Question

我在使用该类对象的arraylist从类中获取历史记录时遇到问题，因为每次调用方法时arraylist都会重新初始化这是我的代码：

public class User_Interface2 {
    ArrayList<Removable> re=new ArrayList<Removable>();
    private final ArrayList<Internal> in=new ArrayList<Internal>();
    ArrayList<External> ex=new ArrayList<External>();

public static void main(){
User_Interface2 q=new User_Interface2();
    System.out.println("Choose from the below options");
    System.out.println("1.Internal Storage");
    System.out.println("2.Removable device");
    System.out.println("3.External Drive");
     Scanner sc=new Scanner(System.in);
    int a=sc.nextInt();
    sc.nextLine();
    System.out.println("Enter the name of the file");

    String s=sc.nextLine();
    System.out.println("Enter the size of the file in GB");
    double d=sc.nextDouble();

    q.saveData(a,s,d);


}
public void saveData(int a,String s,double d){

    switch (a) {
        case 1:

            in.add(new Internal());
            in.get(in.size()-1).nameoffile=s;
            in.get(in.size()-1).size=d;

            in.get(in.size()-1).capacity();

            break;
        case 2:
            re.add(new Removable());

            re.get(re.size()-1).nameoffile=s;
            re.get(re.size()-1).size=d;

            re.get(re.size()-1).capacity();

            break;
        case 3:
            ex.add(new External());

            ex.get(ex.size()-1).nameoffile=s;
            ex.get(ex.size()-1).size=d;

            ex.get(ex.size()-1).capacity();

            break;
        default:
            System.out.println("No such storage option available");
            break;
    }

}

}

这是内部类：

public class Internal extends Storage {
static double capacity=1024;
String nameoffile;
public double size;
void capacity(){
    capacity=capacity-size;
    System.out.println("Remaining capacity: "+capacity+"GB");
}
void persistent_save(){}

}

每当从另一个类调用User_Interface2类的main方法并且数据存储在内部类中时，在退出此类之后，arraylist将自行清除，并且我无法看到存储数据的历史记录。

这是我调用User_Interface2类的方法：

void Laptop(){
    User_Interface2 d;
    System.out.println("Welcome to Your Laptop");
    System.out.println("Choose from the below options");
    System.out.println("1.Show details of the laptop");
    System.out.println("2.Display the data stored in your laptop");
    System.out.println("3.Save Data");

    System.out.println("4.Charge your Laptop");
    System.out.println("0 to exit");
    Scanner sc=new Scanner(System.in);
    int a=sc.nextInt();
    sc.nextLine();
    while(a!=0){
    if(a==1)
    {processor();
    Ram();
    MotherBoard();}
    else if(a==2)
    {d=new User_Interface2();
    d.showData();}
    else if(a==3)
    {d=new User_Interface2();
    d.main();}

    else if(a==4)
    {charge();}
   else
    {System.out.println("No such Option is available");}
   System.out.println("Welcome to Your Laptop");
    System.out.println("Choose from the below options");
    System.out.println("1.Show details of the laptop");
    System.out.println("2.Display the data stored in your laptop");
    System.out.println("3.Save Data");

    System.out.println("4.Charge your Laptop");
    System.out.println("0 to exit");
    //Scanner sc=new Scanner(System.in);
    a=sc.nextInt();
    sc.nextLine();
}
}

}

Answer 1

快速回顾一下这个街区：

while(a!=0){
... 
else if(a==2)
{d=new User_Interface2();
d.showData();}
else if(a==3)
{d=new User_Interface2();
d.main();}
}

您正在每次迭代时创建一个新实例。在循环外创建d并重用该实例。

d=new User_Interface2();
while(a!=0){
    ...
    else if(a==2) {
        d.showData();
    } else if(a==3) {
        d.main();
    }
}

调用方法时，ArrayList正在重新初始化

1 个答案: