Exception

[sreelakshmi sarma]

import java.io.*;
class testexception
{
public void some() throws IOException
{
System.out.println("some");
}
public void some2() throws FileNotFoundException
{
some();
System.out.println("some2");
}

public void some3()
{
try
{
some2();
}
catch(IOException e)
{
System.out.println("i got you");
}
}
public static void main(String args[])
{
testexception te1 = new testexception();
te1.some3();
}
}
It's giving me a compile time error that IoException must be declared or it must be caught. But i am catching IOException in the some3. Could somebody please explain this to me.
Thanks.

[maha anna]

Sree,Use the [ CODE ] [ /CODE ] tags when you post your code.
The compile error is because of this code.
<pre>
public void some() throws IOException{
System.out.println("some");
}
public void some2() throws FileNotFoundException {
// either this shd be changed to IOException or the foll. some();
method invocation MUST be enclosed with try..catch(IOException)
some();
System.out.println("some2");
}
</pre>
regds
maha anna

[This message has been edited by maha anna (edited March 09, 2000).]

[Manju Swamy]

Exception hierarchy
<PRE>
+--java.lang.Exception
|
+--java.io.IOException
|
+--java.io.FileNotFoundException
</PRE>
Here are some of the possible choices:
1. You can enclose the call to some() method in try ... catch block.

import java.io.*;
class TestException {
public void some() throws IOException {
System.out.println("some");
}
public void some2() throws FileNotFoundException {
[B]try {[/B]
some();
[B]} catch (IOException e) {
System.out.println("i got you some()");
}[/B]
System.out.println("some2");
}
public void some3(){
try {
some2();
} catch (IOException e) {
System.out.println("i got you");
}
}
public static void main(String args[]) {
TestException te1 = new TestException();
te1.some3();
}
}

2. Change the some2() method declaration to throw IOException inaddtion to FileNotFoundException.

import java.io.*;
class TestException {
public void some() throws IOException {
System.out.println("some");
}
public void some2() throws FileNotFoundException, [B]IOException[/B] {
some();
System.out.println("some2");
}
public void some3(){
try {
some2();
} catch (IOException e) {
System.out.println("i got you");
}
}
public static void main(String args[]) {
TestException te1 = new TestException();
te1.some3();
}
}

3. Change the some2() method declaration to throw IOException only, since it is parent class of FileNotFoundException.

import java.io.*;
class TestException {
public void some() throws IOException {
System.out.println("some");
}
public void some2() throws [B]IOException[/B] {
some();
System.out.println("some2");
}
public void some3(){
try {
some2();
} catch (IOException e) {
System.out.println("i got you");
}
}
public static void main(String args[]) {
TestException te1 = new TestException();
te1.some3();
}
}

Hope this helps.

[sreelakshmi sarma]

Thank you very much Manju & Maha.

[sreelakshmi sarma]

One small question though. I think i read somewhere that "throws" and "try & catch" cannot be put together. Can someone clarify this to me.

[maha anna]

throws is different from throw keyword.
1. 'throw' may/may not have try..catch statements
<pre>
ex. void m1() throws IOException{ throw new IOException(); }
ex. void m2() { throw new UnknownError(); }
ex. void m3() {
try {
throw new IOException();
}catch( IOException e) {}
}
2.'throws' comes in method and constructor declarations
ex. void m1() throws IOException {
throw new IOException();
}
ex. test() throws Exception { //constructor throwing exception
}
</pre>
regds
maha anna

[This message has been edited by maha anna (edited March 09, 2000).]

[sreelakshmi sarma]

Maha Anna i don't understand your point.I know that "throw" and "throws" are two different keywords. I am not confused about that. My question is can "try & catch" and "throws" be put together.Please take a look at the following code.
CODE:
import java.io.*;
class TestException {
public void some() throws IOException {
System.out.println("some");
}
public void some2() throws FileNotFoundException {
try {
some();
} catch (IOException e) {
System.out.println("i got you some()");
}
System.out.println("some2");
}
}
I hope i making sense now.
Thanks.

[maha anna]

Yes. You can use both in a method/constructor.
regds
maha anna

[sreelakshmi sarma]

Thanks Anna.

[Naruki]

I thought that you couldn't use "throws" if the try{...} catch{...} block caught the same exception, unless you rethrew it.
Apparently I was wrong. Here's some very simple code to illustrate:

<FONT color=blue>import</FONT> java.io.*;
<FONT color=blue>class</FONT> TestException <FONT color=red>{</FONT>
    <FONT color=blue>public void</FONT> some<FONT color=red>()</FONT> <FONT color=blue>throws</FONT> <FONT color="#000080">IOException</FONT> <FONT color=red>{</FONT>
        <FONT color=blue>try</FONT> <FONT color=red>{</FONT>
            <FONT color=blue>throw new</FONT> <FONT color="#000080">IOException</FONT><FONT color=red>()</FONT>;
        <FONT color=red>}</FONT>
        <FONT color=blue>catch</FONT> <FONT color=red>(</FONT><FONT color="#000080">IOException</FONT> e<FONT color=red>)</FONT> <FONT color=red>{</FONT>
            <FONT color=green>/* do nothing */</FONT>
        <FONT color=red>}</FONT>
        <FONT color="#000080">System</FONT>.out.println(<FONT color=cyan>"some() worked!"</FONT>);
    <FONT color=red>}</FONT>
    <FONT color=blue>public static void</FONT> main<FONT color=red>(</FONT>String args<FONT color=red>[]) {</FONT>
        TestException t = <FONT color=blue>new</FONT> TestException<FONT color=red>()</FONT>;
        <FONT color=blue>try</FONT> <FONT color=red>{</FONT>
            t.some<FONT color=red>()</FONT>;
        <FONT color=red>}</FONT>
        <FONT color=blue>catch</FONT> <FONT color=red>(</FONT><FONT color="#000080">IOException</FONT> e<FONT color=red>) {</FONT>
            <FONT color="#000080">System</FONT>.out.println(<FONT color=cyan>"I caught you some()"</FONT><FONT color=red>)</FONT>;
        <FONT color=red>}</FONT>
    <FONT color=red>}</FONT>
<FONT color=red>}</FONT>

[This message has been edited by Naruki (edited November 01, 2001).]