Share an example tutorial on the basics of Java multithreading

public class Test {

    static class ThreadOne extends Thread {

        private Callback mCallback;

        @Override
        public void run() {
            work();
            if (mCallback != null) {
                mCallback.onResult(false);
            }
        }

        // 耗时 3s
        private void work() {
            System.out.println(" 正在查询数据库 1");
            long startTime = System.currentTimeMillis();
            while (true) {
                if (System.currentTimeMillis() - startTime < 3000) {
                    continue;
                }
                break;
            }
        }

        public void setCallback(Callback callback) {
            mCallback = callback;
        }

        public interface Callback {
            void onResult(boolean result);
        }
    }

    static class ThreadTest extends Thread {

        private Object mLock = new Object();

        private ThreadOne mThreadOne;

        @Override
        public void run() {
            workOne();
            System.out.println(" 根据结果继续做其他事情 ");
        }

        private void workOne() {
            mThreadOne = new ThreadOne();
            mThreadOne.setCallback(new ThreadOne.Callback() {
                @Override
                public void onResult(boolean result) {
                    System.out.println(" 查询数据库 1 结束，:" + (result ? " 有数据 " : " 无数据 "));
                    synchronized (mLock) {
                        mLock.notify();
                        System.out.println("--ThreadTest 结束等待 --");
                    }
                }
            });
            mThreadOne.start();
            try {
                synchronized (mLock) {
                    System.out.println("--ThreadTest 进入等待 --");
                    mLock.wait();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] var0) {
        ThreadTest threadTest = new ThreadTest();
        threadTest.start();
    }
}

--ThreadTest 进入等待--
正在查询数据库 1
查询数据库 1 结束，: 无数据
--ThreadTest 结束等待--
根据结果继续做其他事情

public class Test {

    private static Object mLock = new Object();

    static class MyThread extends Thread {

        String mName;
        Callback mCallback;

        public MyThread(String name){
            mName = name;
        }

        @Override
        public void run() {
            work();
            if (mCallback != null) {
                mCallback.onResult(false);
            }
        }

        // 耗时 3s
        private void work() {
            System.out.println(mName + " 等待 ");
            try {
                synchronized (mLock) {
                    mLock.wait();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        public void setCallback(Callback callback) {
            mCallback = callback;
        }

        public interface Callback {
            void onResult(boolean result);
        }
    }

    static class ThreadTest extends Thread {



        @Override
        public void run() {
            work("db1");
            work("db2");
            work("db3");

            try {
                sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            synchronized (mLock) {
                System.out.println(" 唤醒全部 ");
                mLock.notifyAll();
            }
        }

        private void work(String name) {
            final MyThread myThread = new MyThread(name);
            myThread.setCallback(new MyThread.Callback() {
                @Override
                public void onResult(boolean result) {
                    System.out.println(myThread.mName + " 回来了 ");
                }
            });
            myThread.start();
        }
    }

    public static void main(String[] var0) {
        ThreadTest threadTest = new ThreadTest();
        threadTest.start();
    }
}

db1 等待
db3 等待
db2 等待
唤醒全部
db3 回来了
db1 回来了
db2 回来了