How can I pass a parameter to a Java Thread?

Can anyone suggest to me how I can pass a parameter to a thread?

Also, how does it work for anonymous classes?

You need to pass the parameter in the constructor to the Runnable object:

public class MyRunnable implements Runnable {

   public MyRunnable(Object parameter) {
       // store parameter for later user
   }

   public void run() {
   }
}

and invoke it thus:

Runnable r = new MyRunnable(param_value);
new Thread(r).start();

For Anonymous classes:

In response to question edits here is how it works for Anonymous classes

   final X parameter = ...; // the final is important
   Thread t = new Thread(new Runnable() {
       p = parameter;
       public void run() { 
         ...
       };
   t.start();

Named classes:

You have a class that extends Thread (or implements Runnable) and a constructor with the parameters you'd like to pass. Then, when you create the new thread, you have to pass in the arguments, and then start the thread, something like this:

Thread t = new MyThread(args...);
t.start();

Runnable is a much better solution than Thread BTW. So I'd prefer:

   public class MyRunnable implements Runnable {
      private X parameter;
      public MyRunnable(X parameter) {
         this.parameter = parameter;
      }

      public void run() {
      }
   }
   Thread t = new Thread(new MyRunnable(parameter));
   t.start();

This answer is basically the same as this similar question: How to pass parameters to a Thread object

via constructor of a Runnable or Thread class

class MyThread extends Thread {

    private String to;

    public MyThread(String to) {
        this.to = to;
    }

    @Override
    public void run() {
        System.out.println("hello " + to);
    }
}

public static void main(String[] args) {
    new MyThread("world!").start();
}

This answer comes very late, but maybe someone will find it useful. It is about how to pass a parameter(s) to a Runnable without even declaring named class (handy for inliners):

    String someValue = "Just a demo, really...";

    new Thread(new Runnable() {
        private String myParam;

        public Runnable init(String myParam) {
            this.myParam = myParam;
            return this;
        }

        @Override
        public void run() {
            System.out.println("This is called from another thread.");
            System.out.println(this.myParam);
        }
    }.init(someValue)).start();

Of course you can postpone execution of start to some more convenient or appropriate moment. And it is up to you what will be the signature of init method (so it may take more and/or different arguments) and of course even its name, but basically you get an idea.

In fact there is also another way of passing a parameter to an anonymous class, with the use of the initializer blocks. Consider this:

    String someValue = "Another demo, no serious thing...";
    int anotherValue = 42;

    new Thread(new Runnable() {
        private String myParam;
        private int myOtherParam;
        // instance initializer
        {
            this.myParam = someValue;
            this.myOtherParam = anotherValue;
        }

        @Override
        public void run() {
            System.out.println("This comes from another thread.");
            System.out.println(this.myParam + ", " + this.myOtherParam);
        }
    }).start();

So all happens inside of the initializer block.

When you create a thread, you need an instance of Runnable. The easiest way to pass in a parameter would be to pass it in as an argument to the constructor:

public class MyRunnable implements Runnable {

    private volatile String myParam;

    public MyRunnable(String myParam){
        this.myParam = myParam;
        ...
    }

    public void run(){
        // do something with myParam here
        ...
    }

}

MyRunnable myRunnable = new myRunnable("Hello World");
new Thread(myRunnable).start();

If you then want to change the parameter while the thread is running, you can simply add a setter method to your runnable class:

public void setMyParam(String value){
    this.myParam = value;
}

Once you have this, you can change the value of the parameter by calling like this:

myRunnable.setMyParam("Goodbye World");

Of course, if you want to trigger an action when the parameter is changed, you will have to use locks, which makes things considerably more complex.