我需要使用instanceof与arraylist从不同的类

Question

您好我的问题是，我有一个arrayList与soccerPlayer和BaseballPlayer，但我需要寻找baseballPlayer并获得与highestBattingAvg的baseballPlayer我不知道如何使该方法可能这是我的BaseballPlayer类和我的MainClass ...谢谢

这是我BASEBALLPLAYER CLASS

package HomeWork7; 

public class BaseballPlayer extends Player{ 

    private int atBat, hits; 

    public BaseballPlayer(String sp, String t, String pos, 
      String f_name, String l_name, int ab, int h) { 
     super(sp, t, pos, f_name, l_name); 
     atBat = ab; 
     hits = h; 
    } 

    public double battingAverage() { 
     return ((double)hits/atBat); 
    } 

    public String toString() { 
     return super.toString() + " Position: " + super.getPos() 
     + " Batting Avg: " + String.format("%3.3f", battingAverage()); 
    } 
} 

THIS IS MY主类

package HomeWork7; 

import java.io.*; 
import java.util.*; 

public class PlayersMain 
{ 
    private ArrayList<Player> theplayer = new ArrayList<Player>(); 
    Scanner in; 
    PrintWriter out; 


    public void openFiles() 
    { 
    try 
     { 
      File input = new File("Players.txt"); 
      in = new Scanner(input); 

      File output = new File("output.txt"); 
      out = new PrintWriter(output);  
     } 
    catch (FileNotFoundException ex) 
     { 
     System.err.println("File not found!"); 
     ex.printStackTrace(); 
     } 
    } 

    public void readData() 
    { 
     String sport, team, pos, fn, ln; 
     int goalsScored; 
     int goalsAllowed; 
     int minutes; 
     int atBats; 
     int hits; 
     double innings; 
     int earnedRuns; 

     while(in.hasNext()) 
     { 
      sport = in.next(); 
      team = in.next(); 
      pos = in.next(); 
      fn = in.next(); 
      ln = in.next(); 

      if (sport.equalsIgnoreCase("soccer")) 
      { 
      minutes = in.nextInt(); 
      goalsScored = in.nextInt(); 

      if (pos.equalsIgnoreCase("goalie")) 
      { 
       goalsAllowed = in.nextInt(); 
       Goalie g = new Goalie(sport,team,pos,fn,ln,minutes,goalsScored,goalsAllowed); 
       theplayer.add(g); 
      } 
      SoccerPlayer socc = new SoccerPlayer(sport,team,pos,fn,ln,minutes,goalsScored); 
      theplayer.add(socc); 
      } 

      else if (sport.equalsIgnoreCase("Baseball")) 
      { 
       atBats = in.nextInt(); 
       hits = in.nextInt(); 

       if(pos.equalsIgnoreCase("Pitcher")) 
       { 
        innings = in.nextDouble(); 
        earnedRuns = in.nextInt(); 
        Pitcher pit = new Pitcher(sport,team,pos,fn,ln,atBats,hits,innings,earnedRuns); 
        theplayer.add(pit); 
       } 
       BaseballPlayer base = new BaseballPlayer(sport,team,pos,fn,ln,atBats,hits); 
       theplayer.add(base); 

      } 
     } 
    } 

    /** 
    * close the files that are been used in the program 
    * the output file and the input file 
    */ 
    public void closeFiles() 
    { 
    in.close(); 
    out.close(); 
    } 

    public BaseballPlayer getHighBattingAverage() 
    { 

    if(something instanceof BaseballPlayer) 
    { 
     //i do not know how to do this how to initialize this of something 
//and then make it work please i need help the array list already have the information 
//how i make it check from each one what is baseball player and what is not i know i need a for loop but i am stuck please help 
    } 

    } 

    public Goalie getLowestAvgGoalsAllowed() 
    { 
    return null; 

    } 

    public void displayPlayers(ArrayList<Player> list) 
    { 
     openFiles(); 

     for(Player e: list) 
     { 
      out.println(e.getPosition() + ": " + e.getName()); 
     } 

     closeFiles(); 
    } 
    public static void main(String[] args) { 
     PlayersMain pm = new PlayersMain(); 
     pm.openFiles();  //opens the input and output files 
     pm.readData();  //reads the data file and populates the arraylist 
     BaseballPlayer b = pm.getHighBattingAverage(); 
     System.out.println(b); 
     Goalie g = pm.getLowestAvgGoalsAllowed(); 
     System.out.println(g); 
     pm.displayPlayers(); //output all players in the arraylist to the file 
     pm.closeFiles();  //close input and output files 
    } 
} 

谢谢

Answer 1

增强for循环是你期望实现的。

for(Player player : theplayer) { 
    if(player instanceof BaseballPlayer) { 
     //put stuff here 
    } 
} 

Answer 2

我可以看到，你知道该怎么做的东西对每个对象的列表，如displayPlayers()。这听起来像你想对列表中的每个玩家做的事情就像是“检查这个玩家是否是迄今为止击球平均得分最高的BaseballPlayer，如果是，请记住该玩家。”

Answer 3

请参阅Martin8768's回答如何解决您的直接问题。您应该知道，使用instanceof不被视为非常面向对象，应尽可能避免。另一种方法需要你退一步考虑：

是否有类似的计算SoccerPlayer我能 概括？

，如果是这样，你可以创建Player一个抽象方法SoccerPlayer和BaseBallPlayer都可以有具体实现。然后，你可以简单地调用上播放该方法：

for(Player player : allPlayers) { 
    PlayerStatistics playerStats = player.calculatePlayerStatistics(); 
} 

通知增加了一个新的类型，PlayerStatistics - 可以用来存储在一个通用的方式有用的信息。