abstract classes with private constructor

[Maneeesh Saxena]

higreat Ranchers,
please tell me what is the utility of abstract classes having private constructor.

thanks in advance

[Vaibhav Chauhan]

We can have static method inside which we can invoke the private constructor hence we can create the instance directly by invoking static method.

[Aniket Patil]

We can have static method inside which we can invoke the private constructor hence we can create the instance directly by invoking static method.

You mean this?

  public abstract class TestConstructor
{
private TestConstructor()
{
}
 
public static void makeObject()
{
new TestConstructor();
}

public static void main(String[] args)
{
makeObject();
}
}  

javac TestConstructor.java
TestConstructor.java:9: TestConstructor is abstract; cannot be instantiated
new TestConstructor();
^
1 error

A class type should be declared abstract only if the intent is that subclasses can be created to complete the implementation. If the intent is simply to prevent instantiation of a class, the proper way to express this is to declare a constructor of no arguments, make it private, never invoke it, and declare no other constructors. A class of this form usually contains class methods and variables.

A compile-time error occurs if an attempt is made to create an instance of an abstract class using a class instance creation expression

[ December 28, 2006: Message edited by: Aniket Patil ]

[Steven.xu xu]

I don't see the point. Since it is abstract, it must be inherited by a subclass while its constractor is private which prevent its subclass from instantiation. Looks for me it is a useless class.

[Vaibhav Chauhan]

oops !!! I didn't look at abstract word.... the solution that i proposed is for non abstract class...

[Ramya Chowdary]

If it is a useless class, why Java compiler not complaining about this?