代码如下：

public class MobilPhone {
    public String brand;
    public MobilPhone(){
        this.brand="诺基亚";
    }
    public MobilPhone(String bra){
        this.brand=bra;
    }
    public String buy(){
        return "没发工资， 买一个"+brand+"牌子的手机吧";
    }
    public String Buy(String reason){
        return reason + "，快买一个" + brand + "牌子的手机吧！";
    }
}

public class MobilPhoneTest {
    public static void main(String[] args){
        MobilPhone mp = new MobilPhone();
        mp.brand="苹果";						//发工资了,修改品牌属性
        String detail=mp.Buy("发工资啦");		//发工资了,调用带参构造方法
        System.out.println(detail);
    }
}