throws & throw ??

[dlc]

How to distinguish the practical urage between [throws] and [throw]?
And in what way can they be applied to?
thanks a lot

  
class ColorException extends Exception {}
class WhiteException extends ColorException {}
class White {
void m1() throws ColorException {throw new
WhiteException();}
void m2() throws WhiteException {}
public static void main (String[] args) {
White white = new White();
int a,b,d,f;
a = b = d = f = 0;
try {white.m1();a++;} catch (ColorException e)
{b++;}
try {white.m2();d++;} catch (WhiteException e)
{f++;}
System.out.print(a+","+b+","+d+","+f);
}
}

A:0,1,1,0 BUT,WHY???

[David Peterson]

It will help you a lot to understand the code if you format it neatly with proper indentation...

class ColorException extends Exception
{
}
class WhiteException extends ColorException
{
}
class White {
    void m1() throws ColorException
    {
        throw new WhiteException();
    }
    
    void m2() throws WhiteException
    {
    }
    
    public static void main (String[] args)
    {
        White white = new White();
        int a,b,d,f;
        a = b = d = f = 0;
        try
        {
            white.m1();
            a++;
        }
        catch (ColorException e)
        {
            b++;
        }
        
        try
        {
            white.m2();
            d++;
        }
        catch (WhiteException e)
        {
            f++;
        }
        
        System.out.print(a+","+b+","+d+","+f);
    }
}

You can now see that the throws clause is part of the method declaration, whereas the throw statement is part of the method body.

void m1() throws ColorException
{
    throw new WhiteException();
}

The throws clause tells you what exceptions the method may throw. The person calling the method must either handle these exceptions (with a try..catch) or declare them in its own throws clause (which will pass the exception up the call-stack until something handles it, or the application crashes).
The throw statement actually throws an exception.
[ May 09, 2004: Message edited by: David Peterson ]

[Dirk Schreckmann]

dlc,
Welcome to JavaRanch!
We ain't got many rules 'round these parts, but we do got one. Please change your display name to comply with The JavaRanch Naming Policy.
Thanks Pardner! Hope to see you 'round the Ranch!