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I have a for loop, and I initialise the variables inside that loop. After it, I need to manipulate that variables, but the compiler says that variables are not initialised. 

public class Solution {
    static void displayPathtoPrincess(int n, String[] grid) {
        String[][] visual = new String[n][n];
        for (int i = 0; i < n; i++) {
            char[] myGrid = grid[i].toCharArray();
            for (int j = 0; j < n; j++) {
                visual[i][j] = myGrid[j] + "";
            }
        }

        int pX;
        int pY;
        int bX;
        int bY;
        // rescue the princess
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                if (visual[i][j].equals("p")) {
                    pX = j;
                    pY = i;
                }
                if (visual[i][j].equals("m")) {
                    bX = j;
                    bY = i;
                }
            }
        }
        System.out.println(pY + "");
        System.out.println(pX + "");
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int m;
        m = in.nextInt();
        String grid[] = new String[m];
        for (int i = 0; i < m; i++) {
            grid[i] = in.next();
        }

        displayPathtoPrincess(m, grid);
    }
}

if condition is true at some point. In fact if I move the print statements inside the if it works.
How can solve this problem?

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2
  • Are you sure that the first if statement condition is true at some point in your loop? If it isn't, pX and pY won't get values. Commented Oct 3, 2015 at 14:31
  • totally sure. If I print the value inside the loop it works. Commented Oct 3, 2015 at 14:33

4 Answers 4

Reset to default
1

If you want to initialize your variables in conditions, then you need to set them to a default value :

int pX = 0;
int pY = 0;
int bX = 0;
int bY = 0;

That way, your compiler will not return the initialization issue any more.

EDIT

I made some modifications, since I could not make your code work (cast from string to int, array of char initialization issue, etc.). Could you try this please :

public class Solution {
static void displayPathtoPrincess(String grid) {
    int n = grid.length();
    String[][] visual = new String[n][n];
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            visual[i][j] = String.valueOf(grid.charAt(j));
        }
    }

    int pX = 0;
    int pY = 0;
    int bX;
    int bY;
    // rescue the princess
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            if (visual[i][j].equals("p")) {
                pX = j;
                pY = i;
            }
            if (visual[i][j].equals("m")) {
                bX = j;
                bY = i;
            }
        }
    }
    System.out.println(pY + "");
    System.out.println(pX + "");
}

public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    String grid = in.next();

    displayPathtoPrincess(grid);
}

It probably isn't what you want to do, but I have no problem with your variables' values initialized in conditions.

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10 Comments

I tried it. If I do so, then the value of the variable after the loop is 0.
can you show us the way your visual[i][j] is set to its value ? Your condition is just returning false, and your variables are keeping their default values.
As I said, at some point the if is true. And I can print the value inside the If.
Show me the code please. How are visual[i][j] and n initialized ?
I am having some issues with your "myGrid" variable in displayPathToPrincess method. I think this array's initialization is wrong. Could you give me the values you are giving to your scanner please ? The if conditions are always wrong for me...
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Below excerpt from JLS §16 (Definite Assignment)

For every access of a local variable or blank final field x, x must be definitely assigned before the access, or a compile-time error occurs.

If you using a local variable at any point in your method, and compiler is not sure that local variable would be initialized when actually running the program then compiler will show error that please initialize local variable.

In you case, if n is 0 then your for (int i = 0; i < n; i++) { loop will never run, so compiler cannot be sure that at this point System.out.println(pY + "");, pY would be in initialized state, so complains.

For solution: You must initialize local variable before using/reading it.

You are able to print pX and pY because compiler is sure at this point that values would be initialized, however try below and even in your IF block you will see that there is compilation error because you would be trying to read the local variables before they were initialized, so compiler complains.

So, bottom line - make compiler believe that local variable would have been initialized at that point, so initialize local variables before using them.

if (visual[i][j].equals("p")) {
                    System.out.println(pY + "");  //Compilation error because compiler is not sure if LV would be in initialized state.
                    pX = j;
                    pY = i;
                    System.out.println(pY + "");  //Happy compiler becuse it is sure that LV are just initialized.
                }
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8 Comments

It's ok, but if I initialise them with 0, then their value will be 0 even after the loop.
Even if you don't initialize them then there would be garbage value, right? You are getting problem because you are trying to print the pX and pY using System.out.println(pX + "");, if you don't print them then you will be able to compiler. So, it makes sense to read value when there would actually be some value. In the end of FOR loop, if there is no value then there is no point of printing. If for debugging you want to see if pX and pY were initialized then use a boolean to do a check (initially FALSE, make true in IF and then read in end.).
I need to do some manipulation. I cannot access them outside of the loop? How could I tackle this?
If for debugging purpose (I am not recommending, I hv told that initialize LV) you want to read the values in the end, then there would be 2 approaches - (1.) Use a boolean to do a check (initially FALSE, make true in IF and then read in end.) (2.) Use another set of LV, initialize them to 0, then set is same as pX and pY, and then read them in end. If you are using some IDE then you really don't need this, you can debug.
No, those LV's CANNOT be accessed outside FOR loop if you don't initialize them. If purpose is debugging then I have given you to approaches above. What manipulation you want to do.
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you could try this

class Demo
{
static int pX;
static int pY;
static int bX;
static int bY;

public static void main(String a)
{
for (int i = 0; i < n; i++) {
    for(int j = 0; j < n; j++) {
        if (visual[i][j].equals("p")) {
            pX = j;
            pY = i;
        }
        if (visual[i][j].equals("m")) {
            bX = j;
            bY = i;
        }
    }
}
System.out.println(pY + "");
System.out.println(pX + ""); 
}

}
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2 Comments

this might work, but the static ints seem wholly inappropriate for what appears to be temporary data. better to just initialize the int values to 0
Scope rules are violated here. If the variables are only used inside the block, they should be scoped inside the block.
0

The compiler needs to see that the variables have been definitely assigned regardless of which path through the loop the execution actually takes at runtime.

It doesn't know if either of the if branches will run when your program executes.

It is a good practice to always give your variables an initial value to avoid these kind of issues.

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1 Comment

It's ok, but if I initialise them with 0, then their value will be 0 even after the loop.

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