我用Java编写了以下程序,它将文本文件的内容读取到 HashMap 用户需要一年的时间才能返回当年赢得世界大赛的球队以及该球队赢得世界大赛的次数。我成功地构建了 哈希图 但我在努力想我该怎么做 哈希图 在程序的主驱动程序方法中可访问(我理解为什么它不可访问,我正在寻找如何访问它)。现在,实例化 哈希图 在main方法中为空。我已经在这个问题上纠结了一段时间,似乎找不到办法来解决这个问题。如有任何见解,将不胜感激!

import java.io.*; // contains all classes used in file processing
import java.io.File; // allows program to gather file information
import java.io.FileNotFoundException;

import java.util.*;
import java.util.Scanner; // allows program to get user input

public class Program3 {

    public void processFile(String filename)
    {
        // pass filename as arg to File class
        File worldSeries = new File("Program3.txt");

        // Create a Scanner object
        Scanner scan;

        // Create String line variable to read each line
        String line = "";

        try {
            // HashMap which tracks each year's World Series Winner
            HashMap<Integer,String> yearWinner = new HashMap<Integer,String>();
            // HashMap which tracks the number of times each team wins the World Series
            HashMap<String,Integer> numWins = new HashMap<String,Integer>();

            // Set startYear
            int startYear = 1903;

            // Pass filename to Scanner object
            scan = new Scanner(worldSeries);

            // Check for another line in input to scan
            while(scan.hasNextLine()){
                // Skip years during which the WorldSeries was not played
                if(startYear == 1904 || startYear == 1994) {
                    startYear++;
                }
                line = scan.nextLine(); // reads nextLine of String data type
                yearWinner.put(startYear, line); //  inserts a mapping into a HashMap
                if(numWins.containsKey(line)) { // checks if a key is mapped into the HashMap or not
                    numWins.put(line, numWins.get(line)+1); // if key exists, increment numWins value
                }else {
                    numWins.put(line,1); // if key does not exist, set numWins to 1
                }
                startYear++; // increment year
            }
            //testing for some case
            System.out.println(yearWinner.get(1905));
            System.out.println(numWins.get("New York Yankees"));
        } catch (FileNotFoundException e) {
            System.out.println("File not found");
        }
    }
    /*
    collectInput - method to collect user input for the year.
     */
    public int collectInput() {
        Scanner in = new Scanner(System.in); // Scanner object to read user input.

        int year; // declare year
        System.out.print("Please enter a year between 1903 & 2020: ");
        year = in.nextInt(); // collect the user input

        // check the year is either 0(sentinel value) or within range 1903 and 2020.
        while (year != 0 && (year < 1903 || year > 2020)) {
            // otherwise collect a valid year.
            System.out.print("Year is invalid! Please enter a year between 1903 & 2020: ");
            year = in.nextInt();
        }

        return year; // return the year.
    }
    /*
    displayOutput - method gets the user input and displays the output.
    @param winners - class instance
    @param yearWinner - map which stores year and team
    @param winsMap - map which stores team and number of wins
     */
    public void displayOutput(Program3 winners, HashMap<Integer, String> yearWinner, HashMap<String, Integer> numWins) {

        // loop the input until sentinel value is entered
        while (true) {

            // call the method to collect input from user
            int year = collectInput();

            // validate for sentinel value
            if (year == 0) {
                System.out.println("Thank you, goodbye!");
                return; // end program
            }

            // get the winning team for the given year.
            String winningTeam = winners.getWinningTeamForYear(year, yearWinner);

            // if there is winning team for the given year..
            if (winningTeam != null) {
                // get the number of wins of that team between 1903 and 2020.
                int numOfWins = winners.getNumberOfWins(winningTeam, numWins);
                // display the winning team and number of wins.
                System.out.println("The winning for the Year " + year + " is: " + winningTeam);
                System.out.println("Number of Wins secured by team: " + winningTeam + " is " + numOfWins);
            }
        }
    }
    // pass the year and get the winning team
    public String getWinningTeamForYear(int year, HashMap<Integer, String> yearWinner) {
        // if there is an entry for the given year.. to validate excluded years
        if (yearWinner.containsKey(year)) { // if yearWinner containsKey
            return yearWinner.get(year); // return the winning team
        }
        else {
            // display the message and return null.
            System.out.println("World Series not held in " + year);
            return null;
        }
    }

