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我尝试在 BankAccounts 的数组列表上实现可比较的接口，但是，在尝试编译和运行测试器类的主要方法时，我遇到了重大错误，特别是关于 Collection.sort(list) 行。据说它无法识别语法..在网上和通过javadoc查看，我找不到我错的地方..

public class BankAccount implements Comparable { //QUESTION 2.1
  /**
  A bank account has a balance that can be changed by 
  deposits and withdrawals.
 */
  private int accountNumber;
   private double balance; 
  /**
  Constructs a bank account with a zero balance
  @param anAccountNumber the account number for this account
  */
  public BankAccount(int anAccountNumber)
  {   
  accountNumber = anAccountNumber;
  balance = 0;
  }

   /**
  Constructs a bank account with a given balance
  @param anAccountNumber the account number for this account
  @param initialBalance the initial balance

*/ public BankAccount(int anAccountNumber, double initialBalance) {
accountNumber = anAccountNumber; 余额=初始余额；}

  /**
  Gets the account number of this bank account.
  @return the account number
  */
  public int getAccountNumber()
  {   
   return accountNumber;
   } 

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

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

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


   public int compareTo (BankAccount temp) {


     if (balance<temp.balance) 
         return -1;
     if (balance==temp.balance) 
         return 0;
     return 1;
  }

}

 public class TestSortedBankAccounts {

    public static void main(String[] args) {
        // Put bank accounts into a list 
        ArrayList<BankAccount> list = new ArrayList<BankAccount>();

        BankAccount ba1 = new BankAccount(100, 500); //Constructor acctNumber and balance
        BankAccount ba2 = new BankAccount(200, 10000);
        BankAccount ba3 = new BankAccount(300, 400);
        BankAccount ba4 = new BankAccount(600, 0);
        BankAccount ba5 = new BankAccount(800, 50);

        list.add(ba1);
        list.add(ba2);
        list.add(ba3);
        list.add(ba4);
        list.add(ba5);

        // Call the library sort method
        Collections.sort(list);

        // Print out the sorted list 
        for (int i = 0; i < list.size(); i++) {
            BankAccount b = list.get(i);
            System.out.println(b.getBalance());
        }
    }
}

更新：TestSortedBankAccounts.java:26：错误：没有找到适合 sort(ArrayList) Collections.sort(list) 的方法；^ 方法 Collections.sort(List,Comparator) 不适用（无法从参数实例化，因为实际参数列表和形式参数列表的长度不同）方法 Collections.sort(List) 不适用（推断类型不符合声明的边界）推断：BankAccount bound(s): Comparable) 其中 T#1,T#2 是类型变量：T#1 扩展方法 sort(List,Comparator) 中声明的对象 T#2 扩展方法 sort(List) 中声明的 Comparable 1错误

4

2 回答 2

4

您正在实施Comparable. 您应该实现以下通用形式Comparable：

public class BankAccount implements Comparable<BankAccount> {

如果您实现原始表单，则参数类型compareTo为Object. 使用泛型形式，您可以提供泛型类型参数compareTo作为您已有的参数。

于 2013-10-29T00:15:01.393 回答
0

我的答案（我已经尝试过并且有效）：

public class BankAccount implements Comparable<Object> { // <-- 
  /**
  A bank account has a balance that can be changed by 
  deposits and withdrawals.
 */
  private int accountNumber;
   private double balance; 
  /**
  Constructs a bank account with a zero balance
  @param anAccountNumber the account number for this account
  */
  public BankAccount(int anAccountNumber)
  {   
  accountNumber = anAccountNumber;
  balance = 0;
  }

   /**
  Constructs a bank account with a given balance
  @param anAccountNumber the account number for this account
  @param initialBalance the initial balance
  */ 
  public BankAccount(int anAccountNumber, double initialBalance) {
      accountNumber = anAccountNumber; balance = initialBalance; }

  /**
  Gets the account number of this bank account.
  @return the account number
  */
  public int getAccountNumber()
  {   
   return accountNumber;
   } 

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

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

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


   // public int compareTo (BankAccount temp) { // <-- WRONG
   public int compareTo(Object temp){ // <-- RIGHT

     BankAccount other = (BankAccount)temp; // <-- Cast to BankAccount
     if (balance<other.balance) 
         return -1;
     if (balance==other.balance) 
         return 0;
     return 1;
  }

}
于 2014-09-23T17:01:54.710 回答