Having trouble adding elements to ArrayList in correct order

Question

So my program is supposed to iterate over a list of numbers (0-113) and then print the numbers line by line. If the number is odd, that should be added next to the number, if the number is divisible by 5, that should be added next to the number and so on. So I have my 4 boolean methods done and they look like this:

public static boolean isDivisibleBy5(int n){        
    if (n%5 ==0){           
        return true;
    }       
    return false ;          
}

Next I have a method that I am required to use as per assignment requirements and it is as follows:

public static ArrayList<String>iterate()

So the definition with this method is where I am having problems. Right now what I have is this:

public static ArrayList<String>iterate(){
    ArrayList<String> list = new ArrayList<String>();
    for(int i=0;i<114;i++){

    if (isOdd(i)){
    list.add(i+" Is odd");
    }
    if(isDivisibleBy5(i)){
        list.add(i+" hi five");
    }
    if(isDivisbleBy7(i)){
        list.add(i+" wow");
    }
    if (isPrime(i)){
        list.add(i+" prime");
    }
    }
    for(String elem:list)
    System.out.println(elem);
    return list;

}

But unfortunately my output looks like this:

0 hi five
1 Is odd
1 prime
3 Is odd
3 wow
3 prime
5 Is odd
5 hi five
5 prime
7 Is odd
7 prime
9 Is odd
10 hi five
10 wow
11 Is odd

I need it to look like this:

0, hi five
1, Is Odd, prime
2
3, Is odd, wow, prime
4
5, Is Odd, hi five, prime

etc.

So my question is basically how do I get all the conditions (when true) to add themselves to the same line with the corresponding number and also have the numbers that don't meet the conditions print on their lines as well, like 2 and 4 and 6. I've been stuck on this question for awhile and I feel like there is a crucial piece of java that I am not thinking of that is required here. String Builder maybe? I'm not sure. Any help is appreciated. Even if you can just point me to a concept to look up and learn more of.

Thanks

EDIT: I am seeing a lot of responses about building the string first and then adding to it. I believe this was the concept that I was not thinking of that has held me back so I will read up and practice implementing that. Thanks again for the quick responses. When I get it working I will come back here and up-vote anyone who helped.

How about first constructing the whole String and THEN adding it to the list? — Turing85
– Turing85, Commented May 31, 2016 at 19:22
you can concat a String and add to array then. String conditions = ""; if (isOdd()) conditions += ", is odd": if (isPrime) conditions += ", is prime": list.add(i + "conditions); — Johnny Willer
– Johnny Willer, Commented May 31, 2016 at 19:22
Consider what you're storing. Right now, you're storing individual statements. You want to store grouped statements. So constructing a String, or an array or arraylist for each number would be beneficial, and then storing that construct in the original arraylist. — Compass
– Compass, Commented May 31, 2016 at 19:23

Jorn Vernee · Accepted Answer · 2016-05-31 19:24:30Z

2

You need to compose the string first and then add it only once:

public static ArrayList<String>iterate(){
    ArrayList<String> list = new ArrayList<String>();
    for(int i=0;i<114;i++){
        String toAdd = String.valueOf(i);    

        if (isOdd(i)){
            toAdd += ", Is odd";
        }
        if(isDivisibleBy5(i)){
            toAdd += ", hi five";
        }
        if(isDivisbleBy7(i)){
            toAdd += ", wow";
        }
        if (isPrime(i)){
            toAdd += ", prime";
        }

        list.add(toAdd);
    }

    for(String elem:list)
        System.out.println(elem);

    return list;    
}

answered May 31, 2016 at 19:24

Jorn Vernee

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1 Comment

user3516525 Over a year ago

Thanks for this. String.valueOf(i); is something I did not know of and everything I was trying to do relating to this wasn't working.

Alek Mieczkowski · Accepted Answer · 2016-05-31 19:24:13Z

0

So from what I see you're using list.add() and its adding a row every time you call it. Instead of using list.add() in every if statement, why don't you just add everything to a sting and then use list.add(string) to add it to your list?

Something like this:

public static ArrayList<String>iterate(){
    String line =""; //creates line
    ArrayList<String> list = new ArrayList<String>();
    for(int i=0;i<114;i++){
    line += i;
    if (isOdd(i)){
    line +=", Is odd";
    }
    if(isDivisibleBy5(i)){
     line += ", high five"
    }
    ...
    list.add(line);

answered May 31, 2016 at 19:24

Alek Mieczkowski

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