Precedence in Java

Question

Unary postfix increment and decrement operators have more preceedence than relational operators according to precedence table, so why in a expression like this (x++ >=10) the relational operator evaluated first and then the variable is incremented?

Answer 1

The operator isn't evaluated first. The ordering is:

• Evaluate LHS (x++) - the result is the original value of x, then x is incremented
• Evaluate RHS (10) - the result is 10
• Compare the results of the LHS and RHS

Here's code to demonstrate that:

public class Test {

    static int x = 9;

    public static void main(String[] args) {
        boolean result = x++ >= showXAndReturn10();
        System.out.println(result); // False
    }

    private static int showXAndReturn10() {
        System.out.println(x); // 10
        return 10;
    }
}

That prints out 10 then false, because by the time the RHS is evaluated x has been incremented... but the >= operator is still evaluating 9 >= 10 as the result of the expression x++ is the original value of x, not the incremented one.

If you want the result after incrementing, use ++x instead.