HELP ! ! ! something simple . . . :D

Hello all . . .

I need a help for something simple.

I have create two php classes

for example

class classname_1
{

}

and the

class classname_2
{

}

if i like to make an instance of class classname_1 into the classname_2
how can i do it ? ? ?

I have try to make one like

class classname_2
{
$obj_class1 = new classname_2();
}

but it doesn't work ! ! ! !

Why ? ? ?

Thanks a lot . . . :D

.