using null as arguments

[nick Mercado]

I have a question is using null as argument to pass to the parameter a good (or okay) java convention?

I have a boolean method that takes 2 string parameters and inside the method I pass 2 string objects as argument and 1 non-existing String value (null)

Something like this.

  boolean checkTwoStrings(String a, String b) {
    return checkStrings(a, b, null);
  }
  
  boolean checkThreeStrings(String a, String b, String c) {
    return checkParam(a, b, c);
  }
  
  boolean checkParam(String a, String b, String c) {
    // check if a and b is same 
    if (c == null) {
      if (a.equals(b)) {
        return true;
      }
    }
    
    // check if c is same as a or b
    if (c.equals(a) || c.equals(b)) {
      return true;
    }
    return false;
  }

Is it okay to use null as argument?

[nick Mercado]

Sorry for typo, line 2 should be

    return checkParam(a, b, null);

[Knute Snortum]

Hi nick,

I don't see anything wrong with what you did in this situation.  In other situations you have to be careful to avoid a NullPointerException, but if the method is expecting null as a possible argument, then it's fine.

[Fred Kleinschmidt]

Note also that before you use variables a or b, you should also check them to ensure they are not null, to avoid getting a NullPointerException.

[Piet Souris]

What is the intention of the checks?

As it is now, the result of the method "checkParam" may depend on the particular order of the three parameters. Try, for instance, this:

System.out.println("a, a, b: " + checkParam("a", "a", "b"));
System.out.println("a, b, a: " + checkParam("a", "b", "a"));
System.out.println("a, b, null: " + checkParam("a", "b", null));

Why do you get a NullPointerException in the third case?

And, as Fred says, check the parmeters a and b for a possible null value.

[Piet Souris]

As an alternative to having separate methods for the two and the three parameter cases, you could use a method with a veriable number of Strings as parameter.
For instnce:

checkParameters(String... strings) {...}

But whether that is useful depends on what exactly you are trying to achieve.

[Junilu Lacar]

Your checkParam method will throw a NullPointerException when c is null and a is not equal to b.

Avoid writing this:

if (conditional_expression) {
    return true;
} else {
    return false;
}

That's equivalent to what you wrote on lines 18-21.  You can simplify that to

return (conditional_expression)