Printing the stacktrace

[pjerald]

I get the code from our articles for exception.
I just modified the code and tried to run it.
But it scold me..as follows.

MyException.jav a:44: 'void' type not allowed here
System.err.prin tln("test : "+e.printStackT race());
^
1 error



Kindly read the program...

package test;

public class MyException
{
public void calculate(double a, double b, char func) throws Exception
{
	double result;
	switch(func)
	{
		case '+' : result = add(a,b); break;
		case '-' : result = sub(a,b); break;
		case '*' : result = mul(a,b); break;
		case '/' : result = div(a,b); break;
		default  : result = 0;
	}
	System.out.println(a + " " + func + " " + b + " = " + result);
}
public double add(double a, double b)
{
	return a+b;
}
public double sub(double a, double b)
{
	return a-b;
}
public double mul(double a, double b)
{
	return a*b;
}
public double div(double a, double b) throws Exception
{
	if (b==0) throw new Exception();
	return a/b;
}
public static void main(String args[])
{
	MyException obj = new MyException();
	try
	{
	obj.calculate(2.3,3.4,'+');
	}
	catch(Exception e)
	{
		System.err.println("test : "+e.printStackTrace());
	}
}
}

Awaiting for response,
Pjerald

[pjerald]

What is wrong with me...

I get the code from our articles for exception.
I just modified the code and tried to run it.
But it scold me..as follows.

MyException.jav a:44: 'void' type not allowed here
System.err.prin tln("test : "+e.printStackT race());
^
1 error



Kindly read the program...

package test;

public class MyException
{
public void calculate(double a, double b, char func) throws Exception
{
	double result;
	switch(func)
	{
		case '+' : result = add(a,b); break;
		case '-' : result = sub(a,b); break;
		case '*' : result = mul(a,b); break;
		case '/' : result = div(a,b); break;
		default  : result = 0;
	}
	System.out.println(a + " " + func + " " + b + " = " + result);
}
public double add(double a, double b)
{
	return a+b;
}
public double sub(double a, double b)
{
	return a-b;
}
public double mul(double a, double b)
{
	return a*b;
}
public double div(double a, double b) throws Exception
{
	if (b==0) throw new Exception();
	return a/b;
}
public static void main(String args[])
{
	MyException obj = new MyException();
	try
	{
	obj.calculate(2.3,3.4,'+');
	}
	catch(Exception e)
	{
		System.err.println("test : "+e.printStackTrace());
	}
}
}

Awaiting for response,
Pjerald

[JosAH]

The printStackTrace method doesn't return anything (void) so it can not be used
in an expression. Just use it as a statement.

kind regards,

Jos

[r035198x]

e.printStackTra ce() is void but you are trying to use it as a right operand for the + operator.
Open the API docs for Exception and you'll see all the methods that return Strings. Just pick one that you want.

[pjerald]

AAhhaa I got it. Thank you jos.
But still i dont understand why it does not work first.
I just enclosed e.printStackTra ce() in double quotes,

Apology.

Sorry for the double posting.


Thanks and Regards,
P.Jerald

[r035198x]

AAhhaa I got it. Thank you jos.
But still i dont understand why it does not work first.
I just enclosed e.printStackTra ce() in double quotes,

Apology.

Sorry for the double posting.


Thanks and Regards,
P.Jerald

I've merged the threads.
Read the replies again to see why it didn't work at first.

[JosAH]

AAhhaa I got it. Thank you jos.
But still i dont understand why it does not work first.
I just enclosed e.printStackTra ce() in double quotes,

I don't understand that remark: if you put something between double quotes
you're effectively turning it into a String which can be printed.

kind regards,

Jos

[pjerald]

I don't understand that remark: if you put something between double quotes
you're effectively turning it into a String which can be printed.

kind regards,

Jos

Ya I know. But if i not put a try catch it scolds me like this,


MyException.jav a:38: unreported exception java.lang.Excep tion; must be caught or declared to be thrown
obj.calculate(2 .3,3.4,'+');
^
1 error
2.3 + 3.4 = 5.6999999999999 99


For this reason i put a try and catch.

[JosAH]

Ya I know. But if i not put a try catch it scolds me like this,


MyException.jav a:38: unreported exception java.lang.Excep tion; must be caught or declared to be thrown
obj.calculate(2 .3,3.4,'+');
^
1 error
2.3 + 3.4 = 5.6999999999999 99


For this reason i put a try and catch.

I don't understand what it's all about anymore: first you're talking about putting
things in double quotes and now you're talking about something completely
different. Your div method throws an Exception so your calculate method throws
an exception so you must either handle it or declare that you throw it yourself.

kind regards,

Jos

[pjerald]

Ya I know. But if i not put a try catch it scolds me like this,


MyException.jav a:38: unreported exception java.lang.Excep tion; must be caught or declared to be thrown
obj.calculate(2 .3,3.4,'+');
^
1 error
2.3 + 3.4 = 5.6999999999999 99


For this reason i put a try and catch.

Yes i got it. Thank you friends.
Thanks,
P.jerald

[JosAH]

Ya I know. But if i not put a try catch it scolds me like this,


MyException.jav a:38: unreported exception java.lang.Excep tion; must be caught or declared to be thrown
obj.calculate(2 .3,3.4,'+');
^
1 error
2.3 + 3.4 = 5.6999999999999 99

For this reason i put a try and catch.

Yes i got it. Thank you friends.
Thanks,
P.jerald

You do realize that you're talking to yourself now don't you? ;-)

kind regards,

Jos

[pjerald]

You do realize that you're talking to yourself now don't you? ;-)

kind regards,

Jos

mmmm your are right.
All because of my poor knowledge in java.

I wish to be an expert like you in java.


Thanks,
P.Jerald

[pjerald]

mmmm your are right.
All because of my poor knowledge in java.

I wish to be an expert like you in java.


Thanks,
P.Jerald

Now see, I ran my program And it printed an exception as follows.

I used printStackTrace () in y program( The same above one.).


javac MyException.jav a -d .; java test.MyExceptio n 0
java.lang.Excep tion
at test.MyExceptio n.div(MyExcepti on.java:32)
at test.MyExceptio n.calculate(MyE xception.java:1 3)
at test.MyExceptio n.main(MyExcept ion.java:39)



What is the div specified here. my package name is test.

[pjerald]

I added a print statement after the catch part.

And i ran the program to cause an exception. Using division by zero.

It gave me an exception and also it printed the test print statement.

But i studied theoretically that if an exception caused, the jvm just throw an exception and exit the program. And how my print statement executed ?


See this,
javac MyException.jav a -d .; java test.MyExceptio n 0
java.lang.Excep tion
at test.MyExceptio n.div(MyExcepti on.java:32)
at test.MyExceptio n.calculate(MyE xception.java:1 3)
at test.MyExceptio n.main(MyExcept ion.java:39)
test :

test is my print statement.

[r035198x]

I added a print statement after the catch part.

And i ran the program to cause an exception. Using division by zero.

It gave me an exception and also it printed the test print statement.

But i studied theoretically that if an exception caused, the jvm just throw an exception and exit the program. And how my print statement executed ?


See this,
javac MyException.jav a -d .; java test.MyExceptio n 0
java.lang.Excep tion
at test.MyExceptio n.div(MyExcepti on.java:32)
at test.MyExceptio n.calculate(MyE xception.java:1 3)
at test.MyExceptio n.main(MyExcept ion.java:39)
test :

test is my print statement.

Perhaps it's time you have a look at at this?