Public class implements Comparable

Question

I have an Public class Account that i want to implement with comparable and my question is the following:

how can I make that the account with the lowest balance is the "smallest" in my comparison?.

public class Account implements Comparable<Account>{
  private double balance;
  private String acctNum;

  public Account(String number, double initBal){
      balance = initBal;
      acctNum = number;
  }
  public double getBalance(){
      return balance;
  }
  .....


 public int compareTo(Account other) {
         ????????
  }

Did you read [the docs](https://docs.oracle.com/javase/7/docs/api/java/lang/Comparable.html#compareTo%28T%29) for that method? — resueman, Apr 11 '16 at 20:33
[This method](https://docs.oracle.com/javase/7/docs/api/java/lang/Double.html#compare(double,%20double)) might be helpful to you. — Andy Turner, Apr 11 '16 at 20:35

ericbn · Answer 1 · 2016-04-11T20:43:35.353

The compareTo method must return:

a negative integer if this is less than other,
zero if this is equal to other
a positive integer if this or greater than other

Just doing return this.balance - other.balance can give invalid results if values are near Double.MAX_VALUE or Double.MIN_VALUE, so you should use Double.compare:

public int compareTo(Account other) {
    return Double.compare(this.balance, other.balance);
}

score 0 · Answer 2 · answered Apr 11 '16 at 20:38

0

The simplest way to implement is to use a Double as the type for balance and simply call compareTo method:

return balance.compareTo(other);

I'm not saying that this is the best but it is good enough for a start.

Note that handling nulls is up to you to implement.

answered Apr 11 '16 at 20:38

Adam Arold

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This wouldn't compile. That's not how autoboxing works. – Andy Turner Apr 11 '16 at 20:44
@AndyTurner It says use `Double`. It wouldn't compile because `other` is not a `Double`. – Paul Boddington Apr 11 '16 at 20:48
@PaulBoddington it wouldn't compile because `balance` is a `double`, not a `Double`, and you can't invoke `compareTo` on a `double`. – Andy Turner Apr 11 '16 at 20:53
@AndyTurner Read the full answer again... It's a strange answer, but that is not the problem. – Paul Boddington Apr 11 '16 at 20:54
@PaulBoddington [you can't invoke `compareTo` on a `double`](http://ideone.com/HUyBK9). – Andy Turner Apr 11 '16 at 20:55
That's why I said he should use `Double`. The other answer is just as good or even better. – Adam Arold Apr 11 '16 at 20:55
@AndyTurner which part of "The simplest way to implement is to use a `Double` as the type for balance " you don't understand? – Adam Arold Apr 11 '16 at 20:56
The bit where I misread it and you didn't simply use `Double.compareTo` :) – Andy Turner Apr 11 '16 at 20:56

Public class implements Comparable

2 Answers2