Java Fundamentals 22

1 Overview of multi-Threading 1.1 processes

• Is the program that is running. The system is a separate unit for resource allocation and scheduling. Each process has its own memory space and system resources.

What is the meaning of more than 1.2 processes?

• A single-process computer can do only one thing, and we now have a computer to do multiple things. For example: Play the game while listening to music.
• Today's computers support multiple processes, can perform multiple tasks in a single time period, and can increase CPU usage.

1.3 Threads

• Multiple tasks can be performed within a process, and each of these tasks can be viewed as a thread.
• A thread is the execution unit (execution path) of a process.
• Single thread: If the program has an execution path.
• Multithreading: If the program has more than one execution path.

1.4 What is the meaning of multi-threading?

• Multithreading exists, not to improve the execution speed of the program. In fact, to improve application usage.
• The implementation of the program is actually in the grab CPU resources, that is, the CPU execution right.
• Multiple processes are robbing this resource, and one of those processes has a higher chance of grabbing CPU execution if the execution path is more.
• The execution of a thread is random.

1.5 How Java programs work

• The Java command launches the Java Virtual machine and starts the JVM, which is equivalent to initiating a process. The process automatically starts a main thread and then calls the main method of a class by the main thread, so the main method runs in the main thread.
• The JVM startup starts at least the garbage collection thread and the main thread, so it is multithreaded.

2 Multi-Threading Implementation Scenario 2.1 Multi-Threading implementation Scenario One

• Steps:
• ① create a class to inherit the thread class.
• ② the subclass to rewrite the run () method.
• ③ the object that created the subclass.
• ④ Start Thread

• Example:

 PackageCom.xuweiwei;/*** Multithreading implementation: * Because threads are dependent on processes, we should create a process first. * and the process is created by the system, so we should call the system function to create a process. * Java is not directly with the system function, so we have no way to directly implement multithreaded programs. * However, Java can be called C or C + + written programs to implement multithreaded programs. * from C or C + + to invoke the system function creation process, then by Java to invoke such things, and then provide some APIs for us to use. In this way, we can implement multithreaded programs. */ Public classMyThreadextendsThread {@Override Public voidrun () { for(inti = 0; I < 10; i++) {System.out.println (Thread.CurrentThread (). GetName ()+"= " +i); }    }}

 Package Com.xuweiwei;  Public class mythreadtest {    publicstaticvoid  main (string[] args) {          New  MyThread ();        T1.start ();         New MyThread ();        T2.start ();    }}

2.2 Gets the name of the thread object and sets the name of the thread object

• Method: Returns the name of the thread

 Public Final String GetName ()

• Method: Set the name of the thread

 Public Final void setName (String name)

• Method: Returns a reference to the currently executing thread object

 Public Static Thread CurrentThread ()

• Example: Non-parametric construction method +setname

 package   Com.xuweiwei;  public  class   MyThread extends   public   run () { for  (int  i = 0; i < i++) {Sy        Stem.out.println (Thread.CurrentThread (). GetName ()  + "=" + i); }    }}

 Package Com.xuweiwei;  Public class mythreadtest {    publicstaticvoid  main (string[] args) {          New  MyThread ();         New MyThread ();         // Set the name        of the thread T1.setname ("T1");        T2.setname ("T2");        T1.start ();        T2.start ();    }}

• Example: A method for constructing a parameter

 PackageCom.xuweiwei; Public classMyThreadextendsThread { PublicMyThread () {} PublicMyThread (String name) {Super(name); } @Override Public voidrun () { for(inti = 0; I < 10; i++) {System.out.println (Thread.CurrentThread (). GetName ()+"= " +i); }    }}

 Package Com.xuweiwei;  Public class mythreadtest {    publicstaticvoid  main (string[] args) {          New MyThread ("T1");         New MyThread ("T2");        T1.start ();        T2.start ();    }}

• Example: Get the name of the thread object where the Main method resides

 Package Com.xuweiwei;  Public class mythreadtest {    publicstaticvoid  main (string[] args) {        System.out.println (Thread.CurrentThread (). GetName ());}    }

2.3 Control of the thread

• Method: Thread Sleep

 Public Static void sleep (long Millis)  throws interruptedexception

• Method: Join thread, wait for the thread to terminate

 Public Final void throws Interruptedexception

• Method: Thread comity pauses the current executing thread object and executes other threads.

 Public Static void yield ()

• Method: Daemon Thread

 Public Final void Setdaemon (boolean on)

• Method: Middle Thread thread

 Public void Interrupt ()

• Example:

 PackageCom.xuweiwei; Public classMyThreadextendsThread {@Override Public voidrun () { for(inti = 0; I < 10; i++) {            Try{Thread.Sleep (1000); } Catch(interruptedexception e) {e.printstacktrace (); } System.out.println (Thread.CurrentThread (). GetName ()+"= " +i); }    }}

• Example:

 Package Com.xuweiwei;  Public class extends Thread {    @Override    publicvoid  run () {        for (int i = 0; I < 100; i++) {            + "=" + i);     }}}

 PackageCom.xuweiwei; Public classMythreadtest { Public Static voidMain (string[] args) {MyThread T1=NewMyThread (); MyThread T2=NewMyThread (); MyThread T3=NewMyThread (); T1.setname ("Liyuan"); T2.setname ("Li Jiancheng"); T3.setname ("Li Shimin");        T1.start (); Try{t1.join (); } Catch(interruptedexception e) {e.printstacktrace ();        } t2.start ();    T3.start (); }}

• Example:

 Package Com.xuweiwei;  Public class extends Thread {    @Override    publicvoid  run () {        for (int i = 0; I < 100; i++) {            + "=" + i);            Thread.yield ();     }}}

 PackageCom.xuweiwei; Public classMythreadtest { Public Static voidMain (string[] args) {MyThread T1=NewMyThread (); MyThread T2=NewMyThread (); MyThread T3=NewMyThread (); T1.setname ("Liyuan"); T2.setname ("Li Jiancheng"); T3.setname ("Li Shimin");        T1.start ();        T2.start ();    T3.start (); }}

• Example:

 Package Com.xuweiwei;  Public class extends Thread {    @Override    publicvoid  run () {        for (  int i = 0; I < 100; i++) {            + "=" + i);            Thread.yield ();     }}}

 PackageCom.xuweiwei; Public classMythreadtest { Public Static voidMain (string[] args) {MyThread t2=NewMyThread (); MyThread T3=NewMyThread (); T2.setname ("Li Jiancheng"); T3.setname ("Li Shimin"); T2.setdaemon (true); T3.setdaemon (true);        T2.start ();        T3.start (); Thread.CurrentThread (). SetName ("Liyuan");  for(inti = 0; I < 3; i++) {System.out.println (Thread.CurrentThread (). GetName ()+"= " +i); }    }}

2.4 The life cycle of a thread

• NEW: Create thread object.
• Ready: There is an executive qualification, but no enforcement right.
• Run: Have the execution qualification, have the execution right.
• Blocking: The thread is in that state due to some actions. No executive qualification, no executive right.
• Death: The Thread object object becomes garbage and waits to be recycled.

2.5 Multi-Threading Implementation mode two

• Steps:
• ①

3 thread scheduling and line programming

4 Thread life cycle

5 dead Lock

6 Inter-thread communication

7 Use of Timers

Java Fundamentals 22