    // pass the team name in the hashmap and get the number of wins
    public int getNumberOfWins(String winningTeam, HashMap<String, Integer> numWins) {
        return numWins.get(winningTeam);
    }

    public static void main(String[] args) {

        HashMap<Integer, String> yearWinner = new HashMap<>(); // hashmap to store year and winners.
        HashMap<String, Integer> numWins = new HashMap<>(); // hashmap to store winners and number of wins.

        String fileName = "Program3.txt"; // file name where the data is stored.
        // You can also use full path of file Ex. E:\\InputFiles\\Program3.txt (\\ delimiter slash indicating \)

        Program3 winners = new Program3();
        winners.processFile("Program3.txt");
        System.out.println(yearWinner);
        winners.displayOutput(winners, yearWinner, numWins); // non static method to collect user input and display output.

    }
}

Program3.txt 从中 哈希图 正在建造:

Boston Americans
New York Giants
Chicago White Sox
Chicago Cubs
Chicago Cubs
Pittsburgh Pirates
Philadelphia Athletics
Philadelphia Athletics
Boston Red Sox
Philadelphia Athletics
Boston Braves
Boston Red Sox
Boston Red Sox
Chicago White Sox
Boston Red Sox
Cincinnati Reds
Cleveland Indians
New York Giants
New York Giants
New York Yankees
Washington Senators
Pittsburgh Pirates
St. Louis Cardinals
New York Yankees
New York Yankees
Philadelphia Athletics
Philadelphia Athletics
St. Louis Cardinals
New York Yankees
New York Giants
St. Louis Cardinals
Detroit Tigers
New York Yankees
New York Yankees
New York Yankees
New York Yankees
Cincinnati Reds
New York Yankees
St. Louis Cardinals
New York Yankees
St. Louis Cardinals
Detroit Tigers
St. Louis Cardinals
New York Yankees
Cleveland Indians
New York Yankees
New York Yankees
New York Yankees
New York Yankees
New York Yankees
New York Giants
Brooklyn Dodgers
New York Yankees
Milwaukee Braves
New York Yankees
Los Angeles Dodgers
Pittsburgh Pirates
New York Yankees
New York Yankees
Los Angeles Dodgers
St. Louis Cardinals
Los Angeles Dodgers
Baltimore Orioles
St. Louis Cardinals
Detroit Tigers
New York Mets
Baltimore Orioles
Pittsburgh Pirates
Oakland Athletics
Oakland Athletics
Oakland Athletics
Cincinnati Reds
Cincinnati Reds
New York Yankees
New York Yankees
Pittsburgh Pirates
Philadelphia Phillies
Los Angeles Dodgers
St. Louis Cardinals
Baltimore Orioles
Detroit Tigers
Kansas City Royals
New York Mets
Minnesota Twins
Los Angeles Dodgers
Oakland Athletics
Cincinnati Reds
Minnesota Twins
Toronto Blue Jays
Toronto Blue Jays
Atlanta Braves
New York Yankees
Florida Marlins
New York Yankees
New York Yankees
New York Yankees
Arizona Diamondbacks
Anaheim Angels
Florida Marlins
Boston Red Sox
Chicago White Sox
St. Louis Cardinals
Boston Red Sox
Philadelphia Phillies
New York Yankees
San Francisco Giants
St. Louis Cardinals
San Francisco Giants
Boston Red Sox
San Francisco Giants
Kansas City Royals
Chicago Cubs
Houston Astros
Boston Red Sox
Washington Nationals
Los Angeles Dodgers