Java Nested If-else shorthand

Question

if (getNo() != null ? !compareNo(getNo(), b.getNo()) : getNo() != null) {
  return 100;
}

Assuming getNo() is not null, does this mean that return 100 runs if !compareNo(getNo(), b.getNo()) evaluates to true?

What happens to the last expression (after the :)

Regardless of the outcome, you should really consider expanding this into multiple checks or multiple lines. Less lines of code does not mean better. This piece of code means I have to read it 10 times in order to understand what it's saying. That's bad from a maintenance point of view. — SurfMan, Jan 29 '18 at 19:57
Possible duplicate of [What is the Java ?: operator called and what does it do?](https://stackoverflow.com/questions/798545/what-is-the-java-operator-called-and-what-does-it-do) — Bernhard Barker, Jan 29 '18 at 20:00
I'm trying to understand someone else's code, so i agree that it's not easy to read. — stumped, Jan 29 '18 at 20:00
@SurfMan The biggest problem here is that the "else" of the ternary is the same boolean as up front--this could be perfectly readably written as `if(get(No) != null || !compare...` — chrylis -cautiouslyoptimistic-, Jan 29 '18 at 20:03
I think I get it now, the "if" part is returning a boolean, and the "else" part is doing that too. — stumped, Jan 29 '18 at 20:04
@chrylis I think you mean `getNo() != null && !compareNo...`. You don't want the second part evaluated if the first part is false. — Bernhard Barker, Jan 29 '18 at 20:05
@chrylis - probably not. It seems to me that `getNo()` probably reads a number from some kind of stream, or other structure. So consecutive calls to `getNo()` probably don't return the same thing. I think OP needs to make sure that whatever happens, `getNo()` gets called twice. — Dawood ibn Kareem, Jan 29 '18 at 20:10
Its necessary to use `code` tag to separate it from other text — Shahriar, Jan 30 '18 at 08:37

nvioli · Accepted Answer · 2018-01-29T20:08:21.277

What a mess. Let me refactor things so I can see what's going on:

if (getNo() != null ? !compareNo(getNo(), b.getNo()) : getNo() != null) 
{
  return 100;
}

is the same as

Boolean mainCondition = getNo() != null ? !compareNo(getNo(), b.getNo()) : getNo() != null;
if (mainCondition) 
{
  return 100;
}

is the same as

Boolean mainCondition;
if (getNo() != null) {
  mainCondition = !compareNo(getNo(), b.getNo());
} else {
  mainCondition = getNo() != null;
}
if (mainCondition) 
{
  return 100;
}

but if getNo() is null, then we find ourselves in the else condition, which will set mainCondition to false, so we will not return, i.e. a simpler way to write this is:

if (getNo() != null) {
  if (!compareNo(getNo(), b.getNo())) 
  {
    return 100;
  }
}

or

if (getNo() != null && !compareNo(getNo(), b.getNo())) {
  return 100;
}

The answer is yes: if !compareNo(getNo(), b.getNo()) is true, then the original statement will return 100.

As for what happens to the part after the :, it will not be evaluated unless getNo() is null, however if getNo() is indeed null, then we already know the outcome, so it's quite redundant to include it there.

So if getNo() != null, then "!compareNo(getNo(), b.getNo())" evaluates, and if it evaluates to true, then you execute the return, and if it evaluates to false, it doesn't do anything? — stumped, Jan 29 '18 at 20:14
Pretty much! If it evaluates to false, then we would evaluate the last part of the ternary operator (after the `:`), but we already know that evaluates to false since what's there is exactly the same as the original condition. So the ternary will evaluate to false, so the `return` will not run. As you said, it doesn't do anything. — nvioli, Jan 29 '18 at 20:18

Java Nested If-else shorthand

1 Answers1