CODEWITHSUNDEEP
java
Jack
Jack

Reputation: 15

Why does this program print out "4 2 1 0"?

Can someone explain the output of this code? I'm very confused. Before I compiled this code, I thought the output was "4 1 2 3". After compiling the code, it is "4 2 1 0". I'm not sure why so i'm wondering if someone can explain it to me?

public class activity1
{
public static void main(String[]args)
{
//Declare and initialize array
int []list1 = {3,2,1,4};            
int [] list2 = {1,2,3};
list2= list1;
list1[0]=0;
list1[1]=1;
list2[2]=2;
//Create for loop   
for (int i = list2.length-1; i>=0;i--)
{
System.out.print(list2[i] + " ");//print out the array
}
}
}

Upvotes: 0

Views: 71

Answers (3)

user2173372
user2173372

Reputation: 513

You can debug and see for yourself what the code is doing at every line:

public static void main(String[] args) {
    // Declare and initialize array
    int[] list1 = {3, 2, 1, 4};
    int[] list2 = {1, 2, 3};
    list2 = list1; // list1 = [3, 2, 1, 4] list2 = [3, 2, 1, 4]
    list1[0] = 0; // list1 = [0, 2, 1, 4] list2 = [0, 2, 1, 4]
    list1[1] = 1; // list1 = [0, 1, 1, 4] list2 = [0, 1, 1, 4]
    list2[2] = 2; // list1 = [0, 1, 2, 4] list2 = [0, 1, 2, 4]

    // Create for loop
    // You are printing list2 in reverse order
    for (int i = list2.length - 1; i >= 0; i--) {
      System.out.print(list2[i] + " ");// print out the array
    }
}

Upvotes: 1

Steve Pallen
Steve Pallen

Reputation: 4507

The assignment is just moving a reference to list1 into the list2 variable. So, both variables reference the same array. If you want to copy the array, you will need copy each item from list1 to list 2.

Upvotes: 0

Elliott Frisch
Elliott Frisch

Reputation: 201447

After list2= list1; there is only one array. {3, 2, 1, 4}

Then, it's modified to {0, 1, 2, 4} and then it's printed backwards.

Upvotes: 2

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