asked on

How do I declare and instantiate a new class object, but with a String name reference instead?

I have a 'controller' class. From my main() in the 'entry' class, I call the controller class "ThreadInit" to declare and instantiate one of 4 class objects, so I need to make this generic, accepting a String classname to instantiate, to then start new threads...

Here's my controller class...

import java.lang.Thread;

public class ThreadInit implements Runnable{
            private Thread t;
            private String threadName;
            private DButil obj = null; //gets the database object

            public ThreadInit(String className) {
                  threadName = className;
            }

            public void start() {
                  if (t == null){
                        t = new Thread(this, threadName);
                        t.start();
                  }
            }

            @Override
            public void run() {
                  process();
            }

            private void process() {
                  this.obj = new DButil();
                  if (obj.getConn() != null) {
                        //MPhead mphead1 = new MPhead(obj);

// It is here, I want to make this more generic to handle any classname and instantiate // ... it, to further start a thread
                        Class classObj = new Class.forName(threadName);

                        //logger.appendLog(mphead1.getLog().toString());

                  } else {
                        logger.appendLog(" No Connection");
                  }
            }
      }

What is the best method to do this? Thank you!

CEHJ

Rather than using reflection, you can also use a Factory pattern, since you only have a few possible different types

m3developer2

ASKER

Can you give me a code sample using 'threadName' as the class name reference to instantiate?

CEHJ

I think there's some confusion here.

 t = new Thread(this, threadName);
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The second parameter can only ever be a String anyway, so it don't see how that applies to a 'new class object' ..?

m3developer2

ASKER

Let me try a different example. I have a controller class named 'start', with the main() method, and some 'thread' classes. The controller class should : 1) Iterate an String array of class Names, 2) Instantiate each 'thread' class as an object, 3) Invoke it's run() method. The objective is that each 'thread' class is a database call, since queries are unknown runtimes, each will be in it's own thread.

Can I get an example of code to dynamically declare/instantiate the class names in 'start'
Here are the classes...

Controller:

package model;


public class start {

	public static void main(String[] args) {
		String[] classNames = new String[]{"model.Thread1","model.Thread2"};
		
		startThreads(classNames);
		 
	}
	
	
	public static void  startThreads(String[] classNames) {
	
		for (int i = 0; i < classNames.length; i++) {
		
			try {
				// Instantiate an object using the String className at index i
				Class cl = Class.forName(classNames[i].toString());
				
				// invoke the run() method of the current instantiated class here, starting it as a thread...
				
				
			} catch (ClassNotFoundException e) {
				e.printStackTrace();
			}
		}
	}
}

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Thread classes

public class Thread1 implements Runnable{
	
	public Thread1() {

	}

	@Override
	public void run() {
		// GO run a query and do something with it, take all the time it requires...
		System.out.println("Starting Thread1...");
		
	}
}



public class Thread2 implements Runnable{

	@Override
	public void run() {
		System.out.println("Starting thread2");
		
	}
}

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CEHJ

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m3developer2

ASKER

Thank you CEHJ, although, I can't seem to find the jar for the foreign classes at that link....
I signed up, just dont see the download...

Thank you!

m3developer2

ASKER

Nevermind!, I just found the link in the word 'Help'...

Thanks, I'll try this, this site is great for other challenges...

CEHJ

I signed up, just dont see the download...

I think i need to make it more obvious