作用

将“请求”封装成对象，以便使用不同的请求

解决应用程序中对象的职责以及它们之间的通信方式

请求调用者和接受者解耦

Demo设计

根据课程视频执行命令，比如播放 关闭

命令接口

只有一个执行方法

public interface Command {
    void execute();
}

用于被执行命令的实体类

课程视频类，提供两个方法视频开放，视频关闭，供命令类执行

public class CourseVideo {
    private String name;
    public CourseVideo(String name) {
        this.name = name;
    }
    public void open() {
        System.out.println(this.name + "视频开放");
    }
    public void close() {
        System.out.println(this.name + "视频关闭");
    }
}

命令实现类

根据课程视频创建两个类，都要实现命令接口

视频开放类

public class OpenCourseVideoCommand implements Command {
    private CourseVideo courseVideo;
    public OpenCourseVideoCommand(CourseVideo courseVideo) {
        this.courseVideo = courseVideo;
    }
    @Override
    public void execute() {
        courseVideo.open();
    }
}

视频关闭类

public class CloseCourseVideoCommand implements Command {
    private CourseVideo courseVideo;
    public CloseCourseVideoCommand(CourseVideo courseVideo) {
        this.courseVideo = courseVideo;
    }
    @Override
    public void execute() {
        courseVideo.close();
    }
}

管理命令类

用于保存命令，并根据存放命令的顺序来执行，实现命令接口的类都可以存放

public class Staff {
    private List<Command> commands = new ArrayList<>();
    public void addCommand(Command command) {
        commands.add(command);
    }
    public void executeCommands() {
        commands.forEach(Command::execute);
    }
}

测试

根据存放命令的顺序来执行

public static void main(String[] args) {
    CourseVideo courseVideo = new CourseVideo("设计模式");
    OpenCourseVideoCommand openCourseVideoCommand = new OpenCourseVideoCommand(courseVideo);
    CloseCourseVideoCommand closeCourseVideoCommand = new CloseCourseVideoCommand(courseVideo);
    Staff staff = new Staff();
    //存放命令
    staff.addCommand(openCourseVideoCommand);
    staff.addCommand(closeCourseVideoCommand);
    staff.addCommand(openCourseVideoCommand);
    staff.addCommand(closeCourseVideoCommand);
    //批量执行命令
    staff.executeCommands();
}

小结

每新增一个命令就需要新建一个实现命令接口的类