asked on

Java Exception example issues

if we are multiple catch taking from
parent to child then why we will get Compile time error saying

exception zzz has already been caught

class TestException {
	public static void main(String[] args) {
		System.out.println("st1");
		try {
			System.out.println(10 / 0);
		} catch (Exception e) {
			System.out.println(100 / 2);
		}catch (ArithmeticException e) {
			System.out.println(100 / 2);
		}
		System.out.println("st3");
	}
}

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above gives different error as below for some reason?
No exception of type Exception can be thrown; an exception type must be a subclass of Throwable
Not sure what it means by above compilation error?
where below code running fine

class TestException {
	public static void main(String[] args) {
		System.out.println("st1");
		try {
			System.out.println(10 / 0);
		} catch (ArithmeticException e) {
			System.out.println(100 / 2);
		}
		System.out.println("st3");
	}
}

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ASKER CERTIFIED SOLUTION

jglete

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SOLUTION

HemanthaKumar

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gudii9

ASKER

class TestException {
	public static void main(String[] args) {
		System.out.println("st1");
		try {
			System.out.println(10 / 0);
		} catch (ArithmeticException e) {
			System.out.println(100 / 2);
		}
		System.out.println("st3");
	}
}

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i only see ArithmeticException but not exception?

how to and where to interchange?please adivse

jglete

class TestException {
	public static void main(String[] args) {
		System.out.println("st1");
		try {
			System.out.println(10 / 0);
		} catch (ArithmeticException e) {
			System.out.println(100 / 2);
		} catch (Exception e) {
                        System.out.println("Not expected exception");
               }
               System.out.println("st3");
	}
}

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Always order your exceptions from the more detailed exception to the more generalist.

HemanthaKumar

jglete got the idea..

gudii9

ASKER

I got it now.
but what compiler says seems different to me?

above gives different error as below for some reason?
No exception of type Exception can be thrown; an exception type must be a subclass of Throwable
Not sure what it means by above compilation error?

what above error means? it is not clear

jglete

Try using java.lang.Exception instead of Exception.

If this works, then you have another class Exception in your CLASSPATH, or in the same directory.

Perhaps you were testing exceptions in java and you made a class named exactly Exception.java in your current directory.

If this is the case, I advise you to use another name for that class (like ExceptionTest or similar).

gudii9

ASKER

Try using java.lang.Exception instead of Exception.

where i see i had mistakenly named a class as Exception which seems bad thing to do?
I corrected that now and renamed it to ExceptionCls

gudii9

ASKER

now compiler happy

class TestException {
      public static void main(String[] args) {
            System.out.println("st1");
            try {
                  System.out.println(10 / 0);
            } catch (ArithmeticException e) {
                  System.out.println(100 / 2);
            }catch (Exception e) {
                  System.out.println(100 / 2);
            }
            System.out.println("st3");
      }
}

gudii9

ASKER

public class ExceptionCls {
	
	public static void myMethod(Object x) throws Exception  {
	   if (x == null)
		      throw new Exception("worst input") ;
		}

		public static void main(String[] args) throws Exception {
		    myMethod(null) ;
		}
		
}

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Exception in thread "main" java.lang.Exception: worst input
at ExceptionCls.myMethod(ExceptionCls.java:6)
at ExceptionCls.main(ExceptionCls.java:10)

why i forced to use throws keyword 2 times one at main method one other at myMethod?
please advise

jglete

Any Exception that isn't from the tree of RuntimeException has to be thrown.

You have to do it twice, because each method in the call stack is required to do that.