JAVA help!!!!!!!!!!!!!!?

Question

im confused with instantiable and non-instantiable classes.. please give me some examples so that i can fully understand their differences

Answer 1

class are templates right? when you instantiate it, it becomes an object. only CONCRETE classes can be instantiable though.. the perfect example of a non-instantiable class is an abstract class because it's not concrete, here's an example

abstract class Human{
public abstract void walk();
public abstract void run();
pulbic abstract void sleep();
}

a class like this can never be instantiated, only when you have a concrete class will you be able to use it.. a concrete class example:

class Guy extends Human{
public void walk(){
System.out.println("Guy walking");
}
public void run(){
System.out.println("Guy running");
}
pulbic void sleep(){
System.out.println("zzZZzzzz");
}
}

a test sample:
class test{
public static void main(String args[]){
Human h = new Human();// <-- this will be an error
Guy g = new Guy(); // this is legal
g.walk();
g.run();
g.sleep();
}
}

hope it clears your mind

Answer 2

KewlyBug provided one kind of example: abstract classes. But you can also have concrete classes that cannot be instantiated. The java.lang.System class is an example. There are no public constructors, so you cannot call System sys = new System(), for example. All of the System methods are static, and since System represents your current system, which there can only be one of at a time, it makes sense that you are not allowed to make multiple instances.

Answer 3

An object is an instance of a class.

A class is a template.

There are some classes that are part of the standard Java library that are not meant to be an object. So, they make them noninstantiable.

Answer 4

http://www.vivarem.com/files/IN/gn/916/ covers both abstract classes and interfaces in java