public class JoinBasicDemo {
    public static void main(String[] args) {
        // 定義子線程：模擬耗時任務(wù)（打印1-5，每次間隔500ms）
        Thread subThread = new Thread(() -> {
            for (int i = 1; i <= 5; i++) {
                try {
                    Thread.sleep(500); // 模擬任務(wù)耗時
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("子線程執(zhí)行中：i = " + i);
            }
            System.out.println("子線程執(zhí)行完畢！");
        }, "子線程-Test");

        System.out.println("主線程啟動子線程...");
        subThread.start(); // 啟動子線程

        try {
            System.out.println("主線程開始等待子線程執(zhí)行完畢...");
            subThread.join(); // 主線程阻塞，等待subThread執(zhí)行完
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        // 子線程執(zhí)行完后，主線程才會執(zhí)行這里
        System.out.println("主線程繼續(xù)執(zhí)行，程序結(jié)束！");
    }
}

主線程啟動子線程...
主線程開始等待子線程執(zhí)行完畢...
子線程執(zhí)行中：i = 1
子線程執(zhí)行中：i = 2
子線程執(zhí)行中：i = 3
子線程執(zhí)行中：i = 4
子線程執(zhí)行中：i = 5
子線程執(zhí)行完畢！
主線程繼續(xù)執(zhí)行，程序結(jié)束！

public class JoinTimeoutDemo {
    public static void main(String[] args) {
        Thread subThread = new Thread(() -> {
            for (int i = 1; i <= 5; i++) {
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("子線程執(zhí)行中：i = " + i);
            }
            System.out.println("子線程執(zhí)行完畢！");
        }, "子線程-Timeout");

        System.out.println("主線程啟動子線程...");
        subThread.start();

        try {
            System.out.println("主線程開始等待子線程（超時1500ms）...");
            subThread.join(1500); // 最多等待1500ms
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        // 1500ms后，主線程不再等待，直接執(zhí)行后續(xù)代碼
        System.out.println("主線程等待超時，繼續(xù)執(zhí)行自身邏輯！");
    }
}

主線程啟動子線程...
主線程開始等待子線程（超時1500ms）...
子線程執(zhí)行中：i = 1
子線程執(zhí)行中：i = 2
子線程執(zhí)行中：i = 3
主線程等待超時，繼續(xù)執(zhí)行自身邏輯！
子線程執(zhí)行中：i = 4
子線程執(zhí)行中：i = 5
子線程執(zhí)行完畢！

public class JoinSerialDemo {
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(() -> {
            for (int i = 1; i <= 3; i++) {
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("線程t1執(zhí)行中：i = " + i);
            }
        }, "線程t1");

        Thread t2 = new Thread(() -> {
            for (int i = 1; i <= 3; i++) {
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("線程t2執(zhí)行中：i = " + i);
            }
        }, "線程t2");

        t1.start();
        t1.join(); // 主線程先等t1執(zhí)行完
        t2.start();
        t2.join(); // 再等t2執(zhí)行完

        System.out.println("所有子線程執(zhí)行完畢，主線程結(jié)束！");
    }
}

public class JoinParallelDemo {
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(() -> {
            for (int i = 1; i <= 3; i++) {
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("線程t1執(zhí)行中：i = " + i);
            }
        }, "線程t1");

        Thread t2 = new Thread(() -> {
            for (int i = 1; i <= 3; i++) {
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("線程t2執(zhí)行中：i = " + i);
            }
        }, "線程t2");

        // 先同時啟動兩個子線程
        t1.start();
        t2.start();

        // 主線程同時等待兩個子線程（誰先執(zhí)行完誰先喚醒，最終等待耗時為較慢線程的執(zhí)行時間）
        t1.join();
        t2.join();

        System.out.println("所有子線程執(zhí)行完畢，主線程結(jié)束！");
    }
}

// 無參join() 等價(jià)于 join(0)
public final void join() throws InterruptedException {
    join(0);
}

// 帶毫秒?yún)?shù)的核心實(shí)現(xiàn)
public final synchronized void join(long millis) throws InterruptedException {
    long base = System.currentTimeMillis();
    long now = 0;

    if (millis < 0) {
        throw new IllegalArgumentException("timeout value is negative");
    }

    // millis=0 表示無限等待
    if (millis == 0) {
        // 只要目標(biāo)線程還存活，調(diào)用線程就一直wait
        while (isAlive()) {
            wait(0);
        }
    } else {
        // 超時等待邏輯：循環(huán)判斷，避免虛假喚醒
        while (isAlive()) {
            long delay = millis - now;
            if (delay <= 0) {
                break;
            }
            wait(delay);
            now = System.currentTimeMillis() - base;
        }
    }
}