类类型引用 (Java)

我将立即显示代码，然后是问题：

class Callme{

    void call(String msg){
        System.out.print("[" + msg);
        try {
            Thread.sleep(100);
        }catch (InterruptedException e){
            System.out.println("Прервано!");
        }
        System.out.println("]");
    }
}

class Caller implements Runnable{

    String msg;
    Callme target;
    Thread t;

    public Caller (Callme targ, String s){

        target = targ;
        msg = s;

        t = new Thread(this);
        t.start();
    }

    public void run(){
        synchronized (target){
            target.call(msg);
        }
    }
}

public class Example {

    public static void main(String[] args) {

        Callme target = new Callme();

        Caller ob1 = new Caller(target, "Один");
        Caller ob2 = new Caller(target, "Два");
        Caller ob3 = new Caller(target, "Три");

        try {
            ob1.t.join();
            ob2.t.join();
            ob3.t.join();
        }catch (InterruptedException e){
            System.out.println("Прервано!");
        }
    }
}

我正在学习Java中的线程。面临对Caller类的一个元素的误解，即：Callme目标；它是对类类型的引用吗？它是如何工作的？为什么是她？为什么变量类型是Callme？我很困惑（