1。检查线程是否完成的方法：
isalive()
- 如果线程仍在运行则返回true；否则，返回 false。
- 用于持续检查线程的状态。
加入()
- 使调用该方法的线程等待，直到指定线程完成。
- 有多种变体允许您定义最长等待时间。
2。使用 isalive() 的示例：
// verifica se as threads estão vivas
class mythread implements runnable {
thread thrd;
mythread(string name) {
thrd = new thread(this, name);
thrd.start(); // inicia a thread
}
public void run() {
system.out.println(thrd.getname() + " starting.");
try {
for (int count = 0; count < 10; count++) {
thread.sleep(400); // suspende a execução por 400ms
system.out.println("in " + thrd.getname() + ", count is " + count);
}
} catch (interruptedexception exc) {
system.out.println(thrd.getname() + " interrupted.");
}
system.out.println(thrd.getname() + " terminating.");
}
}
class morethreads {
public static void main(string[] args) {
system.out.println("main thread starting.");
mythread mt1 = new mythread("child #1");
mythread mt2 = new mythread("child #2");
mythread mt3 = new mythread("child #3");
// verifica se as threads ainda estão vivas
do {
system.out.print(".");
try {
thread.sleep(100);
} catch (interruptedexception exc) {
system.out.println("main thread interrupted.");
}
} while (mt1.thrd.isalive() || mt2.thrd.isalive() || mt3.thrd.isalive());
system.out.println("main thread ending.");
}
}
重要要点：
- 主线程不断检查 isalive() 直到所有子线程都完成。
- 线程的执行是由 java 调度的，因此确切的输出可能会有所不同。
3。使用 join() 的示例：
// aguarda o término das threads com join()
class mythread implements runnable {
thread thrd;
mythread(string name) {
thrd = new thread(this, name);
thrd.start(); // inicia a thread
}
public void run() {
system.out.println(thrd.getname() + " starting.");
try {
for (int count = 0; count < 10; count++) {
thread.sleep(400); // suspende a execução por 400ms
system.out.println("in " + thrd.getname() + ", count is " + count);
}
} catch (interruptedexception exc) {
system.out.println(thrd.getname() + " interrupted.");
}
system.out.println(thrd.getname() + " terminating.");
}
}
class jointhreads {
public static void main(string[] args) {
system.out.println("main thread starting.");
mythread mt1 = new mythread("child #1");
mythread mt2 = new mythread("child #2");
mythread mt3 = new mythread("child #3");
try {
mt1.thrd.join(); // aguarda child #1 terminar
system.out.println("child #1 joined.");
mt2.thrd.join(); // aguarda child #2 terminar
system.out.println("child #2 joined.");
mt3.thrd.join(); // aguarda child #3 terminar
system.out.println("child #3 joined.");
} catch (interruptedexception exc) {
system.out.println("main thread interrupted.");
}
system.out.println("main thread ending.");
}
}
预期输出（可能会有所不同）：
Main thread starting. Child #1 starting. Child #2 starting. Child #3 starting. In Child #1, count is 0 In Child #2, count is 0 In Child #3, count is 0 ... Child #1 terminating. Child #1 joined. Child #2 terminating. Child #2 joined. Child #3 terminating. Child #3 joined. Main thread ending.
重要要点：
- join() 确保主线程仅在子线程完成后继续。
- 输出显示每个线程按预期顺序终止。
