How can I access a private constructor of a class?

Question

I am a Java developer. In an interview I was asked a question about private constructors:

Can you access a private constructor of a class and instantiate it?

I answered 'No' but was wrong.

Can you explain why I was wrong and give an example of instantiating an object with a private constructor?

Answer 1

One way to bypass the restriction is to use reflections:

import java.lang.reflect.Constructor;  public class Example {     public static void main(final String[] args) throws Exception {         Constructor<Foo> constructor = Foo.class.getDeclaredConstructor();         constructor.setAccessible(true);         Foo foo = constructor.newInstance();         System.out.println(foo);     } }  class Foo {     private Foo() {         // private!     }      @Override     public String toString() {         return "I'm a Foo and I'm alright!";     } } 

Answer 2

• You can access it within the class itself (e.g. in a public static factory method)
• If it's a nested class, you can access it from the enclosing class
• Subject to appropriate permissions, you can access it with reflection

It's not really clear if any of these apply though - can you give more information?