Java中优雅地扩展抽象父类功能：无需重写现有代码添加新日志级别

public abstract class AbstractLogger {
    public enum Levels {
        DEBUG, INFO, WARNING, ERROR
    }

    public void debug(String message) {
        log(Levels.DEBUG, message);
    }

    public void info(String message) {
        log(Levels.INFO, message);
    }

    public void warning(String message) {
        log(Levels.WARNING, message);
    }

    public void error(String message) {
        log(Levels.ERROR, message);
    }

    // 核心的日志处理方法，由子类实现具体逻辑
    public abstract void log(Levels level, String message); 
}

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.nio.file.Path;

public class FileAppenderLogger extends AbstractLogger {
    private final Path logPath;

    public FileAppenderLogger(Path logPath) {
        this.logPath = logPath;
        createLogFile();
    }

    private void createLogFile() {
        try {
            File logFile = new File(logPath.toString());
            if (logFile.createNewFile()) {
                System.out.println("File created: " + logFile.getName());
            } else {
                System.out.println("File already exists.");
            }
        } catch (IOException e) {
            System.out.println("An error occurred during file creation.");
            e.printStackTrace();
        }
    }

    @Override
    public void log(Levels level, String message) {
        try (FileWriter myWriter = new FileWriter(this.logPath.toString(), true)) { // 使用true进行追加写入
            myWriter.write("[" + level.name() + "] " + message + "\n");
            System.out.println("Successfully wrote to the file.");
        } catch (IOException e) {
            System.out.println("An error occurred during file write.");
            e.printStackTrace();
        }
    }

    // 注意：原始示例中这里的重写是错误的，会调用错误的super方法。
    // 如果子类不改变父类特定级别方法的行为，则无需重写。
    // 如果重写，应正确委托或实现新逻辑。
    /*
    @Override
    public void debug(String message) {
        super.info(message); // 错误：应为super.debug(message) 或直接log(Levels.DEBUG, message);
    }
    // ... 其他类似错误重写
    */
}

public abstract class AbstractLogger {
    public enum Levels {
        DEBUG, INFO, WARNING, ERROR, FATAL // 新增FATAL级别
    }

    // ... 现有方法不变 ...

    // 新增FATAL级别的便捷方法
    public void fatal(String message) {
        log(Levels.FATAL, message);
    }

    public abstract void log(Levels level, String message);
}

// FileAppenderLogger 无需修改，它将自动支持新的FATAL级别
public class FileAppenderLogger extends AbstractLogger {
    // ... 构造器和createLogFile方法不变 ...

    @Override
    public void log(Levels level, String message) {
        try (FileWriter myWriter = new FileWriter(this.logPath.toString(), true)) {
            // 这里会接收到Levels.FATAL，并正常处理
            myWriter.write("[" + level.name() + "] " + message + "\n");
            System.out.println("Successfully wrote to the file with level: " + level.name());
        } catch (IOException e) {
            System.out.println("An error occurred during file write.");
            e.printStackTrace();
        }
    }
}