CODEWITHSUNDEEP
javaexception
user2223211
user2223211

Reputation: 165

Java Exception Classes

I am new to Java and I was looking at exception handling. When we catch java exceptions, we declare and use an Object of the Exception class without initializing it, i.e.

catch(NullPointerException e)
    e.printStackTrace();

So my question is, how are we able to use object reference e without instantiating it?

Upvotes: 7

Views: 1328

Answers (4)

Nesan Mano
Nesan Mano

Reputation: 2166

The exception is instantiated. It happens internally in the class that can potentially throw an exception. For your information, the keyword throw is responsible to create and throw the exception. Your catch method will catch the exception. You can also implement your own exceptions using this keyword.

Upvotes: 0

Shailendra Singh
Shailendra Singh

Reputation: 493

Yes, reference e in catch(NullPointerException e) is for the possible exception thrown in code using throw new NullPointerException("some error message");

Upvotes: 0

jlordo
jlordo

Reputation: 37813

They are well instantiated:

void example() {
    throw new UnsupportedOperationException("message");
}      // ^^^

void demonstration() {
    try {
       example();
    } catch (UnsupportedOperationException e) {
        e.printStackTrace();
    }
}

This very simple example should be pretty self explanatory...

Upvotes: 8

Code-Apprentice
Code-Apprentice

Reputation: 83527

The exception is (often) instantiated when the error occurs with a throw statement. For example,

throw new NullPointerException();

(Note that this is just an example. NPEs are not usually explicitly thrown in your own code.)

The catch clause is similar to a function that declares a parameter. Consider the function

void func(String s) {
    // ...
}

func does not instantiate the s. The String is created somewhere else and passed to the function. In the same way, we create an exception with throw and it is "passed" to the catch clause kind of like a parameter.

Upvotes: 1

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