import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

/**
 * 
 * Instantiating Objects using Constructor Object.
 *
 */
public class ReflectionDemo
{
    public static void main(String[] args)
    {
        try
        {

            Class classObj = String.class;
            /*
             * Parameters:
             * 
             * parameterTypes - the parameter array
             * 
             * Returns: the Constructor object of the public
             * constructor that matches the specified parameterTypes
             * 
             */

            Constructor constructor = classObj.getConstructor(StringBuffer.class);
            StringBuffer sb = new StringBuffer("Peter");
            /*
             * Returns:a new object created by calling the constructor
             * this object represents
             */
            String str = (String) constructor.newInstance(sb);
            System.out.println(str);
        }
        catch (NoSuchMethodException | SecurityException
                | InstantiationException | IllegalAccessException
                | IllegalArgumentException
                | InvocationTargetException e)
        {
            e.printStackTrace();
        }

    }

}

Peter