¿Cómo se realiza una verificación nula de una lista en Java?

How do you do null check for a List in Java?

You should do if(test!= null) instead (Checking for null first). The method isEmpty() returns true, if an ArrayList object contains no elements; false otherwise (for that the List must first be instantiated that is in your case is null ).

A List instance can contain items that represent null .

List isEmpty() method in Java with Examples. The isEmpty() method of List interface in java is used to check if a list is empty or not. It returns true if the list contains no elements otherwise it returns false if the list contains any element.

To check if an ArrayList is empty, you can use ArrayList. isEmpty() method or first check if the ArrayList is null, and if not null, check its size using ArrayList. size() method. The size of an empty ArrayList is zero.

Yes, you can always use null instead of an object. Just be careful because some methods might throw error. It would be 1. itemsList.

HashMap. isEmpty() method of HashMap class is used to check for the emptiness of the map. The method returns True if no key-value pair or mapping is present in the map else False.

You should do if(test!=null) instead (Checking for null first). The method isEmpty() returns true, if an ArrayList object contains no elements; false otherwise (for that the List must first be instantiated that is in your case is null).

Generally, null variables, references, and collections are tricky to handle in Java code. Not only are they hard to identify, but they’re also complex to deal with. As a matter of fact, any miss in dealing with null cannot be identified at compile time and results in a NullPointerException at runtime.

According to the Javadoc for NullPointerException, it’s thrown when an application attempts to use null in a case where an object is required, such as: Calling an instance method of a null object Accessing or modifying a field of a null object Taking the length of null as if it were an array

Since list is an interface, one can’t directly instantiate it. However, one can create objects of those classes which have implemented this interface and instantiate them. Few classes which have implemented the List interface are Stack, ArrayList, LinkedList, Vector etc.