JAVA存取對象屬性時，如果開程多線程，記得對相關存取方法作原子化操作定義

標籤：

最顯著的應用當然是銀行存款和取款，不要存在存取數字和實際發生不一樣的情況。

synchronized關鍵字。

class BankAccount {    private int balance = 100;    public int getBalance() {        return balance;    }    public void withdraw(int amount) {        balance = balance - amount;    }}public class RyanAndMonicaJob implements Runnable {    private BankAccount account = new BankAccount();    public static void main(String[] args) {        // TODO Auto-generated method stub        RyanAndMonicaJob theJob = new RyanAndMonicaJob();        Thread one = new Thread(theJob);        Thread two = new Thread(theJob);        one.setName("Ryan");        two.setName("Monica");        one.start();        two.start();    }    public void run() {        for (int x = 0; x < 10; x++) {            makeWithdrawal(10);            if (account.getBalance() < 0) {                System.out.println("Overdrawn!");            }        }    }    private synchronized void makeWithdrawal(int amount) {        if (account.getBalance() >= amount) {            System.out.println(Thread.currentThread().getName() + " is about to withdraw");            try {                System.out.println(Thread.currentThread().getName() + " is going to sleep");                Thread.sleep(500);            } catch (InterruptedException ex) {                ex.printStackTrace();            }            System.out.println(Thread.currentThread().getName() + " woke up.");            account.withdraw(amount);            System.out.println(Thread.currentThread().getName() + " completes the withdrawl");        } else {            System.out.println("Sorry, not enough for " + Thread.currentThread().getName());        }            }}

Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica

JAVA存取對象屬性時，如果開程多線程，記得對相關存取方法作原子化操作定義