在Java中，IO和多線程是非常重要的知識點，下面是一個簡單的快遞柜程序的代碼實現。

import java.util.ArrayList;
import java.util.List;
public class ExpressBox {
public static void main(String[] args) {
ListpackageList = new ArrayList<>();
for (int i = 1; i<= 20; i++) {
packageList.add("package" + i);
}
Thread senderThread = new Thread(new Sender(packageList));
senderThread.start();
Thread receiverThread = new Thread(new Receiver(packageList));
receiverThread.start();
}
static class Sender implements Runnable {
private ListpackageList;
public Sender(ListpackageList) {
this.packageList = packageList;
}
@Override
public void run() {
synchronized (packageList) {
while (packageList.size() >0) {
try {
packageList.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
for (int i = 1; i<= 20; i++) {
String pkg = "package" + i;
packageList.add(pkg);
System.out.println("Sender: package" + i + " has been sent to the box.");
packageList.notify();
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
static class Receiver implements Runnable {
private ListpackageList;
public Receiver(ListpackageList) {
this.packageList = packageList;
}
@Override
public void run() {
synchronized (packageList) {
while (packageList.size()< 20) {
try {
packageList.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
for (int i = 1; i<= 20; i++) {
String pkg = packageList.get(i - 1);
packageList.remove(pkg);
System.out.println("Receiver: " + pkg + " has been picked up from the box.");
packageList.notify();
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
}

在這個程序中，我們使用了兩個線程，一個代表快遞員將包裹放到快遞柜里，另一個代表用戶從快遞柜里取出自己的包裹。

通過使用線程同步和wait/notify方法，我們實現了快遞員和用戶之間的交互，讓快遞柜的使用更加順暢。

IO和多線程是Java中非常重要的知識點，它們可以幫助我們處理各種復雜的任務和并發場景。