Here's a simple way to test it:
public class OperatorTest {
public static void main(String[] args) {
boolean a = false;
a &= b();
}
private static boolean b() {
System.out.println("b() was called");
return true;
}
}
The output is b() was called, therefore the right-hand operand is evaluated.
So, as already mentioned by others, a &= b is the same as a = a & b.