java之 ------ 多线程（交互线程）

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1、运行结果不惟一，取决于线程调度
2、线程执行被打断时出现错误

3、线程互斥和临界区管理

1）操作系统对共享一个变量的若干线程进入各自临界区有以下3个调度原则：
2）一次至多一个线程能够在它的临界区内。
3）不能让一个线程无限地留在它的临界区内。
4）不能强迫一个线程无限地等待进入它的临界区。特别地，进入临界区的任一线程不能妨碍正等待进入的其他线程的进展。

4、同步语句 synchronized (对象)

同步方法 synchronized 方法声明方法声明synchronized(this){ 方法体 }

5、银行账户的存款取款线程

Account.c

package p25;public class Account {private String name;//储户姓名private double balance;//账户余额public Account(String name) {this.name = name;this.balance = 0;}//查询余额public double balance() {return this.balance;}public String getName() {return this.name;}//存款操作public void put(double value) {if (value > 0) {this.balance += value;}}//取款操作public double get(double value) {if (value > 0) {if (value < this.balance) {//够取this.balance -= value;} else {value = this.balance;this.balance = 0;}return value;}return 0;}}class Save extends Thread {private Account account;private double value;public Save(Account account, double value) {this.account = account;this.value = value;}public void run() {synchronized (account) {//声明临界区，锁定当前account对象double howmuch = this.account.balance();//查看账户余额try {sleep(1);} catch (InterruptedException e) {e.printStackTrace();}this.account.put(this.value);double howmuch2 = this.account.balance();//查看账户余额System.out.println(this.account.getName() + "账户: 现有" + howmuch+ ",存入" + this.value + ",余额为" + howmuch2);}}}class Fetch extends Thread {private Account account;private double value;public Fetch(Account account, double value) {this.account = account;this.value = value;}public void run() {synchronized (account) {double howmuch = this.account.balance();try {sleep(1);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}double v = this.account.get(this.value);double howmuch2 = this.account.balance();System.out.println(this.account.getName() + "账户: 现有" + howmuch+ ",取出" + v + ",余额为" + howmuch2);}}}class Func extends Thread {private Account account;private double value;public Func(Account account, double value) {this.account = account;this.value = value;}public void run() {fun();}synchronized void fun(){double howmuch = this.account.balance();try {sleep(1);} catch (InterruptedException e) {e.printStackTrace();}this.account.put(this.value);double v = this.account.get(this.value);double howmuch2 = this.account.balance();System.out.println(this.account.getName() + "账户: 现有" + howmuch + ",取出"+ v + ",余额为" + howmuch2);}}

Bank.c

package p25;public class Bank {public static void main(String[] args) {Account wang = new Account("wang");(new Save(wang,100)).start();(new Save(wang,200)).start();(new Fetch(wang,100)).start();Account li=new Account("li");(new Save(li,300)).start();Account xu=new Account("xu");(new Func(xu,100000)).start();}}

注：必须要声明临界区，锁定account对象，不然会出错
正确结果：

错误结果：

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