Java核心類庫(kù)篇7——多線程

1、程序、進(jìn)程和線程

• 程序 - 數(shù)據(jù)結(jié)構(gòu) + 算法，主要指存放在硬盤上的可執(zhí)行文件
• 進(jìn)程 - 主要指運(yùn)行在內(nèi)存中的可執(zhí)行文件
• 線程就是進(jìn)程內(nèi)部的程序流

操作系統(tǒng)內(nèi)部支持多 進(jìn)程的，而每個(gè)進(jìn)程的內(nèi)部又是支持多線程的

2、線程的創(chuàng)建

方法聲明功能介紹

public Thread()	使用無(wú)參的方式構(gòu)造對(duì)象
public Thread(String name)	根據(jù)參數(shù)指定的名稱來(lái)構(gòu)造對(duì)象
public Thread(Runnable target)	根據(jù)參數(shù)指定的引用來(lái)構(gòu)造對(duì)象，其中Runnable是個(gè)接口類型
public Thread(Runnable target, String name)	根據(jù)參數(shù)指定引用和名稱來(lái)構(gòu)造對(duì)象
public void run()	若使用Runnable引用構(gòu)造了線程對(duì)象，調(diào)用該方法時(shí)最終調(diào) 用接口中的版本 若沒(méi)有使用Runnable引用構(gòu)造線程對(duì)象，調(diào)用該方法時(shí)則啥也不做
public void start()	用于啟動(dòng)線程，Java虛擬機(jī)會(huì)自動(dòng)調(diào)用該線程的run方法
public long getId()	獲取調(diào)用對(duì)象所表示線程的編號(hào)
public String getName()	獲取調(diào)用對(duì)象所表示線程的名稱
public void setName(String name)	設(shè)置/修改線程的名稱為參數(shù)指定的數(shù)值
public static Thread currentThread()	獲取當(dāng)前正在執(zhí)行線程的引用

2.1、繼承Thread類

• 優(yōu)點(diǎn)：實(shí)現(xiàn)起來(lái)簡(jiǎn)單，而且要獲取當(dāng)前線程，無(wú)需調(diào)用Thread.currentThread()方法，直接使用this即可獲取當(dāng)前線程
• 缺點(diǎn)：線程類已經(jīng)繼承Thread類了，就不能再繼承其他類，多個(gè)線程不能共享同一份資源

public class MyThread extends Thread {@Overridepublic void run() {for (int i = 0; i < 50; i++) {System.out.println(this.getName()+"----------------"+i);}} } public class Test {public static void main(String[] args) {new MyThread().start();for (int i = 0; i < 50; i++) {System.out.println(Thread.currentThread().getName()+"----------------"+i);}} }

注：直接調(diào)用run方法如同調(diào)用類成員方法一樣

2.2、實(shí)現(xiàn)Runnable接口

• 優(yōu)點(diǎn)：線程類只是實(shí)現(xiàn)了接口，還可以繼承其他類，多個(gè)線程可以使用同一個(gè)target對(duì)象，適合多個(gè)線程處理同一份資源的情況
• 缺點(diǎn)：通過(guò)這種方式實(shí)現(xiàn)多線程，相較于第一類方式，編程較復(fù)雜，要訪問(wèn)當(dāng)前線程，必須調(diào)用Thread.currentThread()方法

public class MyRunable implements Runnable {@Overridepublic void run() {for (int i = 0; i < 50; i++) {System.out.println(Thread.currentThread().getName()+"----------------"+i);}} } public class Test {public static void main(String[] args) {new Thread(new MyRunable()).start();for (int i = 0; i < 50; i++) {System.out.println(Thread.currentThread().getName()+"----------------"+i);}} }

2.3、Callable和FutureTask

• 優(yōu)點(diǎn)：線程類只是實(shí)現(xiàn)了接口，還可以繼承其他類，多個(gè)線程可以使用同一個(gè)target對(duì)象，適合多個(gè)線程處理同一份資源的情況
• 缺點(diǎn)：通過(guò)這種方式實(shí)現(xiàn)多線程，相較于第一類方式，編程較復(fù)雜，要訪問(wèn)當(dāng)前線程，必須調(diào)用Thread.currentThread()方法

public class Test {public static void main(String[] args) throws ExecutionException, InterruptedException {FutureTask<Integer> futureTask=new FutureTask<Integer>(new Callable<Integer>() {@Overridepublic Integer call() throws Exception {for (int i = 0; i < 50; i++) {System.out.println(Thread.currentThread().getName()+"----------------"+i);}return 100;}});new Thread(futureTask, "ruoye").start();for (int i = 0; i < 50; i++) {System.out.println(Thread.currentThread().getName()+"----------------"+i);}System.out.println(futureTask.get());} }

lambda表達(dá)式

public class Test {public static void main(String[] args) throws ExecutionException, InterruptedException {FutureTask<Integer> futureTask = new FutureTask<>((Callable<Integer>) () -> {System.out.println("hello world!");return 100;});new Thread(futureTask, "ruoye").start();for (int i = 0; i < 50; i++) {System.out.println(Thread.currentThread().getName()+"----------------"+i);}System.out.println(futureTask.get());} }

