Packages
are the containers for the classes that are used to keep the class name space
compartmentalized. Packages are stored in a hierarchical manner and are
explicitly imported into new class definitions.
To create the packages use the “package”
command as follows:
package p1;
Here p1 is name of
the package and we insert the package p1 in the program with the import
statements as follows:
import p1;
Some packages
are
i)
import java.awt.*;
ii)
import java.awt.event.*;
iii)
import java.applet.*;
throw:
User can catching exceptions that
are thrown by the Java run – time system. However, it is possible for program
to throw an exception explicitly, using the throw statement. The general form
of throw is shown here:
throw ThrowableInstance;
Here,
ThrowableInstance must be an object of type Throwable or a subclass of
Throwable. There is two ways obtain a Throwable object: using a parameter into
a catch clause, or creating one with the new operator.
The flow of execution stops
immediately after the throw statement; any subsequent statements are not executed.
Class bug extends Exception
{
………//statement
}
……
…….
int
i=10;
try
{
if(i<12) throw
new OutOfRange();
}catch(OutOfRange e)
{
…….//statement
}
throws:
If a method is
capable of causing an exception that it does not handle, it must specify this
behavior so that callers of the method can guard themselves against that
exception. We do this by including a throws clause in the method declaration. A
throw clause lists the types of exception that a method might throw. This is necessary
for all exception, except those of type Error or RuntimeException or any of
their subclasses. All other exceptions that a method can throw must be declared
in the throws clause. If they are not, a compile – time error will result.
type method – name (parameter list)
throws exception list
{
// body of the mewthod
}
