Error in my simple java code..!

Question

public class Test {
    public static void main(String... args) {

        int[][] arrayOfInts = {
            {23, 3, 65, 46},
            {65, 55, 2, 3},
            {55, 22, 35, 47}
        };
        int i, j, toFind = 2;

        boolean foundIt = false;

        search:
        for(i = 0; i < arrayOfInts.length; i++) {
            for(j = 0; j < arrayOfInts[i].length; j++) {
                if(arrayOfInts[i][j] == toFind) {
                    foundIt = true;
                    break search;
                }
            }
        }

        if(foundIt) 
            System.out.println("Element found at index " + i + ", " + j);
        else
            System.out.println("Element not found");
    }
}

Dear SO, I'm having trouble compiling the above code. My code works perfect when i initialize my integer variable j to 0 (j = 0).

But my question is Why should i initialize j = 0 ? Why am I getting variable j might not have been initialized error in the line

System.out.println("Element found at index " + i + ", "+ J);

If my int variable i is storing a value why cant j store.. ??

P.S. Noob here..!!

To expand on the other answers, arrayOfInts.length is calculated at runtime, not at compile time. In this very simple case a compiler could probably determine that arrayOfInts.length could not possibly be zero (we can see it's not zero just by reading the code) but in the more general case it cannot. Hence the compiler assumes that the inner for loop may never be executed. — jarmod
– jarmod, Commented May 31, 2013 at 11:20

TecHunter · Accepted Answer · 2013-05-31 11:16:53Z

2

Because imagine if you have arrayOfInts.length==0?

Then you never enter the loop --> j not initialized.

To prove my point try compiling and running with

int[][] arrayOfInts = {};

answered May 31, 2013 at 11:16

TecHunter

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1 Comment

vikingsteve Over a year ago

so try int i = 0, j = 0, toFind = 2; or, even better, use 3 lines for that.

devrobf · Accepted Answer · 2013-05-31 11:17:05Z

2

The reason is that, as far as the compiler is concerned, arrayOfInts.length could be 0 at runtime. If this happened, your for loop would never run - therefore, j would never have been initialised in the inner loop.

answered May 31, 2013 at 11:17

devrobf

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Comments

Grijesh Chauhan · Accepted Answer · 2013-05-31 11:24:12Z

1

Suppose your outer for loop for(i = 0; i < arrayOfInts.length; i++) { never get chance to executes for some execution instance (as first time i < arrayOfInts.length false when length of array = 0) then j will remain uninitialized. And if foundIt be true, No value for j to print in if block hence error.

edited May 31, 2013 at 11:24

answered May 31, 2013 at 11:18

Grijesh Chauhan

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Alexandre Lavoie · Accepted Answer · 2013-05-31 11:17:04Z

1

Since arrayOfInts.length could be 0, your loop may be never executed. In that case, your variable j will never be assigned a value.

answered May 31, 2013 at 11:17

Alexandre Lavoie

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Denys Séguret · Accepted Answer · 2013-05-31 11:17:18Z

1

It needs a lot of computation to check that you really put something in j before you use it in your println statement.

K, for example, wouldn't be initialized if arrayOfInts was of size 0.

That's why you have to initialize j, to let the compiler be sure it's initialized before you use it.

answered May 31, 2013 at 11:17

Denys Séguret

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jcage · Accepted Answer · 2013-05-31 11:18:09Z

1

Because it is not a given that your inner loop, which initializes j will execute. Keep in mind that loop execution is conditional, so the conditions on your outer loop (the one with i) might not be true. In that case, the line that initializes j will never execute.

answered May 31, 2013 at 11:18

jcage

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Comments

dharam · Accepted Answer · 2013-05-31 11:28:39Z

In java every local variable needs to be initialized.

On the first line of the for loop the variable i is getting initialized to 0. But the compiler is not sure if the second for loop will even get a chance to execute. Assume that

 arrayOfInts.length is 0.

In this case the j value will not be initialized.

A nice thing would be to test it by changing the if(foundIt) to if(false), the compile will stop complaining.

EDIT Its all about, the compiler never assume things. It works on facts available and the fact there says the following: 1) i will always have a value. 2 j might not get a value and remain uninitialized. 3) foundIt can be true. :)

Moreover, its a really nice practice to initialize variables before using them.

The class level variables are automatically initialized to their default values at the class initialization time. But the method local variables are not, hence the complain/compile time error.

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