Can you store a variable inside a if-clause?

Question

I\'m kinda waiting for a \'no\' answer on this question.

I was interested if you can save a variable at the same time when you checking it in an if-clause.

Answer 1

From the department "My Programming Language is Better Than Your Programming Language": In Groovy, you can use the "?." operator:

Bar bar = foo?.bar
if (bar != null) {
}

In Java, this is good pattern(*):

Bar bar = foo == null ? null : foo.getBar();
if (bar != null) {
}

*: Something you can save in your fingertips.

Answer 2

if you want to limit the scope of Bar bar I'd add { and } around the code that Michael posted.

void foo()
{
    // some code ...

    // this block limits the scope of "Bar bar" so that the rest of the method cannot see 
    // it.
    {
        Bar bar;
        if(foo!=null && (bar = foo.getBar())!=null){
            System.out.println("Success: " + bar);
        } else {
            System.out.println("Failiure.");
        }
    }
}

You might also want to check into the null object pattern if it makes sense. I personally try to avoid things being null if I can... really think about if you want null to be allowed or not.

Answer 3

Actually I think that is a way to do this using Java Optional, here's an example:

Optional.ofNullable("text").ifPresent( $0 -> {
  System.out.println($0.toUpperCase());
});

Or in your case:

  if(foo != null){
      Optional.ofNullable(foo.getBar()).ifPresent(bar -> {
          System.out.println("Success: " + bar);
      });
  }

Answer 4

This is the closest you can get:

Bar bar;
if(foo!=null && (bar = foo.getBar())!=null){
  System.out.println("Success: " + bar);
} else {
  System.out.println("Failiure.");
}

Answer 5

Three points that completely fail to answer the question:

null is evil. Don't write methods that return it. Your example problem would then disappear.

I think you might be missing out on encapsulation. Instead of foo.getBar() could the interface of foo be made such that you perform a "tell don't ask" operation?

Side-effects in expression tends to cause bad code. Prefer more, simpler lines to fewer, buggy lines. The usual exception if using ++ to increment an index when accessing a buffer, or similar iterator style algorithms.

Answer 6

I have used that technique when iterating over lines from a BufferedReader:

BufferedReader br = // create reader
String line
while ((line = br.readLine()) != null) {
    // process the line
}

So yes, you can do an assignment, and the result off that will be the left hand side variable, which you can then check. However, it's not legal to declare variables inside a test, as they would then only be scoped to that expression.