Java - 使用 ArrayList/HashSet 查询的搜索结果进行菜单选择

Question

I'm wondering if anyone can give me some pointers on what the next steps in a basic program I have.

I have the following example java code:

import java.util.ArrayList;
import java.util.Scanner;

public class Main {

    ArrayList<Transport> transportList = new ArrayList<>();
    Scanner input = new Scanner(System.in);

    public void addToList() {
        transportList.add(new Transport("Blue", "Large", "Plane"));
        transportList.add(new Transport("Red", "Small", "Car"));
        transportList.add(new Transport("Brown", "Large", "Train"));
        transportList.add(new Transport("Yellow", "Small", "Boat"));
        transportList.add(new Transport("Yellow", "Small", "Plane"));
        transportList.add(new Transport("Brown", "Large", "Car"));
        transportList.add(new Transport("Red", "Large", "Train"));
        transportList.add(new Transport("Blue", "Small", "Boat"));

        searchColour();
    }

    public void searchColour() {
        System.out.println("Enter a colour to search:\n");
        String colourSearch = input.next();
        for (Transport transport : transportList) {
            if (transport.getColour().toLowerCase().equals(colourSearch.toLowerCase())) {
                System.out.printf(
                    "There is a %s %s that is %s \n",
                    transport.getSize(),
                    transport.getType(),
                    transport.getColour()
                );
            }
        }
        searchColour();
    }

    public static void main(String[] args) {
        new Main().addToList();
    }
}

public class Transport {

    private String colour;
    private String size;
    private String type;

    // All-args constructor, getters and setters omitted for brevity
}

This runs and prompts the user to enter a colour. It then searches the ArrayList and outputs the matches. What I now need to do is to take the results I get from a colour search and reuse them in a menu for selection.

For example if I search for "red", I get:

There is a Small Car that is Red

There is a Large Train that is Red

What I want is to have a number placed in front of them and another prompt to choose which one the person whats. So it should say something like:

1. There is a Small Car that is Red
2. There is a Large Train that is Red

"Choose which transport you want"

Outputting the next question and prompting for an input with Scanner I can do, I'm not sure how I can add numbers to the start of the results, knowing that as my ArrayList grows the number of items will, and how I do a selection choice from it so a user can press 1 or 2.

Can anyone offer a suggestion? I'm thinking I need to use another ArrayList but I'm not sure how this should be structured.

Answer 1

I think you should make use of the fact, that an ArrayList keeps the elements in insertion order. You could eg use the "indexOf(Object o)" method to get the number you want to be printed. (You have to add 1 to get your example, because it starts with 0.)

And to select the item you can use "get(int index)" and let the user type the index. (here you have to substract 1, like above.)

Answer 2

What you want is a counter. Create an int variable to keep track of the question number.

When the user inputs a number, use the List's get method to retrieve the choice:

public void searchColour() {
    System.out.println("Enter a colour to search:\n");
    String colourSearch = input.next();

    int questionNumber = 1;
    for (Transport transport : transportList) {
        if (transport.getColour().toLowerCase().equals(colourSearch.toLowerCase())) {
            System.out.printf(
                "%d. There is a %s %s that is %s \n",
                questionNumber++,
                transport.getSize(),
                transport.getType(),
                transport.getColour()
            );
        }
    }

    int choice;
    do {
        System.out.println();
        System.out.println("Choose which transport you want:");
        choice = input.nextInt();
    } while (choice < 1 || choice > transportList.size());

    // List indices start at zero, not one.
    Transport transport = transportList.get(choice - 1);

    System.out.printf("You chose a %s %s that is %s%n",
                transport.getSize(),
                transport.getType(),
                transport.getColour()
}

The println method prints a newline after printing the argument you pass it. Therefore, you don't need to pass a String ending with \n , unless you really want to print a blank line after the text (and that may not work in Windows, where a newline sequence is actually the two characters \r\n ).

In the printf method, you can use the special Formatter sequence %n instead of a literal \n to make sure the system's newline sequence is always used.