Doubt regarding "null" in java

[Mansukhdeep Thind]

Hi

Please have a look at the following code snippet:

public class EmptyStringsTest {
    public static boolean isEmpty(String s) {
        return (s == null | s.length() == 0);
    }

    public static void main(String args[]) {
        if (isEmpty(null)) {
            System.out.print("empty ");
        } else {
            System.out.print("not_empty ");
        }
    }
}

When we invoke the method isEmpty with null as argument, why does it not return boolean value "true" for s==null. Isn't null==null true?

[Seetharaman Venkatasamy]

Mansukhdeep Thind wrote:Isn't null==null true?

Let's test : System.out.println(null == null);

If you get exception in runtime. you have to analyze why you are getting that

[Mansukhdeep Thind]

I followed your instruction. printing null==null does in fact return a Boolean true. Then why does

s == null

throw null pointer exception? Or is it simply the act of passing a null to the method that spoils the show?

[Mansukhdeep Thind]

I just realized I am thinking on wrong lines. It is the bitwise OR operator that is causing harm. How does this "|" operator function. What s meant by bitwise OR?

[Henry Wong]

Mansukhdeep Thind wrote:I just realized I am thinking on wrong lines. It is the bitwise OR operator that is causing harm. How does this "|" operator function. What s meant by bitwise OR?

As you figured out, a bitwise OR doesn't short circuit. It is used to OR all the bits of the two operands. From your code, the logical OR is what you need.

Henry

[Mansukhdeep Thind]

So when the JVM tries to evaluate s.length, it hits a brick wall as String reference "s" is null(pointing to nothing). Hence, the stack explodes throwing a NullPointerException. Correct Henry?