try-catch compile problems

[Cristi Tudose]

These 2 codes are taken from an mock exam:
1.public class AQuestion
{
public static void main(String args[])
{
System.out.println("Before Try");
try
{
}
catch(Throwable t)
{
System.out.println("Inside Catch");
}
System.out.println("At the End");
}
}
2.public class AQuestion
{
public static void main(String args[])
{
System.out.println("Before Try");
try
{
}
catch(java.io.IOException t)
{
System.out.println("Inside Catch");
}
System.out.println("At the End");
}
}
Could someone give me some explanations why code 1 compile without no problem and code 2 complains about no IOException object can ever be thrown.
Thanks in advance.

[Cherry Mathew]

as u knoww there r two types of exceptions checked and unchecked and IOException is a checked exception and java do the checking for this and will know whether it is thrown or not but Throwable is the super class of both checked exceptions and unchecked exceptions so java wont be able to check whether an unchecked exception is thrown inside the block.
i hope this will clear u r doubt
Cherry

[Cristi Tudose]

Thank Cherry
U confirm my suppositions.But I 'm not sure about 1 thinng:in code 2 the parameter for catch clause is IOException,which of course, is a checked exception.At compile time,the java compiler see the handlers for checked exception and in the same time analyse which checked exceptions can result from execution
of try block.The compile error rises here,bcos it couldn't match anything?
I didn't find in JLS a very clear explication.Hope u confirm or not ,if I understand well...
Rgds,
Cristi

[Vladimir Kositsky]

That's right.
Compiler will enjoy expression that throws IOException in try block.

public class AQuestion
{
      public static void main(String args[])
      {
           System.out.println("Before Try");
    try
                {
if( false ){ throw new java.io.IOException();}
                }
                catch(java.io.IOException t)
                {
                System.out.println("Inside Catch");
                }
           System.out.println("At the End");
       }
}