Null Pointer Exception adding null check

Question

Simple and best way to solve Null pointer exception at this line:

oS = ((SyIntBVO)syIntBVOList.get(0)).getSource().trim();  

Exception on getSource variable. how to add null check?

Answer 1

String oS = ((SyIntBVO)syIntBVOList.get(0)).getSource();

if(os != null) {
    os = oS.trim(); // we're good
} else {
    // deal with null
}

Or, if get(0) returns null, this will work:

SyIntBVO syIntBvo = ((SyIntBVO)syIntBVOList.get(0));

if(syIntBvo != null) {
    String os = SyIntBvo.getSource().trim(); // we're good
} else {
    // deal with null
}

To decide which one you need we require more details, e.g. a stack trace.

Answer 2

Depending on how "defensive" you need your code to be, technically you could need to check for null on anything that potentially could be null. At the extreme case, this is any object you de-reference. For example...

Can syIntBVOList be null? Then you need to check it before you de-reference it:

if (syIntBVOList == null) {
    return;
}
SomeType variable = syIntBVOList.get(0);

Can variable be null? Can its casted version be null?

SyIntBVO anotherVariable = ((SyIntBVO)variable);
if (anotherVariable == null) {
    return;
}

Can getSource() return null? Same pattern. And so on...

It's really up to your code what can or can not potentially be null. If any of these instances of an object, whether stored in a variable or referenced directly in-line, can be null then you would want to check for that null reference before de-referencing it.

(Note: It's often considered an anti-pattern for a method which should return an instance to sometimes return null. For exactly this reason, because it requires consuming code to be this defensive.)