Thread Constructors

Chapter 3 - Creating and Starting a Thread Java Thread Programming Paul Hyde

size=1>  size=2>Copyright � 1999 Sams Publishing

size=4>Thread Constructors

size=2>The central constructor in face="Courier New" size=2>Thread face=Arial size=2> is

face="Courier New" size=2>public Thread(ThreadGroup group, Runnable target, String name)

size=2>The parameter size=2>name allows you to specify the name of the thread at construction time, rather than set it later using size=2>setName() size=2>.

size=2>The parameter size=2>target refers to an object of type size=2>Runnable. This object’s size=2>run() method will be invoked by the new thread instead of the color=#010100 face="Courier New" size=2>run() color=#010100 face=Arial size=2> method of color=#010100 face="Courier New" size=2>Thread color=#010100 face=Arial size=2>. Unlike a thread’s name, if you’re going to specify the size=2>target, you must do so at the time of construction. color=#008000 face=Arial size=2>Chapter 4 color=#000000 face=Arial size=2> explores in detail the issues involved in making a decision to use face="Courier New" size=2>Runnable face=Arial size=2> instead of extending face="Courier New" size=2>Thread face=Arial size=2>.

size=2>The parameter size=2>group lets you specify the size=2>ThreadGroup to which the new size=2>Thread will belong. Figure 3.1 shows the relationships among color=#010100 face="Courier New" size=2>Thread color=#010100 face=Arial size=2>s and face="Courier New" size=2>ThreadGroup face=Arial size=2>s.

size=2>

size=2>Figure 3.1: size=2>A sample hierarchy of ThreadGroups and Threads.

size=2>An analogy can be drawn between the file system concept of directories and files and the face="Courier New" size=2>ThreadGroup face=Arial size=2>/ size=2>Thread relationship. In a file system, a directory can contain files and other directories. These other directories, in turn, can contain other files and directories. Every file is in exactly one directory, which may itself be in another directory. Every directory except the one “root” or “base” directory is in another directory.

size=2>In Java, a size=2>ThreadGroup (much like a directory) can contain face="Courier New" size=2>Thread face=Arial size=2>s and other face="Courier New" size=2>ThreadGroup face=Arial size=2>s. These other face="Courier New" size=2>ThreadGroup face=Arial size=2>s can, in turn, contain other color=#010100 face="Courier New" size=2>Thread color=#010100 face=Arial size=2>s and face="Courier New" size=2>ThreadGroup face=Arial size=2>s. Every face="Courier New" size=2>Thread face=Arial size=2> (much like a file) is a member of a color=#010100 face="Courier New" size=2>ThreadGroup color=#010100 face=Arial size=2>, which may itself be a member of another size=2>ThreadGroup size=2>.

size=2>If a size=2>ThreadGroup is not specified at the time of a face="Courier New" size=2>Thread face=Arial size=2>’s construction, the face="Courier New" size=2>ThreadGroup face=Arial size=2> is inherited from the face="Courier New" size=2>Thread face=Arial size=2> that constructed it. color=#008000 face=Arial size=2>Chapter 10, “Thread Groups,” discusses size=2>ThreadGroups in more detail.

size=2>The size=2>Thread constructor used so far has been as follows:

face="Courier New" size=2>public Thread()

size=2>By default, the size=2>ThreadGroup is that of the size=2>Thread that constructs it. No external face="Courier New" size=2>Runnable face=Arial size=2> is specified, so the face="Courier New" size=2>Thread face=Arial size=2>’s own face="Courier New" size=2>run() size=2> method is called. Because no name is specified, the name of the size=2>Thread will be automatically generated as something such as color=#010100 face="Courier New" size=2>Thread-0 color=#010100 face=Arial size=2>.

size=2>The other constructors of face="Courier New" size=2>Thread face=Arial size=2> come somewhere in between the zero-argument constructor and the three-argument constructor. They specify some parameters of the three-argument constructor, and the nonspecified parameters take on their default values.

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