How to avoid null pointer exception in Java?
I am trying to use a Java HashMap. Using map.get (“A”) to get a value for a key from the map resulted in a NullPointerException. Then I used if (map.get (“A”)) to avoid a NullPointerException being thrown, but it gets thrown anyway.
When do hashmaps throw the null pointer exception?
If nextLine [0] and nextLine [6] aren’t null, because the println call above worked, then that leaves dataMap. Did you do dataMap = new HashMap (); somwehere? My case was different as Usually, hashmaps throw the null pointer exception when trying to read a key that is not there e.g I have a
Why is the null pointer to the map null?
map itself is null because you never initialized it. map is declared as Map map. If this is the case, then your if statement doesn’t do what you think it does. It actually gets the Boolean object from the map and tries to unbox it to a primitive bool.
Do you declare a variable or set it to null?
To clarify, you declare the variable and set it to null. But you need to instantiate a new Map, whether it’s a HashMap or similar. dataMap is declared but not initialized. It can be initialized with
To avoid the NullPointerException, we must ensure that all the objects are initialized properly, before you use them. When we declare a reference variable, we must verify that object is not null, before we request a method or a field from the objects.
What causes the NullPointerException to be thrown?
NullPointerException is thrown when program attempts to use an object reference that has the null value. These can be: Invoking a method from a null object. Accessing or modifying a null object’s field. Taking the length of null, as if it were an array. Accessing or modifying the slots of null object, as if it were an array.
How to invoke a method from a null object?
Invoking a method from a null object. Accessing or modifying a null object’s field. Taking the length of null, as if it were an array. Accessing or modifying the slots of null object, as if it were an array. Throwing null, as if it were a Throwable value.
What is the use of null in Java?
Null is a special value used in Java. It is mainly used to indicate that no value is assigned to a reference variable. One application of null is in implementing data structures like linked list and tree.