[FIXED] Java Infinite Loop with post increment op

Issue

I started learning java and came across this following code, and I was expecting it to print the numbers 1 - 9, however; it's going in an infinite loop. I was wondering why that is happening.

while (i<10) {
    System.out.println(i);
    i = i++; 
}

However, when I do this, it prints just fine:

while (i<10) {

    System.out.println(i++);
}

Solution

The statement i++ increments i by 1, returning the previous value.

This means that in the first loop, you are infinitely increasing i by 1 and then setting it back to its previous value, meaning it never changes.

However, in the second loop, you are not setting i back to its previous value, allowing it to increase and the loop to end.

To fix the first loop, change the third line from:

i = i++;

to:

i++;

Identical behaviour can also be achieved through a for loop:

for (int i = 0; i < 10; i++) {
    System.out.println(i);
}

The first statement inside the brackets is what should be run first, in this case defining i as a int with a value of 0. The next statement is the conditional that is checked before each iteration. In this example, it checks if i is less than 10. The third and final statement is the code to run at the end of each iteration. In this example, i++ is run, increase the value of i by 1 each iteration.

Answered By - KingsMMA
Answer Checked By - Timothy Miller (JavaFixing Admin)