sleep和wait的區(qū)別是面試中一個(gè)非常常見(jiàn)的問(wèn)題，因?yàn)閺谋硐髞?lái)看散址，好像sleep和wait都能使線程處于阻塞狀態(tài)乖阵，但是卻有著本質(zhì)上的卻別宣赔。
- sleep是線程類Thread的方法，但是wait是java對(duì)象老祖宗Object中的方法瞪浸。
- sleep方法不會(huì)釋放lock儒将，但是wait會(huì)釋放，而且會(huì)加入到等待隊(duì)列中对蒲。
- sleep方法不依賴于同步器synchronized钩蚊，但是wait需要依賴synchronized關(guān)鍵字。
- sleep不需要被喚醒（休眠之后推出阻塞）蹈矮，但是wait需要（不指定時(shí)間需要被別人中斷）两疚。
區(qū)別一 : sleep是線程方法，wait是Object方法
通過(guò)一些代碼來(lái)看看區(qū)別二：
package com.xy.Multithreading;
import java.util.stream.Stream;
public class Demo1 {
private final static Object sign = new Object();
public static void TestSleep(){
synchronized(sign){
try {
System.out.println(Thread.currentThread().getName()+"執(zhí)行TestSleep方法");
Thread.sleep(5000);
System.out.println(Thread.currentThread().getName()+"休眠結(jié)束");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args){
Stream.of("線程1","線程2").forEach(n->new Thread(n){
@Override
public void run() {
Demo1.TestSleep();
}
}.start());
}
}
package com.xy.Multithreading;
import java.util.stream.Stream;
public class Demo2 {
private final static Object sign = new Object();
public static void TestWait(){
synchronized(sign){
try {
System.out.println(Thread.currentThread().getName()+"執(zhí)行TestWait方法");
sign.wait(10000);
System.out.println(Thread.currentThread().getName()+"TestWait結(jié)束");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args){
Stream.of("線程1","線程2").forEach(n->new Thread(n){
@Override
public void run() {
Demo2.TestWait();
}
}.start());
}
}
package com.xy.Multithreading;
import java.util.stream.Stream;
public class Demo3 {
private final static Object sign = new Object();
public static void TestWait(){
synchronized(sign){
try {
System.out.println(Thread.currentThread().getName()+"執(zhí)行TestWait方法");
Thread.sleep(5000);
System.out.println(Thread.currentThread().getName()+"sleep結(jié)束");
sign.wait(10000);
System.out.println(Thread.currentThread().getName()+"TestWait結(jié)束");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args){
Stream.of("線程1","線程2").forEach(n->new Thread(n){
@Override
public void run() {
Demo3.TestWait();
}
}.start());
}
}
package com.xy.Multithreading;
import java.util.Date;
import java.util.stream.Stream;
public class Demo4 {
private final static Object sign = new Object();
public static void TestWait(){
synchronized(sign){
try {
long beginTime = System.currentTimeMillis();
System.out.println(Thread.currentThread().getName()+"執(zhí)行TestWait方法含滴，當(dāng)前時(shí)間："+new Date().toString());
Thread.sleep(5000);
long time = System.currentTimeMillis();
System.out.println(Thread.currentThread().getName()+"sleep結(jié)束诱渤，"+"從線程執(zhí)行run到現(xiàn)在花的時(shí)間："
+(time-beginTime)+"，當(dāng)前時(shí)間："+new Date().toString());
sign.wait(12000);
long endTime = System.currentTimeMillis();
System.out.println(Thread.currentThread().getName()+"TestWait結(jié)束,"
+"從線程執(zhí)行run到現(xiàn)在花的時(shí)間："+(endTime-beginTime)+"谈况，當(dāng)前時(shí)間："+new Date().toString());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args){
Stream.of("線程1","線程2","線程3").forEach(n->new Thread(n){
@Override
public void run() {
Demo4.TestWait();
}
}.start());
}
}
區(qū)別二：sleep不釋放鎖勺美，wait會(huì)讓當(dāng)前線程釋放鎖
- 執(zhí)行demo1代碼，首先打印"線程1執(zhí)行TestSleep方法",然后線程1睡眠5秒后碑韵，接著幾乎同時(shí)打印出"test1休眠結(jié)束"和"test2執(zhí)行TestSleep方法"赡茸，線程2睡眠5秒后，接著打印"test2休眠結(jié)束"祝闻。
- 執(zhí)行demo2代碼占卧，首先幾乎同時(shí)打印"線程1執(zhí)行TestWait方法和線程2執(zhí)行TestWait方法",然后等待5秒后幾乎同時(shí)打印"線程2TestWait結(jié)束"和"線程1TestWait結(jié)束".
- 執(zhí)行ddemo3代碼，首先打印"線程1執(zhí)行TestWait方法",5秒后幾乎同時(shí)打印"線程1sleep結(jié)束"和"線程2執(zhí)行TestWait方法",再過(guò)5秒后打印"線程2sleep結(jié)束",再過(guò)5秒打印"線程1TestWait結(jié)束",再過(guò)5秒打印"線程2TestWait結(jié)束".
