Java 状态模式：模拟 TCP 连接多种状态及行为转换

```java // TCPConnectionState 接口定义了TCP连接状态的行为 interface TCPConnectionState { void open(); // 建立连接 void close(); // 关闭连接 void listen(); // 监听连接 } // EstablishedState 表示TCP连接已建立状态 class EstablishedState implements TCPConnectionState { @Override public void open() { System.out.println("Connection is already established."); } @Override public void close() { System.out.println("Closing the connection."); } @Override public void listen() { System.out.println("Connection is established and listening for data."); } } // ListeningState 表示TCP连接正在监听状态 class ListeningState implements TCPConnectionState { @Override public void open() { System.out.println("Connection is already listening."); } @Override public void close() { System.out.println("Closing the connection."); } @Override public void listen() { System.out.println("Connection is already listening."); } } // ClosedState 表示TCP连接已关闭状态 class ClosedState implements TCPConnectionState { @Override public void open() { System.out.println("Connection is closed. Cannot open a closed connection."); } @Override public void close() { System.out.println("Connection is already closed."); } @Override public void listen() { System.out.println("Connection is closed. Cannot listen on a closed connection."); } } // TCPConnection 类代表TCP连接对象 class TCPConnection { private TCPConnectionState state; // 初始状态为已关闭 public TCPConnection() { this.state = new ClosedState(); } public void setState(TCPConnectionState state) { this.state = state; } // 建立连接 public void open() { state.open(); } // 关闭连接 public void close() { state.close(); } // 监听连接 public void listen() { state.listen(); } } // 测试类 public class Main { public static void main(String[] args) { TCPConnection connection = new TCPConnection(); // 初始状态为已关闭 connection.open(); // Connection is already established. connection.setState(new EstablishedState()); // 切换到已建立状态 connection.open(); // Connection is already established. connection.listen(); // Connection is established and listening for data. connection.setState(new ListeningState()); // 切换到监听状态 connection.listen(); // Connection is already listening. connection.setState(new ClosedState()); // 切换到关闭状态 connection.close(); // Connection is already closed. connection.listen(); // Connection is closed. Cannot listen on a closed connection. } } ``` 额外注意的地方： 1. 状态模式中的每个状态类都实现了 `TCPConnectionState` 接口，确保了不同状态下有不同的行为。 2. 在 `TCPConnection` 类中，通过 `setState` 方法可以动态改变连接对象的状态，实现了状态的转换。 3. 测试类 `Main` 中展示了连接对象在不同状态下的行为表现，验证了状态模式的有效性。 ######[AI写代码神器 | 2147点数解答 | 2024-12-19 22:19:37]