Need help of my java code

Question

I wrote a java program "Test" which is:

class Get{
    static void fIntarray(int[] b){
        b = {10};
    }
}

class Test{
    public static void main(String[] args){
        int[] a;
        Get.fIntarray(a);
        System.out.println(a[0]);
    }
}

But when I compiled it, the compiler reported following faults:

Test.java:3: error: illegal start of expression
        b = {10};
Test.java:3: error:not a statement
        b = {10};
Test.java:3: error: ";" expected
        b = {10};
Test.java:5: error: class, interface, or enum expected
}

I want to create an integer array a and give value 10 to array a by passing a in the method fIntarray in Get class. I don't know where it's going wrong?

You could write `b = new int[] { 10 };` but that still wouldn't do what you want, because arguments are passed by value in Java - assigning a new value to `b` won't change `a`. — Jon Skeet, Mar 07 '18 at 07:46
It works. But why it is not the case that I assign the pointer of a to fIntarray and in the method it changes where a points? — Victoria, Mar 07 '18 at 07:54
@Victoria Read this: [Is Java “pass-by-reference” or “pass-by-value”?](https://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value) — Erwin Bolwidt, Mar 07 '18 at 07:56
@Victoria [Is Java “pass-by-reference” or “pass-by-value”?](https://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value) — BackSlash, Mar 07 '18 at 07:56
Even if you fix "b" initialization, this code won't compile because of "int[] a" line - it causes "Variable a might not be initialized" exception. About following runtime exceptions see comments above. — amseager, Mar 07 '18 at 08:00

Przemysław Moskal · Answer 1 · 2018-03-07T08:26:32.147

1

class Get{
    static int[] fIntarray(){ // you don't need to pass an array as argument here
        return new int[] {10};
    }
}

class Test{
    public static void main(String[] args){
        int[] a;
        a = Get.fIntarray(); // here you assign return value of Get.fIntarray() method to "a" array
        System.out.println(a[0]);
    }
}

You might want to see this question (as suggested in comments section) to understand why changes that you try to make to an array, doesn't take effect.

edited Mar 07 '18 at 08:26

answered Mar 07 '18 at 08:02

Przemysław Moskal

3,551
2
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I have written the same code like this. I want to also write a method with parameters but I haven't figured out yet. – Victoria Mar 07 '18 at 08:05
@Victoria When I was preparing my answer, I haven't been looking for answers of others. Anyway, I see some differences in our solutions. – Przemysław Moskal Mar 07 '18 at 08:08
I mean that I've written code in this way and I want to use another method in which the parameters are included in the method – Victoria Mar 07 '18 at 08:10
You don't even need to initialize the array with null. – Mar 07 '18 at 08:11
@Victoria Parameter is not needed here. `fIntarray()` is here just to provide/return an array containg one element. You just need to assign this return value to an array. If you would create`fIntarray()` in the same class as array that you want to assign this return value to, it would make more sense to pass this array as argument. – Przemysław Moskal Mar 07 '18 at 08:16

score 0 · Answer 2 · answered Mar 07 '18 at 08:00

0

is this solution okey for you ?

class Get{
static int[] fIntarray(int[] b){
    b = new int[]{10};
    return b;
}
}

class Test{
public static void main(String[] args){
    int[] a = null;
    a=Get.fIntarray(a);
    System.out.println(a[0]);
}
}

answered Mar 07 '18 at 08:00

Elarbi Mohamed Aymen

1,617
2
14
26

2

It works but produces warnings. You don't need to pass any parameters to fIntarray method in this case. – amseager Mar 07 '18 at 08:02

score 0 · Answer 3 · answered Mar 07 '18 at 09:34

Java is pass-by-value, so if you reassign the array b inside your method, it would not change the passed array a outside.

Example:

class Get{
    static void fIntarray(int[] b){
        b = new int[]{10}; // This will NOT be reflected on 'a'
    }
}

class Test{
    public static void main(String[] args){
        int[] a = null; // 'a' needs to be initialized somehow, or else you get a compiler error.
        Get.fIntarray(a);
        System.out.println(a[0]); // Gives NullPointerException because 'a' was not affected by the method and is still null
    }
}

If you want your array to be filled inside your method, you need to instantiate it completely before passing it to that method.

class Get{
    static void fIntarray(int[] b){
        // Could potentially produce an ArrayIndexOutOfBoundsException if the array has length 0.
        b[0] = 10; 
    }
}

class Test{
    public static void main(String[] args){
        int[] a = new int[1]; // Create an empty array with length 1.
        Get.fIntarray(a);
        System.out.println(a[0]); // Prints 10
    }
}

score -1 · Answer 4 · answered Mar 07 '18 at 08:35

Your error is on your array initialization, in java we initialize an array using constructor like that :

int[] tab = new int[]{10,-2,12};

And this the correct code for your case :

class Get{ static void fIntarray(int[] b){ b = new int[]{10};}} Hope that it gonna be helpful, good luck.

Need help of my java code

4 Answers4