constructor private ?

[samdeep aarzoo]

can we make constructor private
is it legal to make constructor private

[Richard Anderson]

Yes, you can make your contructor private; this is typically what you do when implementing the Singleton pattern.

Example:

public class MyClass {
private MyClass myInstance = null;

private MyClass() {
}

public static MyClass getInstance() {
if (myInstance == null) {
myInstance = new MyClass;
}

return myInstance;
}
}

And to use, put the following in your main method:

MyClass myClass = MyClass.getInstance();

Notice that you call getInstance() instead of "new MyClass()", which you wouldn't be able to do without a compiler error.

-Rich, SCJP

[fred rosenberger]

It is also used anytime you don't want anybody to be able to instantiate your class. Utility classes come to mind, like the Math class... all the useful methods are static, so you don't NEED to create an instance.

[Ilja Preuss]

Another pattern where it's used is the Typesafe Enum pattern, where the only instances are static final fields inside the class itself.