Comparison operators

A condition is usually a comparison. Java has six comparison operators, and each one gives true or false:

== compares, = assigns

Comparing uses two equals signs. With one, Java reads it as an assignment. An assignment has a value too, the value it stores: here that's the int 5, and an if needs true or false:

public class Main {
    public static void main(String[] args) {
        int number = 5;
        if (number = 5) {
            System.out.println("Five!");
        }
    }
}

Main.java:4: error: incompatible types: int cannot be converted to boolean
        if (number = 5) {
                   ^
1 error

With numbers the compiler catches this mistake. With a boolean variable (the next module introduces them) it can't: if (done = true) stores true in done, compiles without a warning, and the block always runs. To compare, always use ==.

These operators compare numbers. Comparing text is different, and the next module shows how.