Restrict a class for creating second object in java

Question

Is there a way where we can restrict a class to create only a single object in java? It should give some exceptions if we try to create another new object. Example:

class A {}
public class Test {

    public static void main(String[] args) {

    A a1 =new A(); //This should be allowed
    A a2 =new A(); // This should not be allowed

    }
}

Answer 1

to try your additional requirement:

This should work, but I don't really see a point to it.

public class A {

  private static boolean instantiated;

  public A() throws Exception {
    if ( instantiated ) {
      throw new Exception("Already instantiated");
    }
    instantiated = true;
  }
}

Answer 2

You can use the special Singleton pattern. Most of the examples are on the internet.

    public class Singleton {
    private static Singleton instance;

    public static synchronized Singleton getInstance() {
        if (instance == null)
            instance = new Singleton();
        return instance;
    }
}