Type of exceptions in java are checked exceptions and unchecked exceptions. This classification is based on compile-time checking of exceptions. There is also a classification based on runtime in java. It is not widely known! That is synchronous and asynchronous exceptions. First let us see the java checked exceptions and unchecked exceptions.
Checked Exceptions Vs Unchecked Exceptions in Java
At compile time, the java compiler checks that a program contains handlers for checked exceptions. Java compiler analyzes by which checked exceptions can result from execution of a method or constructor.For each checked exception which is a possible result, the throws clause for the method or constructor must mention the class or its superclasses of that exception.
The class RuntimeException and its subclasses, and the class Error and its subclasses are unchecked exceptions classes. Because the compiler doesn’t forces them to be declared in the throws clause. All the other exception classes that are part of Throwable hierarchy are checked exceptions.
Now let us see a see small discussion on why exceptions are classified as checked exceptions and unchecked exceptions.
Those unchecked exception classes which are the error classes (Error and its subclasses) are exempted from compile-time checking in java because they can occur at many points in the program and recovery from them is difficult or impossible.
Example: OutOfMemoryError
Thrown when the Java Virtual Machine cannot allocate an object because it is out of memory, and no more memory could be made available by the garbage collector.
The runtime exception classes (RuntimeException and its subclasses) are exempted from compile-time checking because, in the judgment of the designers of the Java, having to declare such exceptions would not aid significantly in establishing the correctness of programs.
Example: NullPointerException
Thrown when an application attempts to use null in a case where an object is required.
So the java compiler doesn’t forces them to be declared in the above two cases.
Synchronous and Asynchronous Exceptions in Java
The interpreter executes the java program sequentially. An exception E can occur relative to a line (L) of program. That is that exception E will always occur at the execution of that line L. This is called Synchronous exception.
An asynchronous exception in java can occur at any point in the execution of a program.
They occur only as a result of:
- An invocation of the stop methods of class Thread or ThreadGroup
- An internal error in the Java virtual machine
‘this’ keyword in java programs is used to make a call to the constructor of the same class.
‘this’ is a keyword, that is used to call the particular instance.
this(), this with paranthesis is used to call constructor of the same class…!
nice explanation..thanks!! keep up the good work.
Welcome Goutham
Very Nice and So much good explanation of the topic.
So much thanks
PR Chauhan
prchauhan@hotmail.com
welll
good explanantion really helpful
hi,
I just want to know one thing in exception handling mechanism. FileNotFound is a checked exception.It means we are handling at compile time.But it is caught at run time when program executes. How a JVM will decide which none is Checked exception and Which one is Unchecked exception.
Can you explain the whole scenario of Exception handling ?
Thanks
Sandy
Hi joe,
Very nice explonation…
I am very new to java.. can you please suggest me whcih books do i need to refer for java,Servlets and JSPs..
Hi varun , You can go for HeadFirst Series for referring and learning Java . And also some good blogs .
Checked Exceptions are exceptions that are handled by the compliler compile time.But it is caught at run time when program executes. How a JVM will decide which one is Checked exception and Which one is Unchecked exception.
yesterday i was asked the same question. But i could not answer it. But really this is a nice explanation. And i got the answer.
Thanx a lot buddy…
very nice………
excellent explaination i love this site..
plz put some sample example
checked exception are those exception which are declare as already it simple mean if we compile our program then it shows a specified exception …..eg.
import static java.lang.System.*;
import static javax.lang.Timer .*;
using this packade we get the checked exceptipon error .it give CE error
Nice Explanation
Nice Explanation, Keep Up The Good Work – Thanks !!
nice example
it’s nice. very good. at the same time little bit depth is required
how compiler find in comilation time whether that exception is checked or unchecked… can anyone help me about that??
is not a correct explanation.
Today I understood the diff b/w checked, unchecked exceptions.. good article for beginners.
Excellent explanation. Keep going on…….
nice but some missing
please checked this url
http://tutorials.jenkov.com/java-exception-handling/checked-or-unchecked-exceptions.html
hi joe,
i am a java student, i want to know that what
is java native interface(JNI)….
Checked exceptions are actually incredibly convenient. It kills me when I see other programmers catch the superclass and do something generic when they could do something specific to handle the various exceptions they might get.
I also am discouraged by .NET code that has try/catch littered at various parts in a huge block of code that more or less act as continue statements in a foreach.
Java can be a slow and painful beast, but they did at least make it easy to put some love into your exception handling. Much encouraged, and very appreciated to your maintainers when you do!
I also feel very bad when people use exception handling for flow control.
There is a wrong statement. Java is not slow. If you say so, you might be using jdk1.2 or less. Latest versions compete on par with C with respect to performance.
very useful………..thanks
by
Meda……
Thanks for this information. Nice work.
Thank you so much……
Thanks for knowledge about checked and unchecked exception…….
Thank u very much..
yes its really a good explanation.
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sir i was inot able to understand it can u explain it in a much more simpler way like i have mmy exam on 17th
its really nice notes
I am not happy with the diff given between checked ad unchecked exceptions.You should give some examples abt the same and explain.
I m a c language & faculty following yr blog cont. to learn java. Please do the needful…
your post are really nice..
one small suggestion have tabular format comparison for differece description. :)
Thanks,
vennila
sir u need to more describe Synchronous and Asynchronous Exceptions in Java.And Checked Exception.
nice work really its soo nice
Great work joe keep it up it has helped me a lot my java examination questions
it is too short try make some extra matter in exceptions,present it is useful of me.Thankyou.
NIce Job and is Very HelpFul to all Of us
Hai sir,
How compiler find in compilation time whether that exception is checked or unchecked… can anyone help me about that??
import java.util.Scanner;
class std{
int mark;
public void get()
{
Scanner a=new Scanner(System.in);
System.out.println(“Enter the Number:”);
mark=a.nextInt();
}
public void set()
{
if(mark=50 && mark<=60)
System.out.println("Pass class");
}
public static void main(String args[])
{
new std().get();
new std().set();
}
}
Explain this program plz the result is not getting perfect
check the condition if it is not a typing mistake….
“if (mark==50…)”
hi,
how jvm will identify,which is one is checked,unchecked exception.and filenotfound exception is a checked exception but this will happen at run time.please clarify my doubt
Hi Joe,
I have a doubt in this…Runtime Exceptions and Erros can’t be caught in compile time so it may fall under Synchronous or Asynchronous exceptions rite???please clarify my doubt..
Hi,
Can u explain me what is IO Exception??
and when will we use it??
What happens if we have same mapping in multiple struts-config? Which one gets loaded?
Good. Well done blog.
Yes it is very useful for me…
Thanks a lot…
Well explained!!!
Very nice explanation!!
Guys please refer the “Java language Specfication ” Book many times for more.
sir,
i have a question…sir we know that jvm throw an object on our programe of exception that is expose in our programe..
But in checked exception the compiler declare exception without the help of jvm..how..??
Good One!
This is my blog on exception..
http://anexceptionviewinjava.blogspot.in/
Good one. It is really helpful to me…..
i like d blog
i like d blog
Its really nice. Easy to understance. thanks a lot joe..
i want to know about interfaces….why we really need it?
means my question is in interfaces we can only define method declaration after that we have to again define in the class for their defination.
we can do directly this thing why two times writing ?
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nice,
very useful…
realy nice explanatn..
and in easy lang…
thank u..
Good One!
Can a checked exception be handled without a catch block, using only finally block?
if yes, why?
How to convert unchecked exception to checked one and under what are conditions this can be done as we know spring and hibernate is based on this.
very intersting
Why do we need to declare a checked exception?