3、線程優(yōu)先級(jí)及線程讓步

方法聲明功能介紹

public static void yield()	當(dāng)前線程讓出處理器（離開(kāi)Running狀態(tài)），使當(dāng)前線程進(jìn)入Runnable 狀態(tài)等待
public static void sleep(times)	使當(dāng)前線程從 Running 放棄處理器進(jìn)入Block狀態(tài), 休眠times毫秒
public int getPriority()	獲取線程的優(yōu)先級(jí)
public void setPriority(int newPriority)	修改線程的優(yōu)先級(jí)，優(yōu)先級(jí)越高的線程不一定先執(zhí)行，但該線程獲取到時(shí)間片的機(jī)會(huì)會(huì)更多 一些
public void join()	等待該線程終止
public void join(long millis)	等待參數(shù)指定的毫秒數(shù)
public boolean isDaemon()	用于判斷是否為守護(hù)線程
public void setDaemon(boolean on)	用于設(shè)置線程為守護(hù)線程

sleep

public class Test {public static void main(String[] args) {SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");while (true){System.out.println(simpleDateFormat.format(new Date()));try {Thread.sleep(2000);} catch (InterruptedException e) {e.printStackTrace();}}} }

setPriority線程優(yōu)先級(jí)

public class Test {public static void main(String[] args) {Thread thread = new Thread(() -> {System.out.println(Thread.currentThread().getName()+"優(yōu)先級(jí)-----"+Thread.currentThread().getPriority());for (int i = 0; i < 100; i++) {System.out.println(Thread.currentThread().getName()+"-----"+i);}});thread.setName("ruoye");thread.setPriority(Thread.MAX_PRIORITY);thread.start();for (int i = 0; i < 100; i++) {System.out.println(Thread.currentThread().getName()+"-----"+i);}} }

線程等待

public class Test {public static void main(String[] args) throws InterruptedException {Thread thread = new Thread(() -> {for (int i = 0; i < 10; i++) {try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}System.out.println(Thread.currentThread().getName()+"-----"+i);}});thread.setName("ruoye");thread.start(); // thread.join(); // System.out.println("終于等到你");thread.join(5000);System.out.println("沒(méi)有等到你");} }

守護(hù)線程

public class Test {public static void main(String[] args) throws InterruptedException {Thread thread = new Thread(() -> {for (int i = 0; i < 10; i++) {try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}System.out.println(Thread.currentThread().getName()+"-----"+i);}});thread.setName("ruoye");thread.setDaemon(true);thread.start();Thread.sleep(5000);System.out.println("沒(méi)有等到你");} }

4、線程同步

4.1、多線程出現(xiàn)的問(wèn)題

public class Account implements Runnable {private int money;public Account(int money) {this.money = money;}public int getMoney() {return money;}public void setMoney(int money) {this.money = money;}@Overridepublic void run() {System.out.println("進(jìn)到門口");System.out.println("開(kāi)始取鈔");if (this.money>200){try {Thread.sleep(3000);} catch (InterruptedException e) {e.printStackTrace();}this.money-=200;System.out.println("取款成功");}}@Overridepublic String toString() {return "Account{" +"money=" + money +'}';} } public class Test {public static void main(String[] args) throws InterruptedException {Account account = new Account(1000);Thread thread = new Thread(account);Thread thread1 = new Thread(account);thread.start();thread1.start();thread.join();thread1.join();System.out.println(account.getMoney());} }

4.2、synchronized同步鎖

4.2.1、synchronized代碼塊

下面所示為鎖class，鎖Account對(duì)象里的成員變量（對(duì)象）也可，但請(qǐng)時(shí)刻記住，多個(gè)Account為對(duì)象里的成員變量（對(duì)象）多個(gè)對(duì)象，那么就擁有了多把鎖，此時(shí)應(yīng)當(dāng)用static修飾

休眠在同步代碼塊內(nèi)不會(huì)讓出cpu

public class Account implements Runnable {private int money;public Account(int money) {this.money = money;}public int getMoney() {return money;}public void setMoney(int money) {this.money = money;}@Overridepublic void run() {System.out.println("進(jìn)到門口");synchronized (Account.class){System.out.println("開(kāi)始取鈔");if (this.money>200){try {Thread.sleep(3000);} catch (InterruptedException e) {e.printStackTrace();}this.money-=200;System.out.println("取款成功");}}}@Overridepublic String toString() {return "Account{" +"money=" + money +'}';} } public class Test {public static void main(String[] args) throws InterruptedException {Account account = new Account(1000);Thread thread = new Thread(account);Thread thread1 = new Thread(account);thread.start();thread1.start();thread.join();thread1.join();System.out.println(account.getMoney());} }

4.2.2、synchronized方法

當(dāng)synchronized位于成員方法上等價(jià)于synchronized (this)

