Why does j = j assign 0 to j in Java?

Post Increment Operator in Java

Question:

In the code snippet below, why does the post increment operator j assign 0 to j?

public class Test {
    public static void main(String[] args) {
        int j = 0;
        for (int i = 0; i < 100; i++) {
            j = j++;
        }
        System.out.println(j); // prints 0
    }
}

According to the author of the book "Java Puzzlers," the statement j = j is similar to the following sequence:

temp = j;
j = j + 1;
j = temp;

However, the statement a = b assigns b the value 1, which contradicts the expected behavior of the post increment operator.

Answer:

The mistake in the argument lies in applying the rule of increment then assign to a = b but not to j = j . The correct sequence of operations for a = b is:

temp = b;
b = b + 1; // increment
a = temp; // assign

Applying the same rule to j = j , we get:

j = j;
j = j + 1; // increment

As the initial value of j was 0, the post increment operator returns 0 because the value of j before the increment is used in the expression.

Therefore, the final value of j is 0 because the assignment statement evaluates to j = 0.

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