how to handle nulls gracefully in Java

Question

I have a situation where I have to copy values from one object to another. For each field the copy statement is wrapped with the following snipped of boilerplate code:

if (a.getC() != null) {
   b.setC(a.getC());
}

I had a look at Guava Precondition.checkNotNull(...) but it still throws NPE which I'm trying to evade.

How can I do that in a more natural way?

Is it a problem if the value set by `b.setC` is null? If not, you don't need the null check. The only way this code would throw a NPE is if `a` or `b` was null. — forgivenson, Apr 02 '14 at 13:03

score 1 · Accepted Answer · answered Apr 02 '14 at 13:06

1

Apache commons-lang3 offers this:

b.setC(ObjectUtils.defaultIfNull(a.getC(), b.getC()));

But I have to admit that I'm not sure if this would really be an improvement.

answered Apr 02 '14 at 13:06

Ray

3,084
2
19
27

that fits my needs. Thanks a lot. – user2508615 Apr 03 '14 at 07:30

ubiquibacon · Answer 2 · 2014-04-02T13:11:29.923

1

You could make a method using var args that checks all the args for your if statement:

public boolean argsNotNull(Object ... objs) {
    boolean b = true;
    for(Object o : objs) {
        if(o == null) {
            b = false;
            break;
        }
    }
    return b;
}

Then use it like this:

if(argsNotNull(a)) {
    Object c = a.getC();
    if(argsNotNull(b, c)) { // A null 'c' object may be valid here, depends on your logic
        b.setC(c);
    }
}

Since this method uses var args you can feed it as many args as you want, but it will not work with primitives in its current state.

edited Apr 02 '14 at 13:11

answered Apr 02 '14 at 13:06

ubiquibacon

10,451
28
109
179

This doesn't really solve the problem of `null` checking. It just delegates it to a different method. – Jeffrey Apr 02 '14 at 13:16
@Jeffrey OP asked for more natural. This isn't as nice as say the Groovy [safe navigation operator](http://groovy.codehaus.org/Operators#Operators-SafeNavigationOperator(?.)), but it is better than the alternative of (`a != null && b != null && c != null`) or vast, non-specific try/catch blocks. – ubiquibacon Apr 02 '14 at 13:34

score 0 · Answer 3 · answered Apr 02 '14 at 13:10

Is the b.C value supposed to exactly reflect what is in a.C ? In that case if a.C is null then b.C whould be null, and you don't really need a null check.

Otherwise, to avoid curley braces you could do something like this :

b.setC((a.getC() == null) ? b.getC() : a.getC());

This assumes that the getter and setter from b match up exactly. If C from a is null then setC() from getC() which effectively does nothing.

how to handle nulls gracefully in Java

3 Answers3