Doubt in Exception

[sanjeevtarar]

Hello All,

I have one doubt in Exception in Java.

Can we catch every Exception and Error in our program using try catch block?


please give some thought.

[Eranga]

Ya, I think so. If we write our own Exceptions correctly, it's ok. Did you try to do it in any other way?

[sanjeevtarar]

Yes pal ,

try this example.

I have one java file named CheckException.java(very simple) It's compiling fine.
I have saved this file with the same name as class name as usual but when i change class name to CheckException1 and try to compile it gives error on command prompt :CheckException.java:1: class CheckException1 is public, should be declared in a file named CheckException1.java ..... as usual it will give, this is OK.

Now i created another class Named TestCheckException.java in which using Runtime i am compiling CheckException.java by changing the class name to CheckException1(in CheckException.java), and putting code in try catch......but i am not able to catch the Exception or Error.

Try to run these example.

CheckException.java

public class CheckException1 
{
	public static void main(String[] args){
		System.out.println("in CheckException...");
	}
}

TestCheckException.java

import java.io.*;

public class TestCheckException 
{
	public static void main(String[] args){
		try{
			
			Process proc = Runtime.getRuntime().exec("javac CheckException.java");

		}catch(Exception err){  // or use catch(Throwable err)
			System.out.println("ERROR...."+err);
		}
	}
}

[Eranga]

Ok, I'll try it. But one thing. Why did you execute the CheckException.java, rather CheckException1.java?

[sanjeevtarar]

Ok, I'll try it. But one thing. Why did you execute the CheckException.java, rather CheckException1.java?

Just to get the exception and to check this....R&D only.

[Eranga]

Can you execute a command line argument using Process in Java? :) For me I got the exception as "ERROR....Cannot run program "javac": CreateProcess error=2, The system cannot find the file specified"

So...

[sanjeevtarar]

Where did you get this ..... in TestCheckException.java file....

but i am not getting this.... program running fine

[Eranga]

From your code pal. That's ok, isn't it. Exception point that javac can't run as a process. That's why I'm asking it....???

[sanjeevtarar]

But i am not getting dear
can please detail some more about this

[Eranga]

For the min change the process execution line for other file which you don't have in the working package. Maybe like this,

Process proc = Runtime.getRuntime().exec("javac sanjeev.java");

I assume that, there is no such a file. ;) What error message you got?

[sanjeevtarar]

I am not getting any error message............

[Eranga]

I can't be happened my friend. Just run the TestCheckException class. You should get the error.

[sanjeevtarar]

I am running this file as you told me.

but i am not getting any error message on console

import java.io.*;

public class TestCheckException 
{
	public static void main(String[] args){
		try{
			
			Process proc = Runtime.getRuntime().exec("javac sanjeev.java");

		}catch(Exception err){  // or use catch(Throwable err)
			System.out.println("ERROR...."+err);
		}
	}
}

[Eranga]

It wont be pal. Try it with IOException. Which IDE you use.

[sanjeevtarar]

It wont be pal. Try it with IOException. Which IDE you use.

I used Exception class then .....there is no need for IOException
well i also used IOException but nothing changed.
Using Notepad and compiling using Console(Command Prompt on Windows).

[sukatoa]

Have you check the javac classpath eranga? (just to confirm)...

[danielstoner]

Eranga, you get this error (ERROR....java.io.IOException: Cannot run program "javac": CreateProcess error=2, The system cannot find the file specified) because the javac executable is not in the system path. If you specify the full path you will get no exception because the code finds javac and executes it.

Sanjeev - not getting an exception is normal because none is thrown. You are executing another process and even if that process gets errors you don't check for them. You have to manage the started process and know its interfaces to get the errors. On the other hand if you would run the Java compiler programmatically, then you would get an exception because your target Java file is not there.

[Zosden]

If you just want to catch all exceptions just

try
{
   what ever you want to test

}
catch(Exception e)
{ 
    e.printStackTrace();
}

[Eranga]

Have you check the javac classpath eranga? (just to confirm)...

Oops, I forget it. Just work on Netbeans and forget to do it. Thanks for pointing me.

[Eranga]

If you just want to catch all exceptions just

try
{
   what ever you want to test

}
catch(Exception e)
{ 
    e.printStackTrace();
}

Yes, but sanjeev work on his own exception class there. Stack trace always give a quite well explained exceptions.