CODEWITHSUNDEEP
javaarraysstringwhile-loop
user3417291
user3417291

Reputation: 1

java.lang.ArrayIndexOutOfBoundsException: 3 in a while loop

I've been getting this exception and I've no idea how to go about fixing it:

java.lang.ArrayIndexOutOfBoundsException: 3

in the while loop. Here's my code:

public class NameSearch {
    static String[] names = new String[3];

    void populateStringArray() {
        names[0] = "Ben";
        names[1] = "Thor";
        names[2] = "Zoe";
        names[3] = "Kate";
    }

    public static void main(String[] args) {
        String pName;
        int max = 4;
        int current = 1;
        boolean found = false;

        Scanner scan = new Scanner(System.in);
        System.out.println("What player are you looking for?");
        pName = scan.next();
        while (found == false && current <= max) {
            if (names[current] == pName) {
                found = true;
            } else {
                current = current + 1;
            }
        }
        if (found == true) {
            System.out.println("Yes, they have a top score");
        } else {
            System.out.println("No, they do not have a top score");
        }
    }
}

The code is meant to ask the user to input a name and it will check to see if the name is in the array (in a nutshell).

My IDE (Eclipse) says that the error lies in the line if (names[current] == pName){.

Upvotes: 0

Views: 2458

Answers (5)

Trevor Freeman
Trevor Freeman

Reputation: 7232

You are indexing your array elements in the loop between 1 and 4 (inclusive), when you need to be indexing them between 0 and 3 (inclusive).

Change current to start at 0, and max to be 3 and you should be all good.

For perhaps an even better alternative, consider putting your list of names in a HashSet and not needing to iterate at all. E.g.

Set<String> names = new HashSet<String>();
names.add("Ben");
names.add("Thor");
names.add("Zoe");
names.add("Kate");

if (names.contains(pName)) {
//...

If the ordering of the names is important, then you could use a List instead, which also has a contains method (just not generally as efficient as that in a Map implementation.. O(n) vs O(1) typically). If the number of names in your list is small, or performance is not an issue, then it will not matter either way.

Upvotes: 2

cbender
cbender

Reputation: 2251

It's because you have the condition current <= max. If max is 4 then that means current can equal 4 and there is no index 4 in the array. That's why the error comes from names[current], you are trying to access index 4 and it doesn't exist. You should just use < instead of <= or have max = 3 instead of 4.

Side Notes:

  • Because arrays start with an index 0 if current equals 1 when the loop begins it will never look at the first index in the array.
  • When checking the value of a boolean as a condition, instead of doing == true or == false, you can just put the variable for true or add a ! before for false. So in this case instead of while(found == false you can do while(!found.
  • When incrementing an int, instead of current = current + 1, the common practice is to use current++ when incrementing by 1 or += when incrementing by more than 1 (for example current +=2 would increment current by 2).

Upvotes: 2

AlphaModder
AlphaModder

Reputation: 3386

Here:

static String[] names = new String[3];

You are initializing an array with a capacity of three items, not a maximum index of 3. To get an array with 0, 1, 2, and 3, that's four items, so you'll need to initialize the array like so:

static String[] names = new String[4]; // (0-3)

Also, loops and arrays are zero-based, so you'll want to start with a current of 0 rather than 1 to loop over your array.
Additionally and finally, you'll want to switch the <= to < in your while loop, since we want it to only go up to 3.

Upvotes: 2

burglarhobbit
burglarhobbit

Reputation: 2291

Your while loop needs fixing: When your current is equal to max, it will still check for name[4] which doesnot exist.

In Addition, == is not the best way to compare 2 Strings. You must use .equals() method as it compares value of 2 String instead of comparing 2 Object reference. This is how your while loop should be fixed:

while (found == false && current< max){

    if (names[current].equals(pName)){
        found = true;
    } else {
        current = current + 1;
    }
}

Upvotes: 2

user4668606
user4668606

Reputation:

The problem lies within this condition: found == false && current<= max - Sidenote: found == false can be simplified to !false and will still evaluate to the same result. current<=max allows the loop to run with current == max and max is defined as 4. Thus you get a read at names[4] which is out-of-bounds. The simplest solution would be to change the condition from current <= max to current<max. And current is initialized as 1. Since arrays are 0-based in java this will cause the program to ommit the first name, which is at names[0].

And another sidenote: using a constant as max is an extremely bug-prone method. Initialize max with names.length instead.

Upvotes: 2

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