Need help to write - null check for objects

[Renee T]

Dear All,

 

I need your help to write the below custom rule. I need a null check rule for an object, before we retrieve values from an object.

 

eg:
Class Foo{

int A;
String B;
.
.
}

if (foo.getA() > 5){
}

If any operation is done on the object without a null check, it has to be highlighted and logged..
Thanks in anticipation!

[Roman Ivanov]

Please write exact and compilable code as examples. Please provide example of code that you think is correct and few codes that are not correct. In each incorrect example please write trailing single line comment. Also provide message you thinks is appropriate.

Thanks,
Roman Ivanov

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[Renee T]

Hi,

 

PFB example:

 

public class Foo{
  int A;

  public int getA() {
    return (5);
  }

public void check(){

 Foo foo = new Foo();
 Foo bar = new Foo();
 
    // missing null check should show a violation
    if (foo.getA() > 5){ }
    // missing null check should show a violation
    if (bar != null && foo.getA() > 5) {}
    // correct null check
    if (foo != null && foo.getA() > 5) { }
  }
}

 

Thanks.

[Roman Ivanov]

Hi Renee,

please be aware that Checkstyle can not distinguish types , and does not aware about their hierarchy. All you have is tree of String values.

so you need to listen in Check specified by you type creation ("new" operator) or method parameters.

After that traverse tree below yourself and search for variable usage and detect "variable != null".

Just take a look at other Checks for examples how it it possible to be done. 

I think similar functionality is there - https://github.com/checkstyle/checkstyle/blob/master/src/main/java/com/puppycrawl/tools/checkstyle/checks/coding/VariableDeclarationUsageDistanceCheck.java

thanks,

Roman Ivanov

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