prevent constructors from being instantiating

[Gurpreet Singh]

can anyone suggest which is the right answer in this question and why? And if there are any other ways to prevent instantiating of constructors???

6. In regard to constructors, how can you prevent a class from being instantiated?

A. Use the private declaration.
B. Use anonymous classes.
C. Employ overloading.
D. Use only static inner classes.

[Richard Quist]

If the constructor is private then nothing outside of the class can access it...(any private method/field is invisible except to the class in which it is defined).

[Gurpreet Singh]

Please explain, why does
class Test {
public static void main(String[] args) {
Test t = new Test();
}
private Test() {
System.out.println("Constructor says that he is here.");
}
}

complies but

class Test {
public static void main(String[] args) {
Test t = new Test();
}
private Test() {
System.out.println("Constructor says that he is here.");
}
}

class MoreTest {
void test() {
Test t = new Test();
}
}

does not??? Maybe because the Instantiation is within the class itself (in the class in which the constructor is declared). Am I right???

[Richard Quist]

Exactly right. If it's private you can't access it UNLESS the access is made from the same class (as your first code example does).