- 執(zhí)行demo4代碼:
"C:\Program Files\Java\jdk1.8.0_111\bin\java.exe" "-javaagent:D:\IDEA\IntelliJ IDEA Free2020.1\IntelliJ IDEA Community Edition 2020.1\lib\idea_rt.jar=55642:D:\IDEA\IntelliJ IDEA Free2020.1\IntelliJ IDEA Community Edition 2020.1\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_111\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_111\jre\lib\rt.jar;E:\ideaWorkspace\target\classes;C:\Users\96935\.m2\repository\org\springframework\boot\spring-boot-starter\2.2.6.RELEASE\spring-boot-starter-2.2.6.RELEASE.jar;C:\Users\96935\.m2\repository\org\springframework\boot\spring-boot\2.2.6.RELEASE\spring-boot-2.2.6.RELEASE.jar;C:\Users\96935\.m2\repository\org\springframework\spring-context\5.2.5.RELEASE\spring-context-5.2.5.RELEASE.jar;C:\Users\96935\.m2\repository\org\springframework\spring-aop\5.2.5.RELEASE\spring-aop-5.2.5.RELEASE.jar;C:\Users\96935\.m2\repository\org\springframework\spring-beans\5.2.5.RELEASE\spring-beans-5.2.5.RELEASE.jar;C:\Users\96935\.m2\repository\org\springframework\spring-expression\5.2.5.RELEASE\spring-expression-5.2.5.RELEASE.jar;C:\Users\96935\.m2\repository\org\springframework\boot\spring-boot-autoconfigure\2.2.6.RELEASE\spring-boot-autoconfigure-2.2.6.RELEASE.jar;C:\Users\96935\.m2\repository\org\springframework\boot\spring-boot-starter-logging\2.2.6.RELEASE\spring-boot-starter-logging-2.2.6.RELEASE.jar;C:\Users\96935\.m2\repository\ch\qos\logback\logback-classic\1.2.3\logback-classic-1.2.3.jar;C:\Users\96935\.m2\repository\ch\qos\logback\logback-core\1.2.3\logback-core-1.2.3.jar;C:\Users\96935\.m2\repository\org\apache\logging\log4j\log4j-to-slf4j\2.12.1\log4j-to-slf4j-2.12.1.jar;C:\Users\96935\.m2\repository\org\apache\logging\log4j\log4j-api\2.12.1\log4j-api-2.12.1.jar;C:\Users\96935\.m2\repository\org\slf4j\jul-to-slf4j\1.7.30\jul-to-slf4j-1.7.30.jar;C:\Users\96935\.m2\repository\jakarta\annotation\jakarta.annotation-api\1.3.5\jakarta.annotation-api-1.3.5.jar;C:\Users\96935\.m2\repository\org\springframework\spring-core\5.2.5.RELEASE\spring-core-5.2.5.RELEASE.jar;C:\Users\96935\.m2\repository\org\springframework\spring-jcl\5.2.5.RELEASE\spring-jcl-5.2.5.RELEASE.jar;C:\Users\96935\.m2\repository\org\yaml\snakeyaml\1.25\snakeyaml-1.25.jar;C:\Users\96935\.m2\repository\org\projectlombok\lombok\1.18.12\lombok-1.18.12.jar;C:\Users\96935\.m2\repository\cglib\cglib\3.2.9\cglib-3.2.9.jar;C:\Users\96935\.m2\repository\org\ow2\asm\asm\7.0\asm-7.0.jar;C:\Users\96935\.m2\repository\org\apache\ant\ant\1.10.3\ant-1.10.3.jar;C:\Users\96935\.m2\repository\org\apache\ant\ant-launcher\1.10.3\ant-launcher-1.10.3.jar;C:\Users\96935\.m2\repository\org\slf4j\slf4j-api\1.7.30\slf4j-api-1.7.30.jar" com.xy.Multithreading.Demo4
線程1執(zhí)行TestWait方法联喘，當(dāng)前時(shí)間：Tue May 12 20:49:10 CST 2020
線程1sleep結(jié)束华蜒，從線程執(zhí)行run到現(xiàn)在花的時(shí)間：5028，當(dāng)前時(shí)間：Tue May 12 20:49:15 CST 2020
線程3執(zhí)行TestWait方法豁遭，當(dāng)前時(shí)間：Tue May 12 20:49:15 CST 2020
線程3sleep結(jié)束叭喜，從線程執(zhí)行run到現(xiàn)在花的時(shí)間：5000，當(dāng)前時(shí)間：Tue May 12 20:49:20 CST 2020
線程2執(zhí)行TestWait方法蓖谢，當(dāng)前時(shí)間：Tue May 12 20:49:20 CST 2020
線程2sleep結(jié)束捂蕴，從線程執(zhí)行run到現(xiàn)在花的時(shí)間：5001，當(dāng)前時(shí)間：Tue May 12 20:49:25 CST 2020
線程1TestWait結(jié)束,從線程執(zhí)行run到現(xiàn)在花的時(shí)間：17028闪幽，當(dāng)前時(shí)間：Tue May 12 20:49:27 CST 2020
線程3TestWait結(jié)束,從線程執(zhí)行run到現(xiàn)在花的時(shí)間：17000啥辨，當(dāng)前時(shí)間：Tue May 12 20:49:32 CST 2020
線程2TestWait結(jié)束,從線程執(zhí)行run到現(xiàn)在花的時(shí)間：17001，當(dāng)前時(shí)間：Tue May 12 20:49:37 CST 2020
Process finished with exit code 0
結(jié)論：執(zhí)行wait方法的時(shí)候盯腌，當(dāng)前線程會(huì)釋放被synchronized鎖住的代碼塊和對(duì)象溉知，但并不是讓synchronized失效。從demo4可以看出，線程1釋放鎖之后着倾，synchronized(sign){...}代碼塊馬上被線程3執(zhí)行并加鎖拾酝，當(dāng)線程3執(zhí)行wait方法后又會(huì)釋放鎖，線程2才能執(zhí)行這塊代碼卡者。
