命令模式

命令模式共有4个角色： Command, ConcurrentCommand, Reciever, Invoker

Command : 抽象命令类， 定义了Reciver成员和抽象方法executeCommand()用于执行命令

ConcurrentCommand : 具体实现命令类， 继承自Command类并实现了抽象方法executeCommand()

Reciver : 实际命令执行者， executeCommand()所产生的行为由Reciever实现

Invoker : 定义了Command成员，是Command的调用者

命令模式的优点是命令记录/撤销功能，可以批次执行命令，并且命令的产生与执行解耦，生成新的命令不需要修改源代码

package command;

public abstract class Command {
    protected Reciever reciever;
    
    protected Command(Reciever reciever) {
        this.reciever = reciever;
    }
    
    public abstract void executeCommand();
}

package command;

public class ConcurrentCommand1 extends Command {
    protected ConcurrentCommand1(Reciever reciever) {
        super(reciever);
    }

    @Override
    public void executeCommand() {    // 如果需要撤销命令，则在此处插入判断条件，达成条件是撤销命令执行
        reciever.action();
        System.out.println("command1 executed");
    }
}

package command;

public class ConcurrentCommand2 extends Command {
    protected ConcurrentCommand2(Reciever reciever) {
        super(reciever);
    }

    @Override
    public void executeCommand() {
        reciever.action();
        System.out.println("command2 executed");
    }
}

package command;

public class Reciever {
    private String name;
    
    public Reciever(String name) {
        this.name = name;
    }
    
    public void action() {
        System.out.println("I'm " + name + ". Let me do it!");
    }
}

package command;

public class Invoker {
    public Command command;  // 如果需要批量执行命令，则在此处将command变为command数组，最后在使用for执行命令
    
    public void setCommand(Command command) {
        this.command = command;
    }
    
    public void executeCommand() {
        command.executeCommand();
    }
}

package command;

public class Test {
    public static void main(String[] args) {
        Reciever reciever = new Reciever("Jack");
        Command command1 = new ConcurrentCommand1(reciever);
        Command command2 = new ConcurrentCommand2(reciever);
        Invoker invoker = new Invoker();
        invoker.setCommand(command1);
        invoker.executeCommand();
        invoker.setCommand(command2);
        invoker.executeCommand();
    }
}

// ...

程序输出

I'm Jack. Let me do it!
command1 executed
I'm Jack. Let me do it!
command2 executed