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This article mainly introduces Java how to achieve multithreading, thread synchronization related knowledge, the content is detailed and easy to understand, the operation is simple and fast, has a certain reference value, I believe that after reading this Java how to achieve multithreading, thread synchronization article will have a harvest, let's take a look.

1 multithreaded 1.1 process

Process: is a running program

It is an independent unit for the system to allocate and invoke resources.

Each process has its own memory space and system resources.

Three characteristics of the process

Independence: processes are independent of each other and have their own independent memory areas.

Dynamic: a process is a running program that dynamically takes up memory, CPU, network and other resources.

Concurrency: CPU will time-sharing polling switching to serve each process in turn, because the switching speed is so fast that it makes us feel as if we are executing at the same time, which is concurrency (concurrency: multiple processes are executed at the same time)

1.2 Thread

Thread: is a single sequential control flow in a process and is an execution path

Single thread: a process has only one execution path

Multithreading: a process has multiple execution paths

1.3Multithreading implementation 1.3.1 method 1: inherit Tread class

Process:

1. Define a MyTread class that inherits the Tread class

2. Override run () method in the MyTread class

3. Create an object of the MyTread class

4. Start the thread: void start ()

Why override the run () method?

Because run () is used to encapsulate the code executed by the thread

What is the difference between run () method and start () method?

Run (): code executed by the wrapper thread, called directly, equivalent to a call to a normal method

Start (): starts the thread, and then calls the run () method in this thread by JVM

Example

MyTread class:

Package test;//1, define a class of MyTread inheriting Tread class public class MyThread extends Thread {2, override the run () method @ Override public void run () {for (int item0 / Thread.sleep) {/ / try {/ / Thread.sleep (100) in the MyTread class; / /} catch (InterruptedException e) {/ / e.printStackTrace () / /} / / System.out.println (Thread.currentThread (). GetName () + "for sale" + tickets + "ticket"); / / tickets--; / / tickets=99//} / /} private static synchronized void sellTicket () {if (tickets > 0) {try {Thread.sleep (100) } catch (InterruptedException e) {e.printStackTrace ();} System.out.println (Thread.currentThread (). GetName () + "being sold" + tickets + "ticket"); tickets--; / / tickets=99}} 1.11Thread-safe classes (see)

The methods in the source code are all modified by synchronized

StringBuffer

Thread-safe, variable character sequence

Starting with version JDK 5, it was replaced by StringBuilder. You should usually use the StringBuilder class because it supports all the same operations, but it is faster because it does not perform synchronization

Vector

Starting with the Java 2 platform v1.2, this class improves the List interface to make it a member of Java Collections Framework. Unlike the new collection implementation, Vector is synchronized. If you do not need a thread-safe implementation, it is recommended to use ArrayList instead of Vector

Hashtable

This class implements a hash table that maps keys to values. Any non-null object can be used as a key or value

Starting with the Java 2 platform v1.2, this class has been improved to implement the Map interface, making it a member of Java Collections Framework. Unlike the new collection implementation, Hashtable is synchronized. If you do not need a thread-safe implementation, it is recommended to use HashMap instead of Hashtable

Static List snchronizedList (List list) in the Collections class: returns a list of synchronization (thread safety) supported by the specified list

Package test;import java.util.ArrayList;import java.util.Collection;import java.util.Collections;public class Demo {public static void main (String [] args) {/ / static List snchronizedList (List list): returns a list of synchronization (thread safety) supported by the specified list Collection list = Collections.synchronizedList (new ArrayList ()); / * the source code returns Synchronized public static List synchronizedList (List list) {return (list instanceof RandomAccess? New Collections.SynchronizedRandomAccessList (list): new Collections.SynchronizedList (list));} * /} 1.12Lock lock

Lock is an interface that cannot be instantiated directly, so it is instantiated using the implementation class ReentrantLock (after JDK5)

ReentrantLock construction method:

The method name indicates that ReentrantLock () creates an instance object of ReentrantLock

The method of acquiring and releasing locks in Lock:

The method name indicates that void lock () acquires the lock void unlock () releases the lock

It is recommended to use try {} finall {} code blocks to lock and release locks

Package test;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;public class SellTicket implements Runnable {private static int tickets = 100; private Lock lock = new ReentrantLock (); @ Override public void run () {while (true) {try {lock.lock () If (tickets > 0) {try {Thread.sleep (100);} catch (InterruptedException e) {e.printStackTrace () } System.out.println (Thread.currentThread (). GetName () + "being sold" + tickets + "ticket"); tickets--;}} finally {lock.unlock ();} 1.13 thread communication

Thread communication must be when multiple threads are operating the same resource in order to communicate.

The method name indicates that public void wait () puts the current thread into a waiting state. This method must call public void notify () to wake up a thread in the waiting state on the current lock object. This method must call public void notifyAll () to wake up all threads in the waiting state on the current lock object. This method must call 1.14 producer consumer 1.14.1 producer consumer overview.

In order to reflect the waiting and awakening in the process of production and consumption, Java provides several methods for us to use, which are in the Object class.

Wait and Wake up methods of Object Class

The method name indicates that void wait () causes the current thread to wait until another thread calls the object's notify () method or notifyAll () method void notify () wakes up a single thread waiting for the object monitor void notifyAll () wakes up all threads waiting for the object monitor 1.14.2 producer consumer case

Milk box class

Package test;//1: define the milk box class public class Box {/ / define a member variable to represent the x bottle of milk private int milk; / / define a member variable to represent the state of the milk box private boolean state = false / / provide the operation of storing and obtaining milk public synchronized void put (int milk) {/ / if there is milk waiting for consumption if (state) {try {wait ();} catch (InterruptedException e) {e.printStackTrace () }} / / if there is no milk, produce milk this.milk = milk; System.out.println ("the milkman will put the milk in the milk box" + this.milk + "bottle milk"); / / after the production is finished, modify the status of the milk box state = true; / / wake up other waiting threads notifyAll () } public synchronized void get () {/ / if there is no milk, wait until if (! state) {try {wait ();} catch (InterruptedException e) {e.printStackTrace () }} / / if there is milk, consume milk System.out.println ("user gets first" + this.milk + "bottle milk"); / / after consumption, modify the milk box status state = false; / / wake up other waiting threads notifyAll ();}}

Producer class

Package test;//2: producer class (Producer): implement the Runnable interface public class Producer implements Runnable {private Box b; public Producer (Box b) {this.b = b;} / / override the run () method, and call the operation @ Override public void run () {for (int I = 1; I) for storing milk.

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