Java中的死鎖和活鎖都是并發(fā)編程中的常見(jiàn)問(wèn)題，它們都是由于線程間互相等待對(duì)方釋放資源而導(dǎo)致的程序無(wú)限阻塞的問(wèn)題。不過(guò)，死鎖是兩個(gè)或多個(gè)線程互相等待對(duì)方持有的資源而無(wú)法繼續(xù)執(zhí)行下去，活鎖則是線程一直重試某個(gè)操作，但由于某些原因一直失敗而無(wú)法終止。

public class DeadlockExample {
static Object lock1 = new Object();
static Object lock2 = new Object();
public static void main(String[] args) {
Thread thread1 = new Thread(() ->{
synchronized (lock1) {
System.out.println("Thread 1 acquired lock 1");
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (lock2) {
System.out.println("Thread 1 acquired lock 2");
}
}
});
Thread thread2 = new Thread(() ->{
synchronized (lock2) {
System.out.println("Thread 2 acquired lock 2");
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (lock1) {
System.out.println("Thread 2 acquired lock 1");
}
}
});
thread1.start();
thread2.start();
}
}

上面是一個(gè)經(jīng)典的死鎖示例，兩個(gè)線程相互占用對(duì)方需要的鎖，然后進(jìn)入無(wú)限等待狀態(tài)。如果在實(shí)際應(yīng)用中發(fā)生了這種情況，程序就會(huì)一直阻塞下去，導(dǎo)致資源浪費(fèi)和性能下降。

public class LivelockExample {
static Integer count = 0;
public static void main(String[] args) {
Thread thread1 = new Thread(() ->{
while (count< 5) {
count++;
System.out.println("Thread 1 increments count to " + count);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
Thread thread2 = new Thread(() ->{
while (count >0) {
count--;
System.out.println("Thread 2 decrements count to " + count);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
thread1.start();
thread2.start();
}
}

這是一個(gè)簡(jiǎn)單的活鎖示例，兩個(gè)線程都在不停地嘗試修改一個(gè)共享變量count，由于兩個(gè)線程互相干擾，它們一直無(wú)法正確地完成操作，最終導(dǎo)致程序一直運(yùn)行下去。這種情況很類似于兩個(gè)人在走廊上面試讓對(duì)方讓路，但彼此都不愿意離開(kāi)，最終導(dǎo)致雙方都無(wú)法通過(guò)。