Increasing Array's values in Java

Question

Why this code doesn't add "1" to array's values? (I have written it by "Enhanced For Loop"; when I wrote it with "old For", it worked.

public class EnhanceForLoop {
    public static void main(String[] args) {

            int[] list = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

            System.out.println("List before call addOne");
            printList(list);

            System.out.println("Calling addOne");
            addOne(list);

            System.out.println("List after call addOne");
            printList(list);
    }               

    public static void addOne(int[] list) {
        for (int val : list) {
            val = val + 1;
        }
    }

    public static void printList(int[] list) {
        System.out.println("index, value");
        for (int i = 0; i < list.length; i++) {
            System.out.println(i + ", " + list[i]);
        }
    }
}

From the for-each doc: "Therefore, the for-each loop is not usable for filtering. Similarly it is not usable for loops where you need to replace elements in a list or array as you traverse it." In short, use the for-each when you perform a read-only operation. — Alexis C.
– Alexis C., Commented Mar 27, 2015 at 9:37

deogratias · Accepted Answer · 2015-03-27 09:35:48Z

1

You are not increasing array values.Do

public static void addOne(int[] list){
     for(int i=0;i<list.length;i++){
                list[i] = list[i] + 1;
         }
}

Below statement

val = val + 1;   //will not increase array value it will increase val value

answered Mar 27, 2015 at 9:35

deogratias

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8 Comments

Viswanath Donthi Over a year ago

user is trying by pass by value, not by reference. So, it wont increment. Just check it

Shirin Over a year ago

Thank you. So, we cannot use "Enhanced For Loop" for increasing values of array, right?

Tom Over a year ago

@ViswanathD "Just check it" Yes, you should do that.

Viswanath Donthi Over a year ago

@Shirin we can use any iterating process, but the incrementation should be done on original field (list) not on passed by value.

deogratias Over a year ago

@Shirin yes in your case val does not denote array reference

|

vijay · Accepted Answer · 2015-03-27 09:37:16Z

1

The value you are increasing is for the declared variable val, which is disconnected copy of array's currently iterating index variable.

answered Mar 27, 2015 at 9:37

vijay

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