对具有共同实例变量的各种对象的 ArrayList 进行排序

Question

我最近一直在研究接口，并且能够成功实现 Comparable 并按数量对 ArrayList 个 BankAccount 个对象进行排序。

但是，如果 ArrayList 包含 BankAccount 和 Country 类型的对象，并且具有实例变量 "area"（双精度）。它们都具有 double 类型的值，可以进行比较和排序。

所以我的第一个问题是—— 如何对包含具有 double 作为实例变量的各种对象的 ArrayList 进行排序？

这是我的代码：

/**
   A bank account has a balance that can be changed by 
   deposits and withdrawals.
*/
public class BankAccount implements Measurable, Comparable<BankAccount>
{  
  private Double balance;

   /**
      Constructs a bank account with a zero balance.
   */
   public BankAccount()
   {   
      balance = 0.0;
   }

   /**
      Constructs a bank account with a given balance.
      @param initialBalance the initial balance
   */
   public BankAccount(Double initialBalance)
   {   
      balance = initialBalance;
   }

   /**
      Deposits money into the bank account.
      @param amount the amount to deposit
   */
   public void deposit(Double amount)
   {  
      balance = balance + amount;
   }

   /**
      Withdraws money from the bank account.
      @param amount the amount to withdraw
   */
   public void withdraw(Double amount)
   {   
      balance = balance - amount;
   }

   /**
      Gets the current balance of the bank account.
      @return the current balance
   */
   public double getBalance()
   {   
      return balance;
   }

   public double getMeasure()
   {
      return balance;
   }
     public int compareTo(BankAccount o)
  {
    return this.balance.compareTo(o.getBalance());


  }
}

/**
   A country with a name and area.
*/
public class Country implements Measurable
{
   private String name;
   private double area;

   /**
      Constructs a country.
      @param aName the name of the country
      @param anArea the area of the country
   */
   public Country(String aName, double anArea) 
   { 
      name = aName;
      area = anArea; 
   }

   /**
      Gets the country name.
      @return the name
   */
   public String getName() 
   {
      return name;
   }

   /**
      Gets the area of the country.
      @return the area
   */
   public double getArea() 
   {
      return area;
   }

   public double getMeasure() 
   {
      return area;


      }
    }


    public interface Measurable
    {
       double getMeasure();  // An abstract method
    }

import java.util.*;
public class MeasurableTester 
{
   public static void main(String[] args)
   {
      // Calling the average method with an array of BankAccount objects
    BankAccount b=new BankAccount(10.0);
    BankAccount c = new BankAccount(2000.0);
     List<BankAccount> accounts = new ArrayList<BankAccount>();

      accounts.add(b);
      accounts.add(c);


     BankAccount x= Collections.max(accounts);
      System.out.println(x.getBalance());
   }


}

Answer 1

您应该使用可测量列表并使用比较器：

  List<Measurable> measurableList = new ArrayList<>();
  measurableList.add(new BankAccount(10.0));
  measurableList.add(new Country("name", 44.5));

  measurableList = Collections.max(measurableList, Comparator.comparingDouble(Measurable::getMeasure));

对具有共同实例变量的各种对象的 ArrayList 进行排序

Sorting an ArrayList of various objects having in common instace variable being a double

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comparable