當(dāng)當(dāng)synchronized位于成員方法上等價(jià)于synchronized (類對(duì)象)

public class Account implements Runnable {private int money;public Account(int money) {this.money = money;}public int getMoney() {return money;}public void setMoney(int money) {this.money = money;}@Overridepublic synchronized void run() {System.out.println("進(jìn)到門口");System.out.println("開(kāi)始取鈔");if (this.money>200){try {Thread.sleep(3000);} catch (InterruptedException e) {e.printStackTrace();}this.money-=200;System.out.println("取款成功");}}@Overridepublic String toString() {return "Account{" +"money=" + money +'}';} } public class Test {public static void main(String[] args) throws InterruptedException {Account account = new Account(1000);Thread thread = new Thread(account);Thread thread1 = new Thread(account);thread.start();thread1.start();thread.join();thread1.join();System.out.println(account.getMoney());} }

4.3、死鎖問(wèn)題

盡量減少同步的資源，減少同步代碼塊的嵌套結(jié)構(gòu)的使用

線程一執(zhí)行的代碼

public void run(){synchronized(a){ //持有對(duì)象鎖a，等待對(duì)象鎖b synchronized(b){ //編寫鎖定的代碼; }} }

線程二執(zhí)行的代碼

public void run(){synchronized(b){ //持有對(duì)象鎖a，等待對(duì)象鎖b synchronized(a){ //編寫鎖定的代碼; }} }

4.4、Lock鎖

• Lock是顯式鎖，需要手動(dòng)實(shí)現(xiàn)開(kāi)啟和關(guān)閉操作，而synchronized是隱式鎖，執(zhí)行鎖定代碼后自動(dòng)釋放
• Lock只有同步代碼塊方式的鎖，而synchronized有同步代碼塊方式和同步方法兩種鎖
• 使用Lock鎖方式時(shí)，Java虛擬機(jī)將花費(fèi)較少的時(shí)間來(lái)調(diào)度線程，因此性能更好

public class Account implements Runnable {private int money;private static Lock lock=new ReentrantLock();public Account(int money) {this.money = money;}public int getMoney() {return money;}public void setMoney(int money) {this.money = money;}@Overridepublic void run() {lock.lock();System.out.println("進(jìn)到門口");System.out.println("開(kāi)始取鈔");if (this.money>200){try {Thread.sleep(3000);} catch (InterruptedException e) {e.printStackTrace();}this.money-=200;System.out.println("取款成功");}lock.unlock();}@Overridepublic String toString() {return "Account{" +"money=" + money +'}';} } public class Test {public static void main(String[] args) throws InterruptedException {Account account = new Account(1000);Thread thread = new Thread(account);Thread thread1 = new Thread(account);thread.start();thread1.start();thread.join();thread1.join();System.out.println(account.getMoney());} }

5、線程通信

5.1、線程通信

不能鎖class

public class Account implements Runnable {private int a;public Account(int a) {this.a = a;}@Overridepublic void run() {while (true){synchronized (this) {if (a<100){System.out.println(Thread.currentThread().getName()+"========"+a);a++;notify();try {wait();} catch (InterruptedException e) {e.printStackTrace();}}else{break;}}}} } public class Test {public static void main(String[] args) throws InterruptedException {Account account = new Account(1);Thread ruoye = new Thread(account, "ruoye");Thread yoya = new Thread(account, "yoya");ruoye.start();yoya.start();} }

5.2、生產(chǎn)者消費(fèi)者問(wèn)題

• 線程間的通信共享數(shù)據(jù)一定要有同步代碼塊synchronized
• 一定要有wait和notify，而且二者一定是成對(duì)出現(xiàn)
• 生產(chǎn)者和消費(fèi)者的線程實(shí)現(xiàn)一定是在while（true）里面

public class Mother implements Runnable {private Account account;public Mother(Account account) {this.account = account;}@Overridepublic void run() {while (true){try {account.produce();Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}}} } public class Ming implements Runnable {private Account account;public Ming(Account account) {this.account = account;}@Overridepublic void run() {while (true){try {account.consumer();Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}}} } public class Account {private int a;public Account(int a) {this.a = a;}public int getA() {return a;}public void setA(int a) {this.a = a;}public synchronized void produce() throws InterruptedException {notify();if (a<2000){a+=100;System.out.println("媽媽給小明存了100元");}else{wait();}}public synchronized void consumer() throws InterruptedException {notify();if (a>75){a-=75;System.out.println("小明花了75元");}else{wait();}} } public class Test {public static void main(String[] args) throws InterruptedException {Account account = new Account(0);new Thread(new Mother(account)).start();new Thread(new Ming(account)).start();} }

總結(jié)

以上是生活随笔為你收集整理的Java核心类库篇7——多线程的全部?jī)?nèi)容，希望文章能夠幫你解決所遇到的問(wèn)題。

如果覺(jué)得生活随笔網(wǎng)站內(nèi)容還不錯(cuò)，歡迎將生活随笔推薦給好友。