Why is the output of this code 111111?

Question

This is the code. I tried to solve it, but I can\'t understand how its output is 111111?

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


        

Answer 1

Hi I will try to explain what is happening in this code snippet

public class Test { 
  public static void main(String[] args) {
    int list[] = {1, 2, 3, 4, 5, 6};

This line is the equivalent of the following code

    int list[] = new int[6];
    list[0] = 1;
    list[1] = 2;
    list[2] = 3;
    list[3] = 4;
    list[4] = 5;
    list[5] = 6;


    for (int i = 1; i < list.length; i++)
      list[i] = list[i - 1];

this loop is the equivalent of the following code

    list[1] = list[0];
    list[2] = list[1];
    list[3] = list[2];
    list[4] = list[3];
    list[5] = list[4];

which because list[0] = 1 is the equivalent of the following

    list[1] = 1;
    list[2] = 1;
    list[3] = 1;
    list[4] = 1;
    list[5] = 1;


    for (int i = 0; i < list.length; i++)
      System.out.print(list[i] + " ");
  }
}

Which is why you are getting the output you are getting

Answer 2

The output is 1 1 1 1 1 1 because the first for statement is looping over an array, named list, of values (i.e. {1, 2, 3, 4, 5, 6}) and replacing each one with the previous one, starting at the 2nd one (index 1; or, as some may say, the 1st one where the "real" first one is the 0th one … I digress). Thus the 2nd (index 1) item's current value (2) gets replaced by the 1st (index 0) item's value, which is 1: (list[i] = list[i - 1]; where i = 1). This continues down the array of integers until we reach the end of list. As we replace each value with the one before it, they all eventually just become the same value – that of the first item in the array, which is 1. In the end we have this value for our list: {1, 1, 1, 1, 1, 1}.

The next for statement simply prints out each value of the updated list in turn followed by a blank space: System.out.print(list[i] + " ");. So, as you can see, the result of running this code is that it prints out 1 1 1 1 1 1.

Just to drive the point home in a more visual way, let's just map out the values of the list array over time:

int i = 1;              // i = 1
list[i] = list[i - 1];  // list[1] = list[1 - 1]; list[0] == 1
                        // list is now {1, 1, 3, 4, 5, 6}

i++;                    // i = i + 1 # i is now 2
list[i] = list[i - 1];  // list[2] = list[2 - 1]; list[1] == 1
                        // list is now {1, 1, 1, 4, 5, 6}

i++;                    // i = i + 1; i = 3
list[i] = list[i - 1];  // list[3] = list[3 - 1]; list[2] == 1
                        // list is now {1, 1, 1, 1, 5, 6}

i++;                    // i = i + 1; i = 4
list[i] = list[i - 1];  // list[4] = list[4 - 1]; list[3] == 1
                        // list is now {1, 1, 1, 1, 1, 6}

i++;                    // i = i + 1; i = 5
list[i] = list[i - 1];  // list[5] = list[5 - 1]; list[4] == 1
                        // list is now {1, 1, 1, 1, 1, 1}

i++;                    // i = i + 1; i = 6
i < list.length;        // i == 6; list.length == 6; 6 < 6 == false
                        // exit the for loop

I sure hope that helps you understand the concepts at play here a little better. Good luck on the rest of your test!

Answer 3

for (int i = 1; i < list.length; i++)
      list[i] = list[i - 1];

is equivalent to:

list[1] = list[1-1] = list[0] = 1
list[2] = list[2-1] = list[1] = 1
list[3] = list[3-1] = list[2] = 1
list[4] = list[4-1] = list[3] = 1
list[5] = list[5-1] = list[4] = 1

Got it?