Type errors when sorting my array of objects

Question

I need to sort my array of Money objects in ascending order, but I get 3 compiler errors.

TestMoney.java:44: error: bad operand types for binary operator '<'
            if (list[j] < list[min]) {
                        ^
  first type:  Money
  second type: Money
TestMoney.java:50: error: incompatible types: Money cannot be converted to int
            final int temp = list[i];
                                 ^
TestMoney.java:52: error: incompatible types: int cannot be converted to Money
            list[min] = temp;
                        ^

class TestMoney
{
   public static void main(String [] args)
   {
      Money[] list = new Money[15];
      for(int i =0; i<15; i++)
      {
         int dollar =(int) (Math.random() * 30 + 1);
         int cent = (int) (Math.random() * 100);
         list[i] = new Money(dollar, cent);

      }
      sortArray(list);
      printArray(list);

   }
   public static void printArray(Money[] list)
   {
      for(int i =0; i <list.length; i++)
      {

         if(i%10 ==0)
         {
          System.out.println();
         }

         System.out.print(" " + list[i]);
     }

   }
   public static void sortArray(Money[] list)
   {
   int min;
    for (int i = 0; i < list.length; i++) {
        // Assume first element is min
        min = i;
        for (int j = i + 1; j < list.length; j++) {
            if (list[j] < list[min]) {
                min = j;

            }
        }
        if (min != i) {
            final int temp = list[i];
            list[i] = list[min];
            list[min] = temp;
        }
        System.out.println(list[i]);// I print the in ascending order
    }

  }
}

class Money
{
   private int dol;
   private int cen;

   Money()
   {
      dol = 0;
      cen = 00;
   }
   Money(int dol,int cen)
   {
      int remainder = cen % 100;
      int divisor = cen / 100;
      this.dol = dol+ divisor;
      this.cen = remainder;
   }
   public int getDollors(int dol)
   {
      return dol;
   }
   public int getCents(int cen)
   {
      return cen;
   }
   public void setDollors(int d)
   {
      dol = d;
   }
   public void setCents(int c)
   {
      cen = c;
   }
   public Money addMoney(Money m)
   {
      int d = this.dol + m.dol;
      int c = this.cen + m.cen;
      return new Money(d, c);
   }
   public int compareTo(Money m)
   {

     if(this.dol<m.dol && this.cen<m.cen)
     return -1;
     else if(m.dol<this.dol && m.cen<this.cen )
     return 1;
     return 0;


   }
   public Money subtract(Money m)
   {
      int cents1 = this.dol*100 + this.cen;
      int cents2 = m.dol *100 + m.cen;
      int cents = cents1 -cents2;
      return new Money(cen/100,cen%100);
   }


   public String toString()
   {

      return String.format("$%d.%02d", this.dol,this.cen);

   }
}

you need to implement the comparator class in order for the < to evaluate the two Money objects, check out this example - tutorialspoint.com/java/java_using_comparator.htm — RAZ_Muh_Taz
– RAZ_Muh_Taz, Commented Apr 4, 2017 at 22:46
Read the code you posted. int temp = list[i], when list[i] is Money, clearly isn't going to work. int is not the same as Money, so they're not assignment compatible. Did you even read the error message? — Ken White
– Ken White, Commented Apr 4, 2017 at 22:48
You can't convert between an object (Money) and a value (int). What would you expect that to do? — David
– David, Commented Apr 4, 2017 at 22:49
Your getters aren't doing what you think they're doing. They just return the value you pass them, they don't return anything from the object. — David
– David, Commented Apr 4, 2017 at 22:50

Darshan Mehta · Accepted Answer · 2017-04-07 21:18:59Z

1

That's because you are trying to compare two Money objects with < operator which applies to Numbers only, you need to replce the following:

if (list[j] < list[min]) {

with

if (list[j].getDollors() < list[min].getDollors() 
    || (list[j].getDollors() == list[min].getDollors() && list[j].getCents() < list[min].getCents())) {

Also, you don't need your getters to accept an argument, they can be zero argument methods as they just return a value.

edited Apr 7, 2017 at 21:18

answered Apr 4, 2017 at 22:49

Darshan Mehta

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1 Comment

CrazyGal Over a year ago

Thank you so much !

developer_hatch · Accepted Answer · 2017-04-07 18:40:16Z

0

Another way, maybe, is using Comparator interface, like this:

public class Money implements Comparator<Money>{
int n; //as an example, compare two object by them "n" variable

@Override
public int compare(Money o1, Money o2) {
    int result;
    if (o1.n > o2.n)
        result = 1; //greater than case
    else
        result = o1.n < o2.n ? -1 // less than case
                : 0; // equal case
    return result;
}

}

In the compare method you can use the criteria of gt-ls-eq based on amount of money. Finally do:

for (int j = i + 1; j < list.length; j++) {
        if (list[j].compare(list[min]) < 0) { //you ask if is greater, less,
                                              //or equal than 0
            min = j;
        }
}

edited Apr 7, 2017 at 18:40

answered Apr 5, 2017 at 20:01

developer_hatch

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3 Comments

CrazyGal Over a year ago

Thanks alot ! I appreciate this

CrazyGal Over a year ago

I put you a thumbs up..but it won't show for you because I'm new here

developer_hatch Over a year ago

It's ok! I'm glad I could help you

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