CODEWITHSUNDEEP
javaif-statement
WillumMaguire
WillumMaguire

Reputation: 547

How to avoid an else if marathon in Java?

I am beginning Java programming, and I have written a program which tests how many moons each planet has. Here is a shortened version with only four of the planets.

import java.util.Scanner;
import java.util.Random;

public class one {
    public static void main(String args[]){
        //SET VARIABLES
        String zero="Mercury", one="Venus", two="Earth", three="Mars";
        //SET VARIABLES
        for (int x=1; x<=1000; x++){
            System.out.println("Moons");
            Random r = new Random();
            for (int y=1; y<=1; y++){
                int rI = r.nextInt(4);
                if (rI == 0){
                question(zero,0);
                }
                else if (rI == 1){
                question(one, 0);
                }
                else if (rI == 2){
                question(two, 1);
                }
                else if (rI == 3){
                question(three, 2);
                }
            }
        }
    }

    public static void question(String n, int num){
    Scanner input = new Scanner(System.in);
    System.out.print("How many moons does " + n + " have? ");
    int ans = input.nextInt();
    if (ans == num){
        System.out.println("Correct!");
    }
    else if (ans != num){
        System.out.println("Incorrect!");
        question(n, num);
    }
    }
}

How would I go about not having to write "else if" so many times? This becomes very tedious with more statements. Keep in mind I am a beginner, and this code is about the limit of my current abilities.

Upvotes: 2

Views: 366

Answers (8)

Akos K
Akos K

Reputation: 7133

I would start with forgetting that vector-thing and putting Planets and their Moons together in a POJO (Plain Old Java Object) and putting those objects into the Array:

class Planet {

    int moons;
    String name;

    Planet(String name, int moons) {
         this.name = name;
         this.moons = moons;
    }

    public String getName() {
        return this.name;
    }

    public getMoons() {
        return this.moons;
    }

    public void question(){
        Scanner input = new Scanner(System.in);
        System.out.print("How many moons does " + this.name + " have? ");
        int ans = input.nextInt();
        if (ans == this.moons){
            System.out.println("Correct!");
        }
        else {
            System.out.println("Incorrect!");
        }
    }
}

public class one {
    public static void main(String args[]){
        //SET VARIABLES
        List<Planet> planets = new ArrayList<Planets>();
        Planet earth = new Planet("Earth", 1);
        // put other planets
        //SET VARIABLES
        for (int x=1; x<=1000; x++) {
            System.out.println("Moons");
            Random r = new Random();
            int rI = r.nextInt(planets.size());
            Planet p = planets.get(rI);
            p.question();
        }
    }
}

Upvotes: 0

martijno
martijno

Reputation: 1783

I would prefer enums over arrays here. See this enums tutorial (especially the planets example ;) ). Add another field (just like mass and radius) for moon count.

Upvotes: 0

Reimeus
Reimeus

Reputation: 159874

You could use arrays like so:

String[] planets = { "Mercury", "Venus", "Earth", "Mars" };
int moons[] = { 0, 0, 1, 2 };

and call:

if (rI >= 0 && rI < planets.length) {
    question(planets[rI], moons[rI]);
}

Upvotes: 4

arshajii
arshajii

Reputation: 129572

You could use the switch keyword:

switch (rI) {
    case 0:
        question(zero, 0);
        break;
    case 1:
        question(one, 0);
        break;
    case 2:
        question(two, 1);
        break;
    case 3:
        question(three, 2);
        break;
    default:
        // do something
}

The code under default executes when no match is found.

You could also use arrays:

String[] planets = new String[]{"Mercury", "Venus", "Earth", "Mars"};
int[] nums = new int[]{0, 0, 1, 2};
...
// in the loop:
question(planets[rI], nums[rI]);

Of course, there are other ways to approach the problem, but I think for someone who is just learning these should do the trick. One thing you might want to look into, however, (once you get deeper into Java), is the concept of a Map, much like a dictionary in Python. You could maintain a map that maps a planet (string) to the number of moons it has (int).

Upvotes: 0

Philipp
Philipp

Reputation: 4749

You could go with switch or if-else as long as you logic does not evolve. Otherwise you need to start the object-oriented programming. Create a class "Planet" and another class for each planet that inherits from Planet and add the planet specific information to each of it. Then you're good for the future when you may plan to add some more questions for the planets.

Upvotes: 1

fatrock92
fatrock92

Reputation: 837

A better way to write this code. It is more readable and it is very easy to make any updates.

import java.util.Scanner;
import java.util.Random;

public class one {
    public static void main(String args[]){
        //SET VARIABLES
        String planets []=new String[4];
        planets[0]="Mercury";
        planets[1]="Venus";
        planets[2]="Earth";
        planets[3]="Mars";
        int moons []=new int[4];
        moons[0]=0;
        moons[1]=0;
        moons[2]=1;
        moons[3]=2;
        //SET VARIABLES
        while(true){
            System.out.println("Moons");
            Random r = new Random();
            int rI = r.nextInt(4);
            question(planets[rI],moons[rI]);
        }
    }

    public static void question(String n, int num){
        Scanner input = new Scanner(System.in);
        System.out.print("How many moons does " + n + " have? ");
        int ans = input.nextInt();
        if (ans == num){
            System.out.println("Correct!");
        }
        else if (ans != num){
            System.out.println("Incorrect!");
            question(n, num);
        }
    }
}

Upvotes: 1

heretolearn
heretolearn

Reputation: 6555

You can try using switch instead of the long if-else ladder.

For more information on switch read the java documentation

In your case it could be something like:

switch (rI) {
    case 0:
        question(zero, 0);
        break;
    case 1:
        question(one, 0);
        break;
    case 2:
        question(two, 1);
        break;
    case 3:
        question(three, 2);
        break;
    default:
        break;
}

Upvotes: 0

David W
David W

Reputation: 10184

Take a look at the switch statement in Java. That is designed to help overcome a screwy if-elseif-elseif-elseif-else block:

switch(rI){
    case 2: question(two, 1);
            break;
    case 3: question(three, 2);
            break;
    default: doSomethingClever(...);
}

There are some other cleanups you could employ, but getting that switch block in place addresses your initial comment. Good luck.

Upvotes: 0

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