Clean way of handling null pointers when using arrays

Question

I have the following code which is adding somestrings to an arraylist. It will ever so often have an empty variable due to someone not filling it in correctly. I don't own the usr object so I can't modify it unfortunately. Is there a clean and easy way of just adding a default value if one of these values is empty? I don't mind if its empty, but I don't want the program to crash out!

    results.add(usr.getName());
    results.add(usr.getAbout());
    results.add(usr.getBirthday());
    results.add(usr.getEmail());
    results.add(usr.getGender());

Not sure, what is the type of results, seems it must be generic Collection. One of the elegant ways to handle nulls is to have your own subclass of List (or other Collection), which will handle adding null's as you wish. — Victor Sorokin
– Victor Sorokin, Commented Aug 31, 2010 at 17:31

Jeff Storey · Accepted Answer · 2010-08-31 18:02:15Z

4

You just have to check if the values are null.

String name = usr.getName();
if ( name != null ) {
   results.add(name);
}

You can do this for each of the values. You can use a shorter syntax like

results.add(usr.getName() != null ? usr.getName() : "");

Though that requires calling getName twice, it shouldn't matter since I assume that is just a simple getter.

Edit #1

If you don't want to check for null on every check, you can use a reflection based solution. This example is groovy based, and while I do think it's overkill for a few values, if you have a lot of values, it might make more sense.

results.add(getValue(usr,"name"))
results.add(getValue(usr,"about"))

String getValue(def usr, String prop) {
   return usr."${prop}" ?: ""
}

edited Aug 31, 2010 at 18:02

answered Aug 31, 2010 at 17:26

Jeff Storey

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3 Comments

Steve Over a year ago

Ah I dont want to have an if statement for each individual string to see if its there or not. I find it kind of dirty to read. But if its the only option then I;ll have to use that

Jeff Storey Over a year ago

@Steve, as others stated though, you could always remove the nulls at the end (but I prefer not to have nulls in the list at all).

Jeff Storey Over a year ago

@Steve, also see Edit #1 for some other possibilities.

Peter Tillemans · Accepted Answer · 2010-08-31 21:16:22Z

1

If you need this often you could make a Cleaner class like :

package com.acme.util;

class Cleaner {

    public static String clean(String s, String defaultValue) {
        return s == null ? defaultValue : s;
    }

    public static Integer clean(Integer v, Integer defaultValue) {
        return v == null ? defaultValue : v;
    }

    public static Date clean(Date d, Date defaultValue) {
        return v == null ? defaultValue : d;
    }

    // ... and so on ...

}

and then use is as :

import static com.acme.util.Cleaner.*;

results.add(clean(usr.getName(),"John Doe"));
...

I do not like static imports but I like null checks everywhere even less.

Ricky Clarkson pointed out this can be expressed even shorter using generics as :

public static <T> T getOrElse(T t, T defaultValue) { return t == null ? defaultValue : t; }

edited Aug 31, 2010 at 21:16

answered Aug 31, 2010 at 17:36

Peter Tillemans

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5 Comments

BalusC Over a year ago

Note that default is a reserved keyword in Java (used in switch statements).

Peter Tillemans Over a year ago

Oops.... thanks for point it out. I fixed it. I cannot remember when I last used a switch statement....

Ricky Clarkson Over a year ago

public static <T> T getOrElse(T t, T defaultValue) { return t == null ? defaultValue : d; } -- No need to repeat yourself.

Steve Kuo Over a year ago

Package names should be all lowercase in Java.

Marimuthu Madasamy Over a year ago

@Ricky Clarkson Thats the nice one. I also thought the same solution. I think you can post that as an answer.

Justin Niessner · Accepted Answer · 2010-08-31 17:26:33Z

0

Check for a null return value inline and then replace the null with a default value all using the conditional operator:

results.add(usr.getName() != null ? usr.getName() : "default");

answered Aug 31, 2010 at 17:26

Justin Niessner

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Comments

Carl Manaster · Accepted Answer · 2010-08-31 17:28:08Z

0

If you want a List that reads null as - say - the empty string, you could write a class that implements List and delegates most every call to an internal ArrayList, but in the case of add(), first checks for null. You could also just subclass ArrayList, but that's generally considered a bad idea.

answered Aug 31, 2010 at 17:28

Carl Manaster

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Comments

Colin Hebert · Accepted Answer · 2010-08-31 17:30:56Z

0

It seems that you don't want theses values at all, and having an empty string doesn't lead to anything. If you just want to have a null-free List, either you check each value to avoid any null value in your List, or you can remove any null value in your array after every value has been added :

result.remove(null);

An even better thing to do, is understand why your program craches. Maybe you could check for null values when you read everything in your List.

Resources :

Javadoc - List.remove()

edited Aug 31, 2010 at 17:30

answered Aug 31, 2010 at 17:25

Colin Hebert

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