Java Reference
In-Depth Information
Listing 6-1.
The Simplest Thread in Java
// SimplestThread.java
package com.jdojo.threads;
public class SimplestThread {
public static void main(String[] args) {
// Creates a thread object
Thread simplestThread = new Thread();
// Starts the thread
simplestThread.start();
}
}
When you run the
SimplestThread
class, you do not see any output. The program will start and finish silently.
Even though you did not see any output, here are few things the JVM did when the two statements in the
main()
method were executed:
simplestThread.start()
, is executed, the JVM scheduled this
•
When the second statement,
thread for execution.
•
At some point in time, this thread got the CPU time and started executing. What code does a
thread in Java start executing when it gets the CPU time?
run()
method. You can define the
run()
method to be executed by a thread when you create an object of the
Thread
class. In your
case, you created an object of the
Thread
class using its default constructor. When you use
the default constructor of the
Thread
class to create its object (as in
new Thread()
), the
run()
method of the
Thread
class is called when the thread starts its execution. The following
sections in this chapter will explain how to define your own
run()
method for a thread.
•
A thread in Java always starts its execution in a
run()
method of the
Thread
class checks how the object of the
Thread
class was created.
If the thread object was created using the default constructor of the
Thread
class, it does not do
anything, and immediately returns. Therefore, in your program, when the thread got the CPU
time, it called the
run()
method of the
Thread
class, which did not execute any meaningful
code, and returned.
•
The
run()
method, the thread is dead, which means the
thread will not get the CPU time again.
•
When the CPU finishes executing the
Figure
6-4
depicts how the simplest thread example works.
