命令模式(Command Pattern)属于行为型模式。请求以命令的形式包裹在对象中,并传给调用对象。调用对象寻找可以处理该命令的合适的对象,并把该命令传给相应的对象,该对象执行命令,执行顺序是调用者→命令→接收者,实现调用者(Invoker)与接收者(Receiver)解耦
设计一个文本编辑器(TextField),支持复制、插入以及撤销操作
业务代码
//抽象命令 public interface Command { void execute(); void undo(); } //调用者 class Invoker{ private Command command; public Invoker(Command command) { this.command = command; } public void setCommand(Command command) { this.command = command; } public void call(){ command.execute(); command.undo(); } } //具体命令 class insertCommand implements Command { private TextField textField; private String insertStr = "insertStr"; public insertCommand(TextField textField) { this.textField = textField; } @Override public void execute() { textField.text += insertStr; System.out.println(textField.text); } @Override public void undo() { textField.text = textField.text.substring(0, textField.text.length() - insertStr.length()); System.out.println(textField.text); } } //具体命令 class CopyCommand implements Command { private TextField textField; public CopyCommand(TextField textField) { this.textField = textField; } @Override public void execute() { textField.text += textField.text; System.out.println(textField.text); } @Override public void undo() { textField.text = textField.text.substring(0, textField.text.length() / 2); System.out.println(textField.text); } } //接收者 class TextField { public String text = "text"; }
客户端
public class Client { public static void main(String[] args) { Invoker invoker = new Invoker(new CopyCommand(new TextField())); invoker.call(); } }
优点
java.lang.Runnable是一个典型的命令模式,Runnable充当抽象命令的角色,Thread充当调用者的角色,而接收者的角色是开发者自己定义的
//具体命令 class ConcreteCommand implements Runnable{ private Receiver receiver; public ConcreteCommand(Receiver receiver) { this.receiver = receiver; } @Override public void run() { receiver.execute(); } } //接收者 class Receiver{ public void execute(){ System.out.println("执行逻辑"); } }