Malformed URL Exception

[Pallavi Chakraborty]

Hello everybody,
I have the following program which catches a MalformedURLException. The value of the string variable URL is initialized to null.
Instead of this, can I get the URL as an input from the user and then check to see if it is in the URL format.
I am not sure how this would be done.
Here is the code

  
import javax.swing.JOptionPane;

class MalformedURLException extends Exception { 
    MalformedURLException(String msg)
{
 super(msg); 
}
}
public class ThrowEx
{
public void urltest()
{

try
{
String url = null;
if(url == null) { throw new MalformedURLException("test"); 


}

}
catch (MalformedURLException e)
{
System.out.println("Dealt with: " + e);
}


}

public static void main(String args[])
{
new ThrowEx().urltest();
System.out.println("returning from main");
}
}
Thanks in advance
Pallavi

[Barry Gaunt]

Can you not jast pass the string from the user to the java.net.URL constructor? The constructor throws a MalformedURLException if it cannot parse the string.

[Pallavi Chakraborty]

Let me try that,
Pallavi

[Pallavi Chakraborty]

Hello Barry,
I tried adding the constructor of java.net.URL
I am pasting the modified code.

import javax.swing.JOptionPane;
//I added this piece of code to import java.net.URL;
import java.net.URL;
class MalformedURLException extends Exception { 
    MalformedURLException(String msg)
{
 super(msg); 
}
}

public class ThrowEx 
{
public void urltest()
{

  
String url = JOptionPane.showInputDialog("Enter an URL");
  try
{

// I added this code which creates an object of the class URL passing a string as a parameter.
URL u  = new URL(url) throw new MalformedURLException("test"); 



}
catch (MalformedURLException e)
{
System.out.println("Dealt with: " + e);
}


}

public static void main(String args[])
{
new ThrowEx().urltest();
System.out.println("returning from main");
}
}

However, I get this error:
[CODE}
C:\JCreator LE\MyProjects\Test1\Ex5.7\ThrowEx.java:22: ';' expected
URL u = new URL(url) throw new MalformedURLException("test");
^
[/CODE]
Thank you
Pallavi

[Jim Yingst]

Well, look at the line the compiler shows you:

URL u = new URL(url) throw new MalformedURLException("test");
Does this line make any sense? What exactly is it supposed to do?

[Pallavi Chakraborty]

Hi Jim,
This line is supposed to create an object of class URL and send a string object into its constructor.If the string specifies an unknown protocol, then an exception will be thrown.
I know to catch the Malformed URL exception, it has to reported somewhere. I had tried moving the throw statement to the method urltest and making it a throws statement.
I think I am missing a very simple point.
I just don't know what.
Thanks
Pallavi

[Jim Yingst]

When you describe what you want the code to do, you used the word "if". Look again at the line of code. There's no "if". It looks as though two different statements have been combined without any puctuation.

[Pallavi Chakraborty]

Hello Jim,

The if statement is for an unknown protocol.
I tried the follwong code but I am still not clear.

try
{

// I added this code which creates an object of the class URL passing a string as a parameter.

URL u  = new URL(url);
if(u == null)

throw new MalformedURLException("test");

else

System.out.print(u);



}
catch (MalformedURLException e)
{
System.out.println("Dealt with: " + e);
}

The if part , how do we specify the unknown protocol.
The only thing I could think of is the URL being a null.
I appreciste your patience on this.
Thank you
Pallavi

[Pallavi Chakraborty]

Hello Jim,
I worked on it a little more and came up with this:

 
public void urltest() 
{
  String url = JOptionPane.showInputDialog("Enter an URL");
  MalformedURLException oops = null;
  URL u =null;
  
  if(!(url == null))
  {
  try
  {
  
u = new URL(url);
System.out.print(u);
} 

catch(MalformedURLException e)
{
System.out.print("Dealt with:" + e);
}
}

 

However I get these two errors:
C:\Pallavi's\Javah\JCreator LE\MyProjects\Test1\Ex5.7\ThrowEx.java:27: unreported exception java.net.MalformedURLException; must be caught or declared to be thrown
u = new URL(url);
^
C:\Pallavi's\Javah\JCreator LE\MyProjects\Test1\Ex5.7\ThrowEx.java:30: exception MalformedURLException is never thrown in body of corresponding try statement
catch(MalformedURLException e)
^
2 errors
Process completed.
Thanks
Pallavi

[Pallavi Chakraborty]

Hello Jim,
I tried again and this code compiles without error:

 
import javax.swing.JOptionPane;
//I added this piece of code to import java.net.URL;
import java.net.MalformedURLException;
import java.net.URL;
//class MalformedURLException extends Exception { 
  //  MalformedURLException(String msg)
//{
// super(msg); 
//}
//}

public class ThrowEx 
{
public void urltest() 
{
  String url = JOptionPane.showInputDialog("Enter an URL");
  MalformedURLException oops = null;
  URL u;
  
  if(!(url == null))
  {
  try
  {
  
u = new URL(url);
System.out.print(u);
} 

catch(MalformedURLException e)
{
System.out.print("Dealt with:" + e);
}
}



}
public static void main(String args[]) 
{

new ThrowEx().urltest();

System.out.println("returning from main");
}
}

What do you think ?
Pallavi