How to Avoid Null Pointer Exception in Java
Null pointer exceptions are errors thrown by the Java compiler when the programmer attempts to use a variable that hasn't been defined. Other compilers, like Visual Basic, allow you to use variables that haven't been defined in the code, but languages like C, C++, C#, and Java do not allow use of a variable without defining it in the code. The following example shows why the error is displayed and how to avoid the error thrown when Java detects a null pointer.
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Instructions
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1
Define some variables. To simulate the error and to show why the exception happens, define some variables to use later in the code:
int i = 2;
int j = 2; -
2
Attempt to add these two variables together and assign them to an undefined variable.
x = j + i;
This throws a null exception pointer because x is not defined in the code. -
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Avoid the null pointer exception by checking if the variable is null prior to using it. The code below avoids the null exception error.
if (x != null) {
x = j+i;
}
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