How to call Private Constructor in Java

The method java.lang.Class.getDeclaredConstructor() can be used to obtain the constructor object for the private constructor of the class. The parameter for this method is a Class object array that contains the formal parameter types of the constructor.

A program that demonstrates this is given as follows −

Example

 Live Demo

package Test;
import java.lang.reflect.*;
public class Demo {
   String str;
   Double d;
   public Demo(String str, Double d) {
      this.str = str;
      this.d = d;
   }
   public static void main(String[] args) {
      try {
         Demo obj = new Demo("Apple", 55.983);
         Class c = obj.getClass();
         Class[] arguments = new Class[2];
         arguments[0] = String.class;
         arguments[1] = Double.class;
         Constructor constructor = c.getDeclaredConstructor(arguments);
         System.out.println("Constructor = " + constructor.toString());
      } catch(NoSuchMethodException e) {
         System.out.println(e.toString());
      } catch(SecurityException e) {
         System.out.println(e.toString());
      }
   }
}

output

Constructor = public Test.Demo(java.lang.String,java.lang.Double)

Now let us understand the above program.

An object of class Demo is created in the main() method. Then the array arguments[] stores the String.Class and Double.Class objects. Finally, the method getDeclaredConstructor() can be used to obtain the constructor object and this is displayed. A code snippet which demonstrates this is as follows −

Demo obj = new Demo("Apple", 55.983);
Class c = obj.getClass();
Class[] arguments = new Class[2];
arguments[0] = String.class;
arguments[1] = Double.class;
Constructor constructor = c.getDeclaredConstructor(arguments);
System.out.println("Constructor = " + constructor.toString());

Anvi Jain

Published on 09-Jan-2019 15:28:57