CODEWITHSUNDEEP
javaarraylist
Aesculus
Aesculus

Reputation: 1

adding numbers to a array list and then adding up the numbers

I'm confused on how I would add the random numbers generated to the array list and then add them up at the end.

ArrayList<Coin> change = new ArrayList<Coin>();

// Generate a random number for how many coins 1-10
ArrayList<Integer> a = new ArrayList<Integer>();
int rand = (int) Math.round(Math.random() * 10 + 1);
a.add(rand);
for(int i=0;i< 0;i++) 
    System.out.println( (int)(Math.random()*10 + 1) + " Coins");


 // Generate a random number 1,2,3,4 to represent which coin
 System.out.println( (int)(Math.random()*4 + 1));

 // Create a new Coin of that type and add it to the list
 change.add(new Quarter());
 System.out.println(change);

 // Evaluate the full worth of the coins in the list

Upvotes: 0

Views: 114

Answers (2)

Basil Bourque
Basil Bourque

Reputation: 338326

The Answer by vsfDawg may be more useful.

Just for fun, here is an alternative code example using type-safe objects defined in an enum, generated and totaled via streams. This code is not an good starting place for a beginning student of Java. But this code can make an interesting contrast. And you could deconstruct the logic of this code to write more conventional Java code as a way to do your schoolwork assignment.

Note that as of Java 16+, enums (and records, and interfaces) can be declared locally.

enum Coin
{
    PENNY( 1 ), NICKEL( 5 ), DIME( 10 ), QUARTER( 25 ), HALF_DOLLAR( 50 ), DOLLAR( 100 );

    // Member fields.
    private int cents;

    // Constructors.
    Coin ( int cents ) { this.cents = cents; }

    // Getters.
    public int getCents ( ) { return cents; }
}

Generate a series of random index numbers (annoying zero-based counting) to access the array of named objects defined in the array.

int size = 10, lowBound = 0, highBound = 6 ;
List < Coin > coins =
        ThreadLocalRandom
                .current()
                .ints( size , lowBound , highBound )
                .mapToObj( i -> Coin.values()[ i ] )
                .toList();

Calculate the total value of the coins.

int total =
        coins
                .stream()
                .mapToInt( coin -> coin.getCents() )
                .sum();

Dump to console.

System.out.println( "coins = " + coins );
System.out.println( "total = " + total );

When run.

coins = [PENNY, DIME, NICKEL, NICKEL, NICKEL, NICKEL, PENNY, DIME, NICKEL, PENNY]

total = 48

Upvotes: 0

vsfDawg
vsfDawg

Reputation: 1527

You are already populating the List a with random numbers so I'll focus on the ' add them up at the end' part.

Any time you are performing some sort of operation it is a good idea to encapsulate that operation in a separate method. This helps to clarify where responsibilities begin and end. In this case, define a method to calculate the sum of the values in the List. Here's one using a for-each loop.

public int sumValues(List<Integer> list) {
  int sum = 0;
  for (Integer value : list) {
    sum += value;
  }
  return sum;
}

Using the Stream API can simplify this further.

public int sumValues(List<Integer> list) {
  return list.stream().reduce(0, Integer::sum);
}

Upvotes: 1

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