Java：快速/优雅的方式来检查null

Question

In the program I'm currently writing, I find myself doing the following a lot...

Map<String,List<String>> network = loadSerializedObj(file); // null if failed
if(network != null) {
    anonNet = util.anonymize(newNet);
} else {
    // Some sort of error handling.
    System.out.println("Some sort of error message. Exiting...");
    System.exit(0);        
}

Is there a more succinct way of handling the event that loading the serialized object from file doesn't work and the method returns null? Any tips at all are welcome. Anywhere I can make this more elegant?

Answer 1

you should make loadSerializedObj throw an exception instead of return null. you can return null when you don't have anything to return. when something breaks, you should throw an exception.

Answer 2

In this case you can use the exception catch.

Map<String,List<String>> network = loadSerializedObj(file); // null if failed
try {
    anonNet = util.anonymize(newNet);
} catch(NullPointerException npe) {
    System.out.println("Some sort of error message. Exiting...");
    System.exit(0);        
}

but you must specify the util.anonymize to throw the NullPointerException if it does not it yet.

Answer 3

you could have some kind of

class MyAssert {
  static<T> assertNotNull(T object) {
    if (object == null) {
      System.out.println("something is wrong...");
      System.exit(0);
    }
    return object;
  }
}

Answer 4

Try returning an empty map instead of a null value:

    if(!loadSerializedObj(file).isEmpty()) 
    {
        anonNet = util.anonymize(newNet);
    } 
    else 
    {
        // error handling    
    }

    private Map<String,List<String>> loadSerializedObj(File file) 
    {
        // do stuff
        if(mapObject == null)
        {
            mapObject = Collections.emptyMap();
        }
        return mapObject
    }

Answer 5

You could do a static import of a function named n(object) that returns boolean if null. Or use Groovy :)

Answer 6

我认为你所拥有的是在保持易于阅读/维护代码的同时获得的。

Answer 7

番石榴的先决条件可以是一个简洁易读的检查方法。

Preconditions.checkNotNull(myReference, "My error message");