用Java实现

好的，下面是用 Java 实现的代码：

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

class Pond {
    private int capacity;
    private int currentWaterLevel;
    private Lock lock;

    public Pond(int capacity) {
        this.capacity = capacity;
        this.currentWaterLevel = 0;
        this.lock = new ReentrantLock();
    }

    public void injectWater(int amount) {
        lock.lock();
        if (isFull()) {
            System.out.println("Water pond is already full!");
        } else {
            currentWaterLevel += amount;
            System.out.println("Injected " + amount + " units of water into the pond. Current water level: " + currentWaterLevel);
        }
        lock.unlock();
    }

    public void drainWater(int amount) {
        lock.lock();
        if (isEmpty()) {
            System.out.println("Water pond is already empty!");
        } else {
            currentWaterLevel -= amount;
            System.out.println("Drained " + amount + " units of water from the pond. Current water level: " + currentWaterLevel);
        }
        lock.unlock();
    }

    public boolean isFull() {
        return currentWaterLevel == capacity;
    }

    public boolean isEmpty() {
        return currentWaterLevel == 0;
    }
}

class Injection extends Thread {
    private Pond pond;
    private int amount;

    public Injection(Pond pond, int amount) {
        this.pond = pond;
        this.amount = amount;
    }

    public void run() {
        pond.injectWater(amount);
    }
}

class Drain extends Thread {
    private Pond pond;
    private int amount;

    public Drain(Pond pond, int amount) {
        this.pond = pond;
        this.amount = amount;
    }

    public void run() {
        pond.drainWater(amount);
    }
}

public class Main {
    public static void main(String[] args) {
        Pond pond = new Pond(100);
        Injection injection = new Injection(pond, 50);
        Drain drain = new Drain(pond, 25);

        injection.start();
        drain.start();

        try {
            injection.join();
            drain.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

在 Java 中，我们使用了 `java.util.concurrent.locks.Lock` 接口和 `java.util.concurrent.locks.ReentrantLock` 类来实现线程同步。和 Python 版本类似，我们在 `injectWater()` 和 `drainWater()` 方法中获取锁，确保同一时间只有一个线程可以修改水塘的水位高度。由于 Java 中的锁需要手动释放，我们在 `lock()` 方法之后使用了 `unlock()` 方法释放锁。

最后，我们在 `main()` 方法中创建一个 `Pond` 对象，然后创建一个注水线程和一个排水线程，分别进行注水和排水操作。我们还使用了 `join()` 方法等待线程执行完毕。