如何在Java中使用ArrayList添加元素？

Question

I'm now learning all about ArrayList . I've created a small code for practice purposes using ArrayList but there has been an unwanted output.

My output should be like this:

********************\\

1 - Add names

2 - Show names

Enter mode:1

Enter name:Bruno

Do you want to add a name again?(y/n):y

Enter name:Django

Do you want to add a name again?(y/n):n

********************\\

1 - Add names

2 - Show names

Enter mode:2

Bruno

Django

but instead, my output is like this:

********************\\

1 - Add names

2 - Show names

Enter mode:1

Enter name:Bruno

Do you want to add a name again?(y/n):y

Enter name:Django

Do you want to add a name again?(y/n):n

********************\\

1 - Add names

2 - Show names

Enter mode:2

When I have already added the names and then press n , I will choose next, the number 2 for displaying names. But it didn't show anything. I can't figure out the algorithm. It looks like the ArrayList is resetting its elements whenever it went back to choosing mode.

Here is my code:

package Practice;
import java.util.Scanner;
import java.util.ArrayList;
public class Practice1Main {

    public static void main(String[]args){
    ArrayList<String>namelist=new ArrayList<>();

    Scanner hold = new Scanner(System.in);
    String response, name;
    int mode = getMode();

    switch(mode){
    case 1:

        do{
            System.out.print("Enter name:");
            name = hold.nextLine();
            namelist.add(name);

            System.out.print("Do you want to add a name again?(y/n):");
            response = hold.nextLine();
            if(response.equalsIgnoreCase("n")){
                getMode();
            }

        }while(response.equalsIgnoreCase("y"));
        break;
    case 2:
        for(int x = 0;x < namelist.size();x++){
            System.out.println(namelist.get(x));
        }
        break;
    default:
        System.out.print("ERROR!");
        break;
    }

}



public static int getMode(){
    Scanner hold = new Scanner(System.in);

    int mode;
    System.out.print("********************\n");
    System.out.print("1 - Add names\n");
    System.out.print("2 - Show names\n");
    System.out.print("Enter mode:");
    mode = hold.nextInt();

    return mode;
}

}

Answer 1

Well, a quick solution is below...

You miss setting mode when reading the getMode again, and also you do nothing when looping next time (the switch must activate again, you know.. I set it in a while loop). study below

    while( mode == 1 || mode == 2 ) {
    switch(mode){
    case 1:
        do{
            System.out.print("Enter name:");
            name = hold.nextLine();
            namelist.add(name);

            System.out.print("Do you want to add a name again?(y/n):");
            response = hold.nextLine();
            if(response.equalsIgnoreCase("n")){
                mode = getMode(); // <---- set mode
            }

        }while(response.equalsIgnoreCase("y"));
        break;
    case 2:
        for(int x = 0;x < namelist.size();x++){
            System.out.println(namelist.get(x));

        }
        mode=-1; // <--- break out
        break;
    default:
        System.out.print("ERROR!");
        mode = -1; 
        break;
    }
}
}