Java Class getDeclaredConstructor() Method

The getDeclaredConstructoe() method of java Class class returns a constructor object representing all the constructors present in the class.

Syntax

public Constructor<T> getDeclaredConstructor(Class<?>... parameterTypes)
  throws NoSuchMethodException,   SecurityException

Parameter

parameterTypes - the parameter array

Returns

Constructor object.

Throws

NoSuchMethodException , SecurityException

Example 1

import java.lang.reflect.Constructor;
public class ClassgetDeclaredConstructorExample1  {

    public ClassgetDeclaredConstructorExample1() {
    }

    public ClassgetDeclaredConstructorExample1(int i) {
    }

    private ClassgetDeclaredConstructorExample1(String str) {
    }

    public static void main(String... args) throws NoSuchMethodException {
        Class<ClassgetDeclaredConstructorExample1> cls = ClassgetDeclaredConstructorExample1.class;
        Constructor<ClassgetDeclaredConstructorExample1> constrct = cls.getDeclaredConstructor();
        System.out.println("Constructor with no parameter :  " +constrct);

        constrct = cls.getDeclaredConstructor(int.class);
        System.out.println("Constructor with int as parameter type  :  " +constrct);

        constrct = cls.getDeclaredConstructor(String.class);
        System.out.println("Constructor with String as  parameter  type  :  "  +constrct);
    }

}

Test it Now

Output:

Constructor with no parameter :  public ClassgetDeclaredConstructorExample1()
Constructor with int as parameter type  :  public ClassgetDeclaredConstructorExample1(int)
Constructor with String as  parameter  type  :  private ClassgetDeclaredConstructorExample1(java.lang.String)

Example 2

//import statements...
import java.lang.reflect.*;

public class ClassgetDeclaredConstructorExample2 {

   public static void main(String[] args) {
    
      try {
         ClassgetDeclaredConstructorExample2  obj  = new ClassgetDeclaredConstructorExample2();
         Class cls = obj.getClass();
        //creating rray of type class
         Class[]  arr = new Class[2];
         arr[0] = Double.class;
         arr[1] = Long.class;
         Constructor cnstrct = cls.getDeclaredConstructor(arr);
         System.out.println("Constructor  =  " + cnstrct.toString());
      } catch(NoSuchMethodException e) {
         System.out.println(e.toString());  //print exception object e
      } catch(SecurityException e) {
         System.out.println(e.toString());  //print exception object e
      }
   }

   private ClassgetDeclaredConstructorExample2()  {
      System.out.println("Default constructor");
   }

   public ClassgetDeclaredConstructorExample2(Double dbl, Long lng) {
       this.dbl = dbl;
       this.lng = lng;
   }

   Double dbl = new Double(3.9d);
   Long lng = new Long(7687);
} 

Test it Now

Output:

Default constructor
Constructor  =  public ClassgetDeclaredConstructorExample2(java.lang.Double,java.lang.Long)

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