Today we will learn, What is a NullPointerException, and how do I fix it? So, let’s start:
What is NullPointException
NullPointException is a RunTimeException. NullPointException is thrown when the value of a reference variable or object is null.
When you declare a reference variable (i.e., an object), you are really creating a pointer to an object. Consider the following code where you declare a variable of primitive type
int x; x = 10;
In this example, the variable
x is an
int and Java will initialize it to
0 for you. When you assign the value of
10 on the second line, your value of
10 is written into the memory location referred to by
But, when you try to declare a reference type, something different happens. Take the following code:
Integer num; num = new Integer(10);
The first line declares a variable named
num, but it does not actually contain a primitive value yet. Instead, it contains a pointer (because the type is
Integer which is a reference type). Since you have not yet said what to point to, Java sets it to
null, which means “I am pointing to nothing“.
In the second line, the
new keyword is used to instantiate (or create) an object of type
Integer, and the pointer variable
num is assigned to that
NullPointerException occurs when you declare a variable but did not create an object and assign it to the variable before trying to use the contents of the variable. So you are pointing to something that does not actually exist.
Is it clear?
How to avoid NullPointException?
Please read This article for better understanding:
Hope it helps