Related to Exceptions

[Prince Chauda]

Why this code produces compile time error - exception java.io.FileNotFoundException is never thrown in body of corresponding try statement

import java.io.*;
public class pin {
	void a(){
		try{
			
	       }
		catch(FileNotFoundException e){} //  or catch(NoSuchMethodException e){}
		
	}

    public static void main(String as[])throws IOException
    {
    	
    }
    
}

while this one doesn't

import java.io.*;
public class pin {
	void a(){
		try{
			
	       }
		catch(Exception e){}
		
	}

    public static void main(String as[])throws IOException
    {
    	
    }
    
}

[Henry Wong]

In the first case, you are catching a checked exception -- the compiler can actually check to see if the exception is actually thrown, and hence, complain if it isn't.

In the second case, the Exception class is a super class for many exceptions. Including the RuntimeException class, which is an unchecked exception. These are a class of exceptions which can be thrown at any time, by the JVM.... takes a breath.... Since, the compiler can't confirm that an unchecked exception won't be thrown, and since, the Exception class is a super class of unchecked exceptions, it is allowed.

Henry

[Tom Johnson]

Because the compiler can see that FileNotFoundException cannot be thrown from the method as its a checked exception. The second snippet catches the parent class Exception, which will catch both checked and unchecked exceptions. So there is a chance (as far as the compile is concerned) that a runtime (unchecked) exception could occur in the try block, even though its empty. Hence the second one is allowed.

[Tom Johnson]

D'oh just in before me Henry