.

Answer 3

expMatch(), false return false;

:

• expMatch() .
• if
• if expMatch()
• else
• else expMatch()
• if
• you leave the expMatch () method
• you will leave another expMatch method
• false returns