Java: Initialize condition in If construct (performance)

Question

I am looking for a possibility to initiate a variable in the if condition, so it is only valid in the scope of the condition.

Example: I want to transform this:

String tmp;
if ((tmp = functionWithALotOfProcessingTime()) != null)
{
    // tmp is valid in this scope
    // do something with tmp
}
// tmp is valid here too

Into something similar like this:

if ((String tmp = functionWithALotOfProcessingTime()) != null)
{
    // tmp is *ONLY* in this scope valid
    // do something with tmp
}

The compiler will automatically limit the scope of a variable to where it is used. BTW This has no impact on performance, only only limiting the use of a variable to where it is intended to be used. — Peter Lawrey
– Peter Lawrey, Commented Dec 8, 2014 at 10:42

Kent · Accepted Answer · 2014-12-08 10:28:38Z

3

I can think of two ways to do it:

You need an extra scope, {...} or try{...}catch... and declare the tmp in that scope.
wrap your if logic in a private method, and declare the tmp in the method, so that in your main logic, you cannot access tmp

answered Dec 8, 2014 at 10:28

Kent

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Comments

Ankur Shanbhag · Accepted Answer · 2014-12-08 10:29:21Z

2

Try something like this:

{
    /*
     * Scope is restricted to the block with '{}' braces 
     */
    String tmp; 
    if ((tmp = functionWithALotOfProcessingTime()) != null) {
        // tmp is valid in this scope
        // do something with tmp
    }
}

tmp = "out of scope"; // Compiler Error - Out of scope (Undefined)

edited Dec 8, 2014 at 10:29

answered Dec 8, 2014 at 10:23

Ankur Shanbhag

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4 Comments

Eun Over a year ago

I don't want an extra scope, it messes up the readability of the code

Ankur Shanbhag Over a year ago

In that case, its not doable with if blocks. Scope is just an alternative.

xehpuk Over a year ago

@Eun You clearly want an extra scope, and in Java you do it with the braces.

Eun Over a year ago

Accepted, since it is the closest answer, btw I know what I want and what I don't.

Marko Topolnik · Accepted Answer · 2014-12-08 10:50:02Z

1

I suggest leveraging the Optional API:

Optional.ofNullable(functionWithALotOfProcessingTime()).ifPresent(tmp -> {
   // do something with tmp
});

Note: Optional was introduced in Java 8.

answered Dec 8, 2014 at 10:50

Marko Topolnik

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