Java array pass without reference

Question

I am trying to pass an array without using a reference, but directly with the values :

    public static void main(String[] args){
            int[] result = insertionSort({10,3,4,12,2});
    }

    public static int[] insertionSort(int[] arr){
        return arr;
    }

but it returns the following exception :

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
Syntax error on token(s), misplaced construct(s)
Syntax error on token ")", delete this token

When I try the following code , it works , can anybody please explain the reason ?

    public static void main(String[] args){
        int[] arr = {10,3,4,12,2};
        int[] result = insertionSort(arr);  
    }

    public static int[] insertionSort(int[] arr){
        return arr;
    }

An important note: Java never passes by reference, only by value. — Luiggi Mendoza
– Luiggi Mendoza, Commented Sep 30, 2012 at 18:16
What do you mean exactly by value not by reference ? because when I pass an array to a method which manipulates values of this array , values of the original array change too . Therefor , sometime I need to clone an array if I don't want the original array to be changed ! — Arian
– Arian, Commented Sep 30, 2012 at 19:57
Try to receive an array in a method and initialize the array inside the method (new int[20] or similar will do), then pass a null array to the method and print the array outside the method, it will still be null, that's because Java passes by value, not the reference of the object. — Luiggi Mendoza
– Luiggi Mendoza, Commented Sep 30, 2012 at 20:08

Bhesh Gurung · Accepted Answer · 2012-09-30 18:14:54Z

10

It has to be

int[] result = insertionSort(new int[]{10,3,4,12,2});

{10,3,4,12,2} is a syntactic sugar for array initialization, which must go with the declaration statement like the one in the following -

int[] arr = {10,3,4,12,2};

Something as follows is not allowed too -

int[] arr; // already declared here but not initialized yet
arr = {10,3,4,12,2}; // not a declaration statement so not allowed

edited Sep 30, 2012 at 18:14

answered Sep 30, 2012 at 18:08

Bhesh Gurung

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Comments

Bhesh Gurung · Accepted Answer · 2012-09-30 18:22:12Z

5

insertionSort({10,3,4,12,2})

is not valid java because you don't specify a type in your method call. The JVM does not know what type of array this is. Is it an array with double values or with int values?

What you can do is insertionSort(new int[]{10, 3 ,4 12, 2});

edited Sep 30, 2012 at 18:22

Bhesh Gurung

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answered Sep 30, 2012 at 18:11

Jan Koester

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moonwave99 · Accepted Answer · 2012-09-30 18:10:06Z

1

int[] array = { a, b, ...., n } is a shorthand initialization - you have to write:

int[] result = insertionSort(new int[]{10,3,4,12,2});

to initialize it anonymously.

answered Sep 30, 2012 at 18:10

moonwave99

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gd1 · Accepted Answer · 2012-09-30 18:13:43Z

1

Nothing much to add to what others said.

However I believe the reason why you should use new int[]{10,3,4,12,2} (like others stated) and Java doesn't let you use just {10,3,4,12,2} is that Java is strong typed.

If you just use {10,3,4,12,2} there is no clue of what the type of the array elements can be. They seem to be integers, but they can be int, long, float, double, etc...

Well, actually it might infer the type from the method signature, and fire a compile error if it doesn't fit, but it seems complicated.

answered Sep 30, 2012 at 18:13

gd1

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1 Comment

moonwave99 Over a year ago

+1 for pointing out that Java would have no clue on guessing the elements type.

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