Multi-threaded Knowledge Base

Basic concepts

　process is the execution of a task, is a program and its data in the processing machine sequential execution of the activity occurs, the popular point of the Windows system each running EXE is a process, a process has multiple threads

　　threads can be understood as subtasks that run independently in a process.

Why use Multithreading

It says that threads are sub-tasks that run independently in a process, single-threaded, that is, when a single task, each task is executed sequentially, synchronously. For example, there are two tasks A and b,a tasks are waiting to download the file, the time is 5s,cpu in the waiting state, the b task only needs 1s, even if the b task is just 1s, also need a 5s execution end to execute B.

Multi-threading, the CPU can switch between task A and task B, so that task B does not need to wait for a after execution, improve the efficiency of the system, which is the advantage of multithreading, that is, asynchronous.

How threads are Created

Way one: Inherit thread, the disadvantage is that Java only supports single inheritance, actually see the source code thread class is also implemented Runnable interface

Method Two (recommended): Implement the Runnable interface, generally use this method (when the class itself has inherited a class, you can use to implement the interface this way)

Inherit thread mode

public class MyThread2 extends thread{    @Override public    void Run () {        try {for            (int i=0;i<10;i++) {                int time = (int) (Math.random () * +);                Thread.Sleep (time);                System.out.println ("run=" + thread.currentthread (). GetName ());            }        } catch (Interruptedexception e) {            e.printstacktrace ();        }    }    public static void Main (string[] args) {        MyThread2 myThread2 = new MyThread2 ();        Mythread2.start ();//start thread        try {for            (int i=0;i<10;i++) {                int time = (int) (Math.random () *1000);                Thread.Sleep (time);                System.out.println ("main=" +thread.currentthread (). GetName ());            }        } catch (Interruptedexception e) {            e.printstacktrace ();}}    }

Run results

run=thread-0Main=mainrun=thread-0main=mainrun=thread-0Run= Thread-0Main=mainrun=thread-0main=mainrun=thread-0main=  Mainrun=thread-0main=mainmain=Mainmain=mainrun=thread-0  Run=thread-0main=mainmain=mainrun=thread-0

From the results of the run: Code run results and code execution order independent, the above code has an asynchronous effect

The Thread.Start () method is to start a thread, and if you execute run directly (), it is actually equivalent to executing a method in Java order.

Implementing the runnable Approach

public class Myrunnable implements Runnable {public    void run () {        System.out.println (Thread.CurrentThread (). GetName ());    }    public static void Main (string[] args) {        myrunnable runnable = new myrunnable ();        Thread thread = new Thread (runnable);        Thread.Start ();        System.out.println ("end!!");}    }

　　

Run results

end!! Thread-0

　　

There are only two types of thread implementations, but there are many forms of expression

Example 1:

public static void Main (string[] args) {        thread thread = new Thread (new Runnable () {public            void run () {                syste M.out.println (Thread.CurrentThread (). GetName ());            }        );        Thread.Start ();        System.out.println ("end!!"); }

Example 2:

public static void Main (string[] args) {        Runnable Runnable = new Runnable () {public            void run () {                SYSTEM.OUT.P Rintln (Thread.CurrentThread (). GetName ());            }        ;        Thread thread = new Thread (runnable);        Thread.Start ();        System.out.println ("end!!");}

　　

　

Multi-threaded Knowledge Base