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Exception Question

 
Bin Zhao
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Consider the following code:
public class MQ1
{
public static void main(String args[])
{
System.out.println("Before Try");
try
{
}
catch(java.io.IOException t) //1
//catch(Exception t) //2
{
System.out.println("Inside Catch");
}
System.out.println("At the End");
}
}
As //1 showed,this code won't compile with error that no IOException is thrown in try block.
But if //1 is replaced with //2
it compiles without problem.
I can not understand what is behind this.
Please clear it for me
THX
 
Santhosh Kumar
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Posts: 242
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I think you can catch unchecked exception without even throwing in the try block, but there must be some code that throws Checked exception to catch checked exception. Pl correct me if I'm wrong.
Santhosh.
 
Suresh Selvaraj
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Posts: 104
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Hi,
The Exceptions that are declared in a try-catch() block should be of type, java.lang.Exception or java.lang.Throwable or java.lang.Error.
Exception hierarchy:
java.lang.Object
|
+--java.lang.Throwable
|
+--java.lang.Exception
|
+--java.io.IOException
Direct Known Subclasses:
Ex: java.io.EOFException
As you can see java.io.IOException extends java.lang.Exception.
Hence your try-catch() block should be declared to catch exceptions of type Exception/Throwable.
java.io.IOException can be defined in a try-catch() block only if subclasses of java.io.IOException are thrown.
Example:
public class MQ1
{
public static void main(String args[])
{
System.out.println("Before Try");
try
{
throw new java.io.EOFException();
}
catch(java.io.IOException e1) //1
{
System.out.println("Inside IOException");
}
catch(Exception e2) //2
{
System.out.println("Inside Exception");
}

catch(Throwable e3) //2
{
System.out.println("Inside Throwable");
}
System.out.println("At the End");
}
}
The Output of the above code is:
Before Try
Inside IOException
At the End
- Suresh Selvaraj
 
john noronha
Greenhorn
Posts: 1
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I think the answer lies in the fact that while 'Exception' is generic and could be anything (including exceptions like RuntimeException ?), 'IOException' applies to IO related exceptions specifically ? ... just a guess .. would be interested to know for sure

John
Originally posted by Bin Zhao:
Consider the following code:
public class MQ1
{
public static void main(String args[])
{
System.out.println("Before Try");
try
{
}
catch(java.io.IOException t) //1
//catch(Exception t) //2
{
System.out.println("Inside Catch");
}
System.out.println("At the End");
}
}
As //1 showed,this code won't compile with error that no IOException is thrown in try block.
But if //1 is replaced with //2
it compiles without problem.
I can not understand what is behind this.
Please clear it for me
THX

 
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