Java是一門(mén)強(qiáng)類(lèi)型、面向?qū)ο蟆⒖缙脚_(tái)的編程語(yǔ)言，被廣泛運(yùn)用于各種類(lèi)型的應(yīng)用開(kāi)發(fā)中。然而，在Java編程時(shí)，我們常常會(huì)遇到死鎖和活鎖等問(wèn)題，這些問(wèn)題可能導(dǎo)致應(yīng)用程序的運(yùn)行出現(xiàn)異常。

死鎖

public class DeadLockDemo {
private static final Object RESOURCE_A = new Object();
private static final Object RESOURCE_B = new Object();
public static void main(String[] args) {
Thread thread1 = new Thread(() -> {
synchronized (RESOURCE_A) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (RESOURCE_B) {
System.out.println("Thread-1 acquired lock on RESOURCE_B");
}
}
});
Thread thread2 = new Thread(() -> {
synchronized (RESOURCE_B) {
synchronized (RESOURCE_A) {
System.out.println("Thread-2 acquired lock on RESOURCE_A");
}
}
});
thread1.start();
thread2.start();
}
}

上面的代碼中，我們定義了兩個(gè)資源RESOURCE_A和RESOURCE_B，然后定義了兩個(gè)線程thread1和thread2。在thread1里先獲得RESOURCE_A的鎖，等待1秒后再去獲得RESOURCE_B的鎖。 而在thread2里先獲得RESOURCE_B的鎖，再去獲得RESOURCE_A的鎖。由于兩個(gè)線程持有了對(duì)方所需的鎖，因此它們會(huì)發(fā)生死鎖，程序無(wú)法正常運(yùn)行。

活鎖

public class LiveLockDemo {
private static final AtomicInteger COUNTER = new AtomicInteger(0);
public static void main(String[] args) {
Thread thread1 = new Thread(() -> {
while (COUNTER.get() < 10) {
System.out.println("Thread-1 is waiting..");
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
if (COUNTER.get() % 2 == 0) {
COUNTER.getAndIncrement();
}
}
});
Thread thread2 = new Thread(() -> {
while (COUNTER.get() < 10) {
System.out.println("Thread-2 is waiting..");
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
if (COUNTER.get() % 2 != 0) {
COUNTER.getAndIncrement();
}
}
});
thread1.start();
thread2.start();
}
}

上面的代碼中，我們定義了一個(gè)計(jì)數(shù)器COUNTER，然后定義了兩個(gè)線程thread1和thread2。thread1會(huì)增加計(jì)數(shù)器的值，但只會(huì)在計(jì)數(shù)器的值為偶數(shù)時(shí)才增加。而thread2也會(huì)增加計(jì)數(shù)器的值，但只會(huì)在計(jì)數(shù)器的值為奇數(shù)時(shí)才增加。由于兩個(gè)線程都需要同時(shí)滿足自己的條件才能增加計(jì)數(shù)器的值，因此它們可能會(huì)一直在滿足對(duì)方的條件而無(wú)法增加計(jì)數(shù)器的值，這就是活鎖。