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Why can I throw null in Java and why does it upcast to a NullPointerException?
In Java there is default value for every type, when you don’t initialize the instance variables of a class Java compiler initializes them on your be-half with these values. Null is the default value of the object type, you can also manually assign null to objects in a method.
Object obj = null;
But, you cannot use an object with null value or (a null value instead of an object) if you do so, a NullPointerException will be thrown.
Example
public class Demo {
String name = "Krishna";
int age = 25;
public static void main(String args[]) {
Demo obj = null;
System.out.println(obj.age);
System.out.println(obj.name);
}
}Run time exception
Exception in thread "main" java.lang.NullPointerException at july_set3.Demo.main(Demo.java:11)
Throwing NullPointerException
You can also throw a NullPointerException in Java using the throw keyword.
Example
public class ExceptionExample {
public static void main(String[] args) {
System.out.println("Hello");
NullPointerException nullPointer = new NullPointerException();
throw nullPointer;
}
}Output
Hello Exception in thread "main" java.lang.NullPointerException at MyPackage.ExceptionExample.main(ExceptionExample.java:6
Throwing null value
According to Java documentation a NullPointerException occurs if you try to −
- Call the a method (instance) using null object.
- Access, modify, print, field of a null value (object).
- Trying to access (print/use in statements) the length of null value.
- Throw a null value.
- Accessing or modifying elements/slots of a null value.
Means if you throw a null value a null pointer exception occurs it is not up casting.
Example
public class Demo {
public static void main(String args[]) {
throw null;
}
}Runtime exception
Exception in thread "main" java.lang.NullPointerException at july_set3.Demo.main(Demo.java:5)
Updated on: 02-Jul-2020
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