Command_Pattern

package command_pattern;

public abstract class Command {
    protected Receiver receiver;
    public Command(Receiver receiver) {
        this.receiver = receiver;
    }
    public abstract void executed();
}

package command_pattern;

public class ConcreteCommand extends Command{
    public ConcreteCommand(Receiver receiver) {
        super(receiver);
    }
    @Override
    public void executed() {
        receiver.action();//Give the command to receiver.
    }
}

package command_pattern;

public class Receiver {
    public void action() {
        System.out.println("Executed the request.");
    }
}

package command_pattern;

public class Invoker {
    private Command command;//It can gather a set of commands to execute together
    //through using ArrayList<T>.
    public void setCommand(Command command) {
        this.command = command;
    }
    public void executedCommand() {
        command.executed();
    }
}

package command_pattern;

public class Main {
    public static void main(String args[]) {
        Receiver r = new Receiver();
        Command c = new ConcreteCommand(r);//Map the command and receiver together.
        Invoker i = new Invoker();
        i.setCommand(c);//Invoker composites the command so as to invoke different
        //command.The super class command composite the receiver so as to send the
        //command to the related receiver.
        i.executedCommand();
    }
}
This is a general introduction to the 23 design patterns：
https://blog.youkuaiyun.com/GZHarryAnonymous/article/details/81567214

See more source code:[GZHarryAnonymous](https://github.com/GZHarryAnonymous/Design_Pattern)