两个线程一个输出字母，一个输出数字，交替输出A1B2C3D4E5F6G7。

第一种方式：

import java.util.concurrent.CountDownLatch;

public class ConcurrentTest {
    private static CountDownLatch latch= new CountDownLatch(1);

    public static void main(String[] args) {
        final Object o = new Object();
        char[] number = "1234567".toCharArray();
        char[] letter = "ABCDEFG".toCharArray();
        new Thread(() -> {
            try {
                latch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized (o) {
                for (char c : number) {
                    System.out.print(c);
                    try {
                        o.notify();
                        o.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                o.notify();
            }
        }, "t1").start();

        new Thread(() -> {
            synchronized (o) {
                for (char c : letter) {
                    System.out.print(c);
                    latch.countDown();
                    try {
                        o.notify();
                        o.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                o.notify();
            }
        }, "t2").start();
    }
}

第二种方式：

import java.util.concurrent.CountDownLatch;

public class ConcurrentTest {
    private static volatile boolean task = false;

    public static void main(String[] args) {
        final Object o = new Object();
        char[] number = "1234567".toCharArray();
        char[] letter = "ABCDEFG".toCharArray();
        new Thread(() -> {
            synchronized (o) {
                while (!task) {
                    try {
                        o.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                for (char c : number) {
                    System.out.print(c);
                    try {
                        o.notify();
                        o.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                o.notify();
            }
        }, "t1").start();

        new Thread(() -> {
            synchronized (o) {
                for (char c : letter) {
                    System.out.print(c);
                    task = true;
                    try {
                        o.notify();
                        o.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                o.notify();
            }
        }, "t2").start();
    }
}

第三种方式：

import java.util.concurrent.locks.LockSupport;

public class ConcurrentTest {
    static Thread t1 = null, t2 = null;

    public static void main(String[] args) {
        char[] number = "1234567".toCharArray();
        char[] letter = "ABCDEFG".toCharArray();
        t1 = new Thread(() -> {
            for (char c : number) {
                LockSupport.park();
                System.out.print(c);
                LockSupport.unpark(t2);

            }
        }, "t1");

        t2 = new Thread(() -> {
            for (char c : letter) {
                System.out.print(c);
                LockSupport.unpark(t1);
                LockSupport.park();
            }
        }, "t2");
        t1.start();
        t2.start();
    }
}

第四种方式：

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class ConcurrentTest {
    public static void main(String[] args) {
        char[] number = "1234567".toCharArray();
        char[] letter = "ABCDEFG".toCharArray();
        Lock lock = new ReentrantLock();
        Condition condition1 = lock.newCondition();
        Condition condition2 = lock.newCondition();
        new Thread(() -> {
            try {
                lock.lock();
                condition1.await();
                for (char c : number) {
                    System.out.print(c);
                    condition2.signal();
                    condition1.await();
                }
                condition2.signal();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }, "t1").start();

        new Thread(() -> {
            try {
                lock.lock();
                for (char c : letter) {
                    System.out.print(c);
                    condition1.signal();
                    condition2.await();
                }
                condition1.signal();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }, "t2").start();

    }
}