Java How to use an array in a switch method

Question

I'm trying to learn Java and I'm working on my project "Collection of programs" // very simple ones: like a basic calculator, factorials, reversing numbers etc. These programs are divided into categories like Mathematics, Drawings ... The problem is that maybe in the future I will want to have more categories/programs in it. I want to use arrays so I don't have to re-write my code every time I add a new program/category.

I have created an array of strings and updated my method welcomeUser. But I don't know how to deal with my chooseBlock method and switch. I would like to have as many cases as blocks in my Array.

Thank you very much for every help

public class Program {

    Scanner scan = new Scanner(System.in);

    private boolean programRunning = true;

    public void run() {
        System.out.println("Welcome in my program! (version 1.0.0)");
        while (programRunning) {
            welcomeUser();
            chooseBlock();
        }

    }

    public void welcomeUser() {
        System.out.println("You can choose from these blocks:\n"
                + "[1.Mathematic Block]\t"
                + "[2.Drawing block]\t"
                + "[3.Else...]\t"
                + "[4.Exit]\n"
                + "Select with a number and press ENTER");
    }

    public void chooseBlock() {
        int block = 0;
        block = scan.nextInt();
        switch (block) {
            case 1:
                System.out.println("You've choosen Mathematic Block");
                Mathematics maths= new Mathematics();
                maths.run();
                break;
            case 2:
                System.out.println("You've choosen Drawing block");
                Drawings drawings = new Drawings();
                drawings.run();
                break;
            case 3:
                System.out.println("You've choosen Else block");
                break;
            case 4:
                System.out.println("Exiting the program");
                programRunning = false;
                break;
            default:
                System.out.println("Invalid input. Try again.");
                break;
        }
        System.out.println("");
    }

}

private String[] blocks
        = {"Mathematic Block", "Drawing Block", "Else", "Exit"};

public void welcomeUser() {

   System.out.println("You can choose from these blocks:\n");
   for (int i = 0; i < blocks.length; i++) {
        System.out.print("[" + (i + 1) + ". " + blocks[i] + " ]\t");
        if ((i + 1) % 4 == 0) {
            System.out.println();
        }
   }
   System.out.println();
   System.out.println("Select with a number and press ENTER");
}

Your problem is a design problem. I.e. how to make this app easy to extend. That's a difficult problem, usually not for beginners. Moreover, there is more than one good answer for this kind of problems. I suggest to keep your code as simple as possible. This makes things easy later on. No need to use Arrays when you don't need them right now. When you want to add another category, then you can ask a question about that. — Tamas Rev
– Tamas Rev, Commented Apr 12, 2018 at 11:17
The short answer, you want to use something like the strategy pattern. Each category will have it own strategy implementation. When you need to add a new category, you implement a new strategy. Know, instead of a switch you just have to get the instance of Strategy that is store in an array, the index will match the array of category. Simple and evolutive. But the first implementation take time since you need to have a strategy well defined. Strategy or State pattern are two similar, I might mix those... — AxelH
– AxelH, Commented Apr 12, 2018 at 11:23

lexicore · Accepted Answer · 2018-04-12 11:34:23Z

1

Basically you want easy extensibility of categories. There are many ways to achieve this. I'll sketch one approach for starters.

First of all I'd explicitly model categories in a class like Category:

public abstract class Category {
    public abstract String getTitle();
    public abstract void run();
}

Each of the specific categories will have its own class, extending Category

public class Mathematics extends Category {
    public String getTitle() { return "Mathematic Block";}
    public void run() { ... }
}

Then you'll have a list of availabe categories:

private List<Category> categories = Arrays.asList(new Mathematics(), ...);

Now you can display the list of available categories as follows:

public void welcomeUser() {
    System.out.println("You can choose from these blocks:");
    for (int index = 0; index < categories.size(); index++) { 
        Category category = categories.get(index);
        System.out.println("[" + (index+1) + "." + category.getTitle() + "]");
    }
    // ...
}

And instead of switch you can do:

int block = scan.nextInt();
int selectedCategoryIndex = block - 1;
if (selectedCategoryIndex >= 0 && selectedCategoryIndex < categories.size()) {
    Category selectedCategory = categories.get(selectedCategoryIndex);
    selectedCategory.run();
}

If there's a new category, just add it to categories.

answered Apr 12, 2018 at 11:34

lexicore

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2 Comments

user9635657 Over a year ago

Thank you all. I'm going to try it.

lexicore Over a year ago

@user9635657 If you feel that my answer helped you, you could accept my answer.

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