switch()使用有关问题

class Zuoye1 {    public static void main(String[] args)     {        long str=System.currentTimeMillis();        Magicer m1=new Magicer("甘道夫",55,10,9,"B");    //定义玩家1        m1.practice();        System.out.printf("fire hurt is %d,level is %d,DPS is %d\n",m1.fire(),m1.getLevel(),m1.attack());        m1.practice();        System.out.printf("fire hurt is %d,level is %d,DPS is %d\n",m1.fire(),m1.getLevel(),m1.attack());        m1.practice();        System.out.printf("fire hurt is %d,level is %d,DPS is %d\n",m1.fire(),m1.getLevel(),m1.attack());        long end=System.currentTimeMillis();        System.out.printf("run time:%s",(end-str));    }}interface Role{    public int attack();    //攻击    public void practice();        //练习}abstract class NameRole implements Role        //角色名字和年龄{    private String name;    private int age;    public NameRole(String name,int age){        this.name=name;        this.age=age;    }}interface    MagicStick {    public int fire();}class GreenStick implements MagicStick{    private int month;    public GreenStick(int month){        this.month=month;    }    public int fire(){        if(month==6||month==7||month==8)            return 2;        else            return 1;    }}class BlackStick implements MagicStick{    private int month;    public BlackStick(int month){        this.month=month;    }    public int fire(){        if(month%2==0)            return 2;        else            return 1;    }}class Magicer extends NameRole implements MagicStick{    private String name;    private int age;    private int level;    //魔法值    private int month;            //升级月份    private String stick;    Magicer(String name,int age,int level,int month,String stick){        super(name,age);        this.level=level;        this.month=month;        this.stick=stick;    }    public int getLevel(){        return this.level;    }    public int fire(){        //使用法术        int res=0;    //返回值        switch(stick){            case "G":GreenStick s1=new GreenStick(this.month);                            res=s1.fire();                            break;            case "B":BlackStick s2=new BlackStick(this.month);                        res= s2.fire();                        break;            default:System.out.println("haven't using stick!");        }        return res;    }    public int attack(){        return this.level*5;    }    public void practice(){        if(this.stick==null)            level++;        else             level+=1+this.fire();        month++;    }    }