Problem Finding Index Value of a String in Array

[Scott Kamen]

I'm working on a class method that will accept a string array and a string. It then loops to see if that string value matches any of the strings in the array and if it does then it returns the index value of the string in the array that it matches. If the string that is given to the method can't be found in the array then it's supposed to return a -1. This is a pat of a larger project as a whole but this is the part that's causing the problems. I keep getting told by the compiler that I need a return statement even though it appears that I have that covered. There is probably someway the exit the method w/ out going through the return statement which is why I'm getting the error but I just can't figure it out and it's been driving me crazy. Here is the code:

public static int find (String[] array , String name) {
   
   // For loop to determine index value of string object , the loop is continued
   // until 3 instead of 2 because you know that when you hit the index value of 3
   // that the name is not going to be found because with the 3 element array the
   // maximum array value would be 2
   for (int i=0; i<=3; i++ ) {
     if (array[i].equals(name)) { 
       return i;
     }
     else {
       if (i==3) {
         return -1;
       }
     }
   }
}

I could have something completley offball or wrong here but I just can't seem to figure it out.
thanks,
-Scott

[Phil Chuang]

the problem is that you don't have a return for every branch:
if () return i
else
if () return -1;
// you need a return right here
// or an plain else branch with a return
Quick fix solution: get rid of the "if (i==3)" part.

[Jim Yingst]

The compiler is not quite smart enough to do the analysis that would be required to determine that your code is guaranteed to return. It sees

       if (i==3) {
         return -1;
       }

and thinks, well, if i != 3, this won't return, so the code isn't guaranteed to eventually returned. Yeah, we know that the loop will continue until eventually i == 3, but the compiler doesn't see that.
In fact your code is a bit more complex than necessary here. Try deleting the else {} clause entirely and study exactly what would happen when i == 3, and then i == 4. It's possible to add a single return statement in the appropriate location, that will solve your problem.
Incidentally, this whole method could also be coded as:

    public static int find (String[] array , String name) {
      return Arrays.asList(array).indexOf(name);
    }

Don't worry about this if you haven't dealt with Collections yet - but it's worth delving into them eventually.

[Scott Kamen]

Thanks for the quick help but I'm still having some trouble. Phil , If I got rid of the (i==3) wouldn't it return a -1 after the first time through the loop that the strings don't match (which isn't what it's supposed to do)? Also , Jim , I tried your suggestion of getting rid of the entire else {} clause and attempting to think about what happens when i==3 and i==4 but I couldn't make any headway. The second way you proposed writing it looks tempting but It's a bit beyond what I'm doing right now (plus when I tried it in my code it gave me an error about the Arrays variable , would I have to do an import statement in order to get it to work?) so I think I'm going to stick with trying to get it to work with a loop.
thanks again,
-Scott

[William Barnes]

Isn't is a little silly to be checking for "i==3" inside of the 'for' loop?

for (int i=0; i<3; i++ ) 
{
  if (array[i].equals(name)) 
  { 
     return i;
  }
}
return -1 ;

And don't you need to make this just a little more generic?

[Joel McNary]

You're right that simply removing the if(i==3) line would return -1 on the first time through the loop. What you need is to have the return -1 outside the foor loop, as:

public static int find (String[] array , String name) {      
// For loop to determine index value of string object , the loop is continued   
// until 3 instead of 2 because you know that when you hit the index value of 3   
// that the name is not going to be found because with the 3 element array the   
// maximum array value would be 2   
for (int i=0; i<=3; i++ ) {     
if (array[i].equals(name)) {        
return i;     
}     
}
return -1;
}

Also, this method will only tell you if the string is in the first three elements of the array. If the Array is longer than three elements (and the requested string is the fifth element), this method will never find it. And if the array has fewer than three element, you will get an ArrayIndexOutOfBounds exception. Try:

for (int i=0; i<array.length; i++ ) {     

This will loop through the entire array, no matter how long it is.
And, yes, I agree with Jim that learning about Collection is well worth your time. To get Jim's solution to work, you need to import java.util.Arrays

[Scott Kamen]

Thanks a lot. I think at one point I basically had the right idea but I had the return -1 inside of the for loop which was what was causing the problems. The array I'm working w/ is a set wired 3 elements so that is never going to change so I can just use the number 3 but thanks for the help on suggesting a scalable method anyways.
-Scott