[java] Best practice to validate null and empty collection in Java

I want to verify whether a collection is empty and null. Could anyone please let me know the best practice.

Currently, I am checking as below:

if (null == sampleMap || sampleMap.isEmpty()) {
  // do something
} 
else {
  // do something else
}

When you use spring then you can use

boolean isNullOrEmpty = org.springframework.util.ObjectUtils.isEmpty(obj);

where obj is any [map,collection,array,aything...]

otherwise: the code is:

public static boolean isEmpty(Object[] array) {
    return (array == null || array.length == 0);
}

public static boolean isEmpty(Object obj) {
    if (obj == null) {
        return true;
    }

    if (obj.getClass().isArray()) {
        return Array.getLength(obj) == 0;
    }
    if (obj instanceof CharSequence) {
        return ((CharSequence) obj).length() == 0;
    }
    if (obj instanceof Collection) {
        return ((Collection) obj).isEmpty();
    }
    if (obj instanceof Map) {
        return ((Map) obj).isEmpty();
    }

    // else
    return false;
}

for String best is:

boolean isNullOrEmpty = (str==null || str.trim().isEmpty());

We'll check a Collection object is empty, null or not. these all methods which are given below, are present in org.apache.commons.collections4.CollectionUtils package.

Check on List or set type of collection Objects.

CollectionUtils.isEmpty(listObject);
CollectionUtils.isNotEmpty(listObject);

Check on Map type of Objects.

MapUtils.isEmpty(mapObject);
MapUtils.isNotEmpty(mapObject);

The return type of all methods is boolean.

If you use Spring frameworks, then you can use CollectionUtils to check against both Collections (List, Array) and Map etc.

if(CollectionUtils.isEmpty(...)) {...}

If you need to check for null, that is the way. However, if you have control on this, just return empty collection, whenever you can, and check only for empty later on.

This thread is about the same thing with C#, but the principles applies equally well to java. Like mentioned there, null should be returned only if

• null might mean something more specific;
• your API (contract) might force you to return null.

For all the collections including map use: isEmpty method which is there on these collection objects. But you have to do a null check before:

Map<String, String> map;

........
if(map!=null && !map.isEmpty())
......

That is the best way to check it. You could write a helper method to do it:

public static boolean isNullOrEmpty( final Collection< ? > c ) {
    return c == null || c.isEmpty();
}

public static boolean isNullOrEmpty( final Map< ?, ? > m ) {
    return m == null || m.isEmpty();
}

You can use org.apache.commons.lang.Validate's "notEmpty" method:

Validate.notEmpty(myCollection) -> Validate that the specified argument collection is neither null nor a size of zero (no elements); otherwise throwing an exception.

Personally, I prefer to use empty collections instead of null and have the algorithms work in a way that for the algorithm it does not matter if the collection is empty or not.