How to create com.ms.lang.Delegate in J#

Article
11/23/2005

Creating com.ms.lang.Delegate in J#

Single-cast Delegate

Single-cast Delegate derived from com.ms.lang.Delegate calls only one function. This delegate type represents objects that cannot be chained together in an invocation list.

The Syntax for the single-cast delegate is shown below:

delegate int TestDelegate (int a, int b);

As you can see, the “delegate” keyword is used to declare a Single cast delegate derived from com.ms.lang.Delegate. When compiler encounters the above statement, it will create a new class called TestDelegate which as said, would have been derived from com.ms.lang.Delegate.

Since, this type of Delegate cannot be combined, hence combining it with any other delegate will throw an exception saying:

com.ms.lang.MulticastNotSupportedException: class check does not support multicasting

For example, following program would throw an exception as mentioned as above:

import com.ms.lang.*;

delegate void check(int a, int b);

public class test

{

public void greater(int a, int b)

{

if (a > b)

System.out.println("Greater");

else

System.out.println("Small");

}

public void lower( int a, int b)

{

return;

}

public static void main(String args[])

{

test t = new test();

check ch = new check(t, "greater");

check ch1 = new check(t, "lower");

Delegate.combine(ch, ch1);

}

Multicast Delegates

Multicast Delegates derived from com.ms.lang.Delegates can be a part of the link list and always points to the head of the link list. The Syntax for the single-cast delegate is shown below:

multicast delegate void TestDelegate (int a, int b);

As you can see “multicast” keyword along with “delegate” keyword is used while declaring a multicast delegate in J#. The return type of this muticast delegate cannot be anything else than void else VJ# compiler: vjc compiler would throw an error.

It needs to be noted that only delegates which are of the same type (i.e. which belongs to the same class) can be combined. You can also not combine a mutlicast and a single-cast delegate. For example, the following program would an exception saying:

java.lang.IllegalArgumentException: cannot combine Delegates of different types

import com.ms.lang.*;

multicast delegate void multi_check(int a, int b);

delegate void single_check(int a, int b);