练习作业

public class Phone {
    private String name;
    private double neicun;
    double yiyongneicun;
    double shengyvneicun;
    public String getName() {
        return name;
    }


    public void setName(String name) {
        this.name = name;
    }


    public double getNeicun() {
        return neicun;
    }


    public void setNeicun(double neicun) {
        this.neicun = neicun;
    }
    
    
    public double getYiyongneicun() {
        return yiyongneicun;
    }


    public void setYiyongneicun(double yiyongneicun)
    {
            this.yiyongneicun = yiyongneicun;
    }
    public void shengyvneicun()
    {
        neicun-=yiyongneicun;//==>neicun=neicun-yiyongneicun
        shengyvneicun=neicun;
//        if(shengyvneicun<0)
//        {
//            System.out.println("您的内存不足");
//        }
//        else if(shengyvneicun==neicun)
//        {
//            System.out.println("您的内存已用完");
//        }
//        else
//        {
        System.out.println("剩余内存："+shengyvneicun+"G.");
//        }
    }

    public Phone(String name, double neicun) {
        super();
        this.name = name;
        this.neicun = neicun;
    }
    
    public static void main(String[] args) {
        // TODO 自动生成的方法存根
        
        Phone myphone=new Phone("三星",100);
        System.out.println("手机品牌是："+myphone.getName());
        System.out.println("内存是"+myphone.getNeicun()+"G的。");
        myphone.yiyongneicun=2;
        System.out.println("手机已用内存;"+myphone.yiyongneicun+"G.");
        myphone.shengyvneicun();
        //myphone.setYiyongneicun(1);
        
    }
}

手机品牌是：三星
内存是100.0G的。
手机已用内存;2.0G.
剩余内存：98.0G.

解除代码中注释部分，运行出错，跪求老师讲解。

错误输出结果：

手机品牌是：三星
内存是100.0G的。
手机已用内存;2.0G.
您的内存已用完