Why in Java, (“string”).equals(var) recommended other than (var).equals(“string”)?

Question

I have seen most cases developers use first string and after that variable used in .equal operation. What is the reason?

Answer 1

I would not use ("string").equals(var), since it may show that the programmer does not know if var might be null or not. I would document if a var can be null or not and check it.

Example:

String makeAString(@NonNull String aStringValue) {
    Validate.notNull(aStringValue, "aStringValue must not be null");
    if (aStringValue.equals("abcde") {
       return "fg";
   } else {
       return "de";
   }
}

String makeAString(@Nullable String aStringValue) {
    if (aStringValue == null) {
       return "kl";
    }
    if (aStringValue.equals("abcde") {
       return "fg";
    } else {
       return "de";
    }
}