Ternary Operator - JAVA

Question

Is it possible to change this:

if(String!= null) {

    callFunction(parameters);

} else {

    // Intentionally left blank

}

...to a ternary operator?

Solution 1

Well, the ternary operator in Java acts like this...

return_value = (true-false condition) ? (if true expression) : (if false expression);

...Another way of looking at it...

return_value = (true-false condition) 
             ? (if true expression) 
             : (if false expression);

---

You question is kind of vague and we have to assume here.

• If (and only if) callFunction(...) declares a non-void return value (Object, String, int, double, etc..) - it seems like it does not do that via your code - then you could do this...

  return_value = (string != null) 
               ? (callFunction(...)) 
               : (null);
  

• If callFunction(...) does not return a value, then you cannot use the ternary operator! Simple as that. You will be using something that you don't need.

  • Please post more code to clear up any issues

---

Nonetheless, ternary operator should represent alternative assignments only!! Your code does not seem to do that, so you should not be doing that.

This is how they should work...

if (obj != null) {            // If-else statement

    retVal = obj.getValue();  // One alternative assignment for retVal

} else {

    retVal = "";              // Second alternative assignment for retVale

}

This can be converted to...

retVal = (obj != null)
       ? (obj.getValue())
       : ("");

---

Since it seems like you might be trying to just refactor this code to be a one-liner, I have added the following

Also, if your false-clause is truely empty, then you can do this...

if (string != null) {

    callFunction(...);

} // Take note that there is not false clause because it isn't needed

OR

if (string != null) callFunction(...);  // One-liner

Solution 2

Yes. You can with keeping same null in else block.

String result = str !=null ?  callFunction(parameters) : null;

Make sure that callFunction(parameters) return a String.

Solution 3

The ternary operator can be used to combine two expressions but an empty statement is not an expression.

A method invocation can be used as an expression if the method returns a value (read: is not declared void) and it could be used together with a dummy constant null to form a ternary operator but the result would be again an expression which is not allowed in places where a statement is required, in other words, it can not replace an if statement.

By adding another construct taking an expression and imposing no additional side effect you can construct a complete replacement. E.g. by declaring and assigning a new, otherwise unused, local variable you get:

Object dummy=condition? callFunction(parameters): null;

But there is no benefit over simply saying if(condition) callFunction(parameters);. It might even add unnecessary overhead as it will perform auto-boxing if the return value is a primitive type.

With Java 8 there is a solution to the puzzle that works even for void methods:

((Runnable)(condition? ()->callFunction(parameters): ()->{})).run();

but it still has no advantage over simply using if.

Solution 4

It could be possible if your method callFunction() has a return type. Then, you could do it like SURESH ATTA wrote in his answer:

String result = str!=null ? callFunction(str) : null;

Or with any other type for result or any other arguments. If you want to call a method in the else-Statement too, this one needs to have the same return type as the one in your if-statement.

If your method doesn't have a return type / the return type of callFunction() is void, it is not possible to change your if-else-statement into a ternary operator.

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