Create a new variable and check if it's null in one if

Question

Can I do something like this?

if(variable = class.GetVariable() != null){
    variable.doSomething()
}

As I said in the comments I'm doing this with a HttpSession, so my goal is to check if there is a parameter in the session with a specific name and if it is do something.

`if((variable = class.GetVariable()) != null){`. Parentheses help. — Federico klez Culloca, Sep 09 '19 at 10:55
@HasithaMJayawardana In truth I want to check if the session contains a parameter and if it does I do some code. I just don't want to call the session.getParameter twice because I feel that's a massive waste of resources. — Nuno Mendes, Sep 09 '19 at 10:58
I think it's duplicate https://stackoverflow.com/questions/16148580/assign-variable-value-inside-if-statement[enter link description here](https://stackoverflow.com/questions/16148580/assign-variable-value-inside-if-statement) — dawis11, Sep 09 '19 at 11:00
@dawis11 Yes, it seems to be a duplicate of that question, unfortunately I couldn't find it before. — Nuno Mendes, Sep 09 '19 at 11:01

score 2 · Accepted Answer · answered Sep 09 '19 at 10:55

You can, so long as variable has already been defined and you add additional brackets:

Foo variable;
if ((variable = GetVariable()) != null) {
    variable.doSomething();
}

You tend not to see this pattern often as it's not the most readable, but it is often seen when reading from a BufferedReader line by line (as it provides a convenient, quick way to read lines until there aren't any):

String line;
while((line=reader.readLine())!=null) {
    //Process each line
}

Using `for` you could inline the definition – Grim Sep 09 '19 at 11:02 — Grim, Sep 09 '19 at 11:02

score 1 · Answer 2 · answered Sep 09 '19 at 10:56

!= has precedence over =, so here the code means assigning the boolean value resulting from class.GetVariable() != null to the variable variable :

if(variable = class.GetVariable() != null){
...
}

That is not what you want.
So enclose the assignment between () to set explicitly the precedence :

String variable = null; 
if( (variable = class.GetVariable()) != null){
    variable.doSomething()
}

Grim · Answer 3 · 2019-09-09T11:00:59.910

1

As long as you define the variable first, yes but you must put them in parenties:

MyObject variable;
if( ( variable = class.GetVariable()) != null){
    variable.doSomething();
}

edited Sep 09 '19 at 11:00

answered Sep 09 '19 at 11:00

Grim

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Create a new variable and check if it's null in one if

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