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Java : Null Pointer Exception

What is a Null Pointer Exception?
Thrown when an application attempts to use null in a case where an object is required. These are the common scenarios where one can confront with a null pointer exception:-
  • Obtaining the length of such object as an array which is null.
  • Invoking an instance method of a object which is null.
  • Accessing or modify a particular field of a object which is null.
–       
       Package Structure:
 
ava.lang.Object—>java.lang.Throwable—>java.lang.Exception—>
java.lang.RuntimeException—>java.lang.NullPointerException
Example,
String a = null;
System.out.println(a.toString());
Handling Null Pointer Exception,
  • Check each object for null before using it in the code.
  • Check the passing parameter to a method for null value before using it in your code. Throw    IllegalArgumentException type for parameters with null values to the method.
                  public void method(Object object) {
                            if (object == null) {
                                throw new IllegalArgumentException(“Null Values not allowed”);
                              }
                    }
  • Use of primitive type wherever possible (int instead of Integer).
                  int a=5;       /* avoid use of new Integer(5)*/
  •  Use String.valueOf instead of toString as valueOf is a static method while toString works on objects.
  • Do not return any null value from a method; instead return an empty object of the return type.
                     public student matchCriteria(){
                             return new Student(;)/* avoid return null;  */
                       }
  •  Use of constant first during equal comparison, like
            “Sandeep”.equal (inputname).
If you look into the src folder of jdk the then you can see the definition of this NullPointerException
public class NullPointerException extends RuntimeException {
                public NullPointerException() {
                                super();
                }
                public NullPointerException(String s) {
                                super(s);
                }
}    
NullPointerException object is a type of RuntimeException.

Sandeep
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Sandeep

A passionate Blogger and Developer.Love to code for web application using JavaScript.At present I am exploring the Web Component Specification.

12 years ago java417