Java.lang.Class.getDeclaredConstructor() Method

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Description

The java.lang.Class.getDeclaredConstructor() method returns a Constructor object that reflects the specified constructor of the class or interface represented by this Class object. The parameterTypes parameter is an array of Class objects that identify the constructor's formal parameter types, in declared order.

Declaration

Following is the declaration for java.lang.Class.getDeclaredConstructor() method

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

Parameters

parameterTypes − This is the parameter array.

Return Value

This method returns the Constructor object for the constructor with the specified parameter list.

Exception

• NoSuchMethodException − If a matching method is not found.

• SecurityException − If a security manager, s, is present.

Example

The following example shows the usage of java.lang.Class.getDeclaredConstructor() method.

package com.tutorialspoint;

import java.lang.reflect.*;

public class ClassDemo {

   public static void main(String[] args) {
    
      try {
         ClassDemo cls = new ClassDemo();
         Class c = cls.getClass();

         // constructor with arguments as Double and Long
         Class[] cArg = new Class[2];
         cArg[0] = Double.class;
         cArg[1] = Long.class;
         Constructor ct = c.getDeclaredConstructor(cArg);
         System.out.println("Constructor = " + ct.toString());
      } catch(NoSuchMethodException e) {
         System.out.println(e.toString());
      } catch(SecurityException e) {
         System.out.println(e.toString());
      }
   }

   private ClassDemo() {
      System.out.println("no argument constructor");
   }

   public ClassDemo(Double d, Long l) {
      this.d = d;
      this.l = l;
   }

   Double d = new Double(3.9d);
   Long l = new Long(7687);
} 

Let us compile and run the above program, this will produce the following result −

no argument constructor
Constructor = public ClassDemo(java.lang.Double,java.lang.Long)