初学者问题：是否一个java文件中，只能有一个public类？

[songq]

public class SimpleRunnable implements Runnable
{
public void run(){
System.out.println("Currently in Thread named'" + Thread.currentThread().getName()+"'");
}
}

public class ThreadTester
{
public static void main(String[] args){
SimpleRunnable aSR=new SimpleRunnable();
while(true){
Thread t=new Thread(aSR);
System.out.println("new Thread()"+(t==null?"fail":"succeed") +"ed.");
t.start();
try{
t.join();
}
catch(InterruptedException ignored){

}
}
}


以上是我的一个java文件，无论我将文件名为SimpleRunnable.java还是ThreadTester.java编译都会有以下错误：

---------- compile ----------
SimpleRunnable.java:8: class ThreadTester is public, should be declared in a file named ThreadTester.java
public class ThreadTester
^
1 error
Normal Termination
Output completed (15 sec consumed).

请指教.