Calling equals on string literal

Question

I just was tidying my code a bit and there was this piece:

String saving = getValue();
if(saving != null && saving.equals(\"true\")){
   // do someth         


        

Answer 1

The format of putting the literal first avoids the potential NPE and will always be false for "literal".equals(null).

This is because a "literal" expression always evaluates to a String object (and is thus never null) and String.equals(obj) checks to see if the other object is a null (via asinstanceof). An object is an object - no need to worry bout the "heap".

It's good practice to have a null-guard in an equals implementation as null.equals(null) is not permissible: "The equals method implements an equivalence relation on non-null object references"

Here is the String.equals the source (for OpenJDK):

public boolean equals(Object anObject) {
    if (this == anObject) {
        return true;
    }
    if (anObject instanceof String) {
        // ..
    }
    return false;
}