Instantiate a class object with constructor that accepts a string parameter?

user_430276 0
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I would like to instantiate an object from its Class object, using the constructor that accepts a single String argument.

Here is some code that approaches what I want: 

Object object = null;
Class classDefinition = Class.forName("javax.swing.JLabel");
object = classDefinition.newInstance();

However, it instantiates the JLabel object with no text. I would like to use the JLabel constructor that accepts a string as the initial text. Is there a way to select a specific constructor from a Class object?

reflection constructor html java
4 Answers

Some times it's not necessary to create object for the class to call is constructors and methods. You can call methods of class without creating direct object. It's very easy to call a constructor with parameter.

import java.lang.reflect.*;
import java.util.*;

class RunDemo
{
    public RunDemo(String s)
    {
        System.out.println("Hello, I'm a constructor. Welcome, "+s);
    }  
    static void show()
    {
        System.out.println("Hello.");
    }
}
class Democlass
{
    public static void main(String args[])throws Exception
    {
        Class.forName("RunDemo");
        Constructor c = RunDemo.class.getConstructor(String.class);  
        RunDemo d = (RunDemo)c.newInstance("User");
        d.show();
    }
}

the output will be:

Hello, I'm a constructor. Welcome, User

Hello.

Class.forName("RunDemo"); will load the RunDemo Class.

Constructor c=RunDemo.class.getConstructor(String.class); getConstructor() method of Constructor class will return the constructor which having String as Argument and its reference is stored in object 'c' of Constructor class.

RunDemo d=(RunDemo)c.newInstance("User"); the method newInstance() of Constructor class will instantiate the RundDemo class and return the Generic version of object and it is converted into RunDemo type by using Type casting.

The object 'd' of RunDemo holds the reference returned by the newInstance() method.

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