《Java多线程编程核心技术》读后感（六）
多线程的死锁
package Second;
public class DealThread implements Runnable {
public String username;
public Object lock1 = new Object();
public Object lock2 = new Object();
public void setFlag(String username) {
this.username = username;
}
@Override
public void run() {
if (username.equals("a")) {
synchronized (lock1) {
try {
System.out.println("username = " + username);
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
synchronized (lock2) {
System.out.println("按lock1->lock2代码顺序执行了");
}
}
}
if (username.equals("b")) {
synchronized (lock2) {
try {
System.out.println("username = " + username);
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
synchronized (lock1) {
System.out.println("按lock2->lock1代码顺序执行了");
}
}
}
}
}
只要互相等待对方释放锁就有可能出现死锁
内置类与静态内置类
package Second;
public class PublicClass {
private String username;
private String password;
class PrivateClass {
private String age;
private String address;
public String getAge() {
return age;
}
public void setAge(String age) {
this.age = age;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public void printPublicProperty() {
System.out.println(username + " " + password);
}
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
package Second;
import Second.PublicClass.PrivateClass;
public class Run {
public static void main(String[] args) {
PublicClass publicClass = new PublicClass();
publicClass.setUsername("usernameValue");
publicClass.setPassword("passwordValue");
System.out.println(publicClass.getUsername() + " "
+ publicClass.getPassword());
PrivateClass privateClass = publicClass.new PrivateClass();
privateClass.setAge("ageValue");
privateClass.setAddress("addressValue");
System.out.println(privateClass.getAge() + " "
+ privateClass.getAddress());
}
}
package Second;
public class PublicClass {
static private String username;
static private String password;
static class PrivateClass {
private String age;
private String address;
public String getAge() {
return age;
}
public void setAge(String age) {
this.age = age;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public void printPublicProperty() {
System.out.println(username + " " + password);
}
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
package Second;
import Second.PublicClass.PrivateClass;
public class Run {
public static void main(String[] args) {
PublicClass publicClass = new PublicClass();
publicClass.setUsername("usernameValue");
publicClass.setPassword("passwordValue");
System.out.println(publicClass.getUsername() + " "
+ publicClass.getPassword());
PrivateClass privateClass = new PrivateClass();
privateClass.setAge("ageValue");
privateClass.setAddress("addressValue");
System.out.println(privateClass.getAge() + " "
+ privateClass.getAddress());
}
}
内置类与同步：实验1
本实验案例是在内置类中有两个同步方法，但使用的却是不同的锁，打印的结果也是异步的。
package Second;
public class OutClass {
static class Inner {
public void method1() {
synchronized ("其他的鎖") {
for (int i = 1; i <= 10; i++) {
System.out.println(Thread.currentThread().getName() + " i="
+ i);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
}
}
}
}
public synchronized void method2() {
for (int i = 11; i <= 20; i++) {
System.out.println(Thread.currentThread().getName() + " i=" + i);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
}
}
}
}
}
package Second;
import Second.OutClass.Inner;
public class Run {
public static void main(String[] args) {
final Inner inner = new Inner();
Thread t1 = new Thread(new Runnable() {
public void run() {
inner.method1();
}
}, "A");
Thread t2 = new Thread(new Runnable() {
public void run() {
inner.method2();
}
}, "B");
t1.start();
t2.start();
}
}
由于持有不同的“”对象监视器“”，所以打印结果就是乱序的
内置类与同步：实验2
锁对象的改变
package Second;
public class MyService {
private String lock = "123";
public void testMethod() {
try {
synchronized (lock) {
System.out.println(Thread.currentThread().getName() + " begin "
+ System.currentTimeMillis());
lock = "456";
Thread.sleep(2000);
System.out.println(Thread.currentThread().getName() + " end "
+ System.currentTimeMillis());
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
package Second;
public class ThreadA extends Thread {
private MyService service;
public ThreadA(MyService service) {
super();
this.service = service;
}
@Override
public void run() {
service.testMethod();
}
}
package Second;
public class ThreadB extends Thread {
private MyService service;
public ThreadB(MyService service) {
super();
this.service = service;
}
@Override
public void run() {
service.testMethod();
}
}
package Second;
public class Run1 {
public static void main(String[] args) throws InterruptedException {
MyService service = new MyService();
ThreadA a = new ThreadA(service);
a.setName("A");
ThreadB b = new ThreadB(service);
b.setName("B");
a.start();
Thread.sleep(50);
b.start();
}
}
因为50毫秒过后线程B获得的锁时“”456“”
package Second;
public class Run2 {
public static void main(String[] args) throws InterruptedException {
MyService service = new MyService();
ThreadA a = new ThreadA(service);
a.setName("A");
ThreadB b = new ThreadB(service);
b.setName("B");
a.start();
b.start();
}
}
线程AB持有的锁都是“”123“”，虽然将锁改成了“”456“”，但结果还是同步的，因为A和B共同争抢的锁时“”123“”
package Second;
public class Userinfo {
private String username;
private String password;
public Userinfo() {
super();
}
public Userinfo(String username, String password) {
super();
this.username = username;
this.password = password;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
package Second;
public class Service {
public void serviceMethodA(Userinfo userinfo) {
synchronized (userinfo) {
try {
System.out.println(Thread.currentThread().getName());
userinfo.setUsername("abcabcabc");
Thread.sleep(3000);
System.out.println("end! time=" + System.currentTimeMillis());
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
package Second;
public class ThreadA extends Thread {
private Service service;
private Userinfo userinfo;
public ThreadA(Service service,
Userinfo userinfo) {
super();
this.service = service;
this.userinfo = userinfo;
}
@Override
public void run() {
service.serviceMethodA(userinfo);
}
}
package Second;
public class ThreadB extends Thread {
private Service service;
private Userinfo userinfo;
public ThreadB(Service service,
Userinfo userinfo) {
super();
this.service = service;
this.userinfo = userinfo;
}
@Override
public void run() {
service.serviceMethodA(userinfo);
}
}
package Second;
public class Run {
public static void main(String[] args) {
try {
Service service = new Service();
Userinfo userinfo = new Userinfo();
ThreadA a = new ThreadA(service, userinfo);
a.setName("a");
a.start();
Thread.sleep(50);
ThreadB b = new ThreadB(service, userinfo);
b.setName("b");
b.start();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
上述实验表明：只要对象不变，即使对象的属性被改变，运行的结果还是同步。
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