Java 类型不匹配 : cannot convert from java. lang.Object

Question

我正在使用 Blue Pelican Java 教科书并使用 drjava。我目前正在从事第 43 课 Big Bucks 项目，基本上我必须使用这个 BankAccount 类:

public class BankAccount
{
  public BankAccount(String nm, double amt)
  {
    name = nm;         
    balance = amt;        
  }     
  public void deposit(double dp)  
  {    
    balance = balance + dp;   
  }        
  public void withdraw(double wd)  
  {        
    balance = balance - wd;   
  }    
  public String name;   
  public double balance;
}

并且还创建另一个类，它允许我输入多个帐户，将它们存储在数组列表中，然后确定哪个帐户拥有最大的余额。这是到目前为止我的代码:

import java.io.*;
import java.util.*;  //includes ArrayList
import java.text.*;  //for NumberFormat
public class BigBucks 
{     
  public static void main(String args[]) 
  {      
    NumberFormat formatter = NumberFormat.getNumberInstance( );
    formatter.setMinimumFractionDigits(2);   
    formatter.setMaximumFractionDigits(2);     
    String name;
    List aryLst = new ArrayList( ); 
    do         
    {            
      Scanner kbReader = new Scanner(System.in);  
      System.out.print("Please enter the name to whom the account belongs. (\"Exit\" to abort)"); 
      name = kbReader.nextLine( );
      if( !name.equalsIgnoreCase("EXIT") )   
      {
        System.out.print("Please enter the amount of the deposit. ");         
        double amount = kbReader.nextDouble();    
        System.out.println(" ");  //gives an eye-pleasing blank line 
        BankAccount myAccount = new BankAccount(name,amount);    
        aryLst.add(myAccount); //add account to array list    
      }        
    }while(!name.equalsIgnoreCase("EXIT"));
    //Search aryList and print out the name and amount of the largest bank account       
    BankAccount ba = aryLst.get(0);//get first account in the list    
    double maxBalance = ba.balance;    
    String maxName = ba.name;    
    for(int j = 1; j < aryLst.size( ); j++)  
    {
      //? Step through the remaining objects and decide which one has    
      //largest balance (compare each balance to maxBalance) 
      BankAccount na = aryLst.get(j);   
      double nBalance = na.balance;
      String nName = na.name;
      if(nBalance > maxBalance)
      {
        maxBalance = nBalance;
        maxName = nName;
      }

      //? Step through the remaining objects and decide which one has    largest balance (compare each balance to maxBalance)
      //?      
    }      
    System.out.println("The accouint with the largest balance belongs to "+ maxName + ".");
    System.out.println("The amount is $" + maxBalance + ".");
  }   
}

但是每次我编译它时都会出现此错误

Type mismatch: cannot convert from java.lang.Object to BankAccount

在第 28 和 35 行。为什么我会收到此错误以及如何修复它？？？如有任何帮助，我们将不胜感激。

Answer 1

您将 BankAccount 对象存储在一个普通列表中。

List aryLst = new ArrayList( );

更改它以指定 BankAccount 对象列表。

List<BankAccount> aryLst = new ArrayList<BankAccount>( );

当使用generics时这样，尝试将 BankAccount 以外的任何内容添加到列表中都会出现编译器错误，但在访问列表元素时不必强制转换对象。

<小时/>

另一种选择(如果您使用的是 Java 5 或更高版本，则不推荐)是在访问列表时强制转换对象。

BankAccount ba = (BankAccount)aryLst.get(0);