使用Runnable實現數據共享，供大家參考，具體內容如下
先上代碼：
public class TestThread {
private static final Logger logger = LoggerFactory.getLogger(TestThread.class);
private final class MyRunnable implements Runnable {
private int i;
public MyRunnable() {
this.i = 10;
}
public void run() {
while(i > 0) {
synchronized (this) {
if (i > 0) {
i--;
logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i);
}
}
}
}
}
@Test
public void testRunable() throws InterruptedException{
MyRunnable myRunnable = new MyRunnable();
Thread th2 = new Thread(myRunnable);
Thread th3 = new Thread(myRunnable);
th2.start();
th3.start();
th2.join();
th3.join();
}
}
樓上的代碼很簡單，模擬一個售票系統。通過兩個Thread對象開啟兩條線程同時運行一個MyRunnable實例。
幾個注意點：
1. 沒有加上synchronised關鍵詞的話，即
public void run() {
while(i > 0) {
if (i > 0) {
i--;
logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i);
}
}
}
系統的運行結果：
Thread-1 buy one ticket, 8 left. Thread-2 buy one ticket, 8 left. Thread-2 buy one ticket, 6 left. Thread-1 buy one ticket, 6 left. Thread-2 buy one ticket, 5 left. Thread-1 buy one ticket, 4 left. Thread-2 buy one ticket, 3 left. Thread-1 buy one ticket, 2 left. Thread-2 buy one ticket, 1 left. Thread-1 buy one ticket, 0 left.
可以看到，缺少同步的程序輸出明顯有問題。
2. 在進入同步代碼塊之后，還需要對i的值再進行一次判斷，即，如果不加if判斷：
public void run() {
while(i > 0) {
synchronized (this) {
i--;
logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i);
}
}
}
程序的運行結果為：
Thread-2 buy one ticket, 9 left. Thread-2 buy one ticket, 8 left. Thread-2 buy one ticket, 7 left. Thread-2 buy one ticket, 6 left. Thread-2 buy one ticket, 5 left. Thread-2 buy one ticket, 4 left. Thread-2 buy one ticket, 3 left. Thread-2 buy one ticket, 2 left. Thread-2 buy one ticket, 1 left. Thread-2 buy one ticket, 0 left. Thread-1 buy one ticket, -1 left.
可以看出，出現了“多賣”的現象， 所以需要在進入同步代碼塊中再進行一次if判斷。
總結
synchronised用于互斥訪問共享變量， 并在同步代碼塊中使用if判斷更新共享變量。
以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持億速云。
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