Short Circuit Expressions in C/C++ and Java

It was quite embarassing for me today. For more than 10 years since I started learning C language, I have not even heard of "short-circuit evaluation" until today. Today, I was studying a simple BinaryTree program in Java, and I encountered somewhat peculiar problem; I actually thought I found some sort of Java's fundamenetal error, but oh well. I was the culprit.

If you see a code below, what would you guess the output is?

	public class ShortCircuit {
	private static boolean funcReturningTrue () {
	System.out.println ("this function returns true");
	return true;
	}
	private static boolean funcReturningFalse () {
	System.out.println ("this function returns false");
	return false;
	}
	public static void main (String[] args) {
	if (funcReturningTrue() || funcReturningFalse())
	System.out.println ("eval 1 complete");
	if (funcReturningFalse() && funcReturningTrue())
	;
	else
	System.out.println ("eval 2 complete");
	boolean bool = (true) ? funcReturningTrue() : funcReturningFalse();
	System.out.println ("bool = " + bool);
	}
	}

view raw ShortCircuit.java hosted with ❤ by GitHub

public class ShortCircuit {
    private static boolean funcReturningTrue () {
        System.out.println ("this function returns true");
        return true;
    }
    private static boolean funcReturningFalse () {
        System.out.println ("this function returns false");
        return false;
    }
    
    public static void main (String[] args) {
        if (funcReturningTrue() || funcReturningFalse())
            System.out.println ("eval 1 complete");
            
        if (funcReturningFalse() && funcReturningTrue())
            ;
        else
            System.out.println ("eval 2 complete");
            
        boolean bool = (true) ? funcReturningTrue() : funcReturningFalse();
        System.out.println ("bool = " + bool);
    }
}

Well, I naively thought that both static methods inside if () evaluation would be called; I was wrong. It seems that there are some short-circuit implementation in order to save run time. For example, (true || bool) is evaluated to be true regardless of bool, so C/C++ and Java will not even evaluate bool. That is, only funcReturningTrue() will be called in the code above for the 1st if statement.

Similarly, (false && bool) is false regardless of bool, so again bool will not be evaluated. This corresponds to the 2nd if statement in the code above.

Lastly, the statement (condition) ? a : b will evaluate only a or b but not both depending on the condition. If one were to make sure that both conditions to be evaluated in the examples above, one should use | and & in place of || and &&.

Now, one can easily predict the output of the program above:
this function returns true
eval 1 complete
this function returns false
eval 2 complete
this function returns true
bool = true