Hashmap - 返回键并将其设置为 object 的值

Question

I have two CSV files, one "crimeUSA.csv" with the headers state , city , population etc. and one StatesAbbreviations with the headers states, abbrev . First I read the "crimeUSA.csv" file and create CityCrime objects.

Instead of using the state in this file, I want to match it with the state in the StatesAbbreviations file and set the state as the appropriate abbreviation value instead. I previously had the states and matching abbreviations hardcoded in the setter for state but I have removed it as was pretty long and ugly. In the readCrimeData() method is where I am creating the instances of the CityCrime object, so crime.setState(stats[1]); is commented out as I do not wanted the state/abbreviation hardcoded anymore.

This is the StartApp class:

public static void main(String[] args) {

        try {
            CityCrime.readAbbrevData();
            readCrimeData("crimeUSA.csv");
            System.out.println("Total cities read: " + getTotalCities());
            showMenu();
        } catch (Exception e) {

            e.printStackTrace();
        }
    }
    
    /**
     * Reads the crime data for each city from entered file
     * Adds the CityCrime objects to the crimes ArrayList
     */
    public static void readCrimeData(String fromFile) {

        File file = new File(fromFile);

        FileReader fileReader;
        BufferedReader bufferedReader;
        
        String crimeInfo;
        String[] stats;
        try {
            fileReader = new FileReader(file);
            bufferedReader = new BufferedReader(fileReader);

            crimeInfo = bufferedReader.readLine();
            crimeInfo = bufferedReader.readLine();

            do {
                CityCrime crime = new CityCrime(); // Default constructor
                stats = crimeInfo.split(",");
                {
                    if (stats[0] != null) {
                        crime.setCity(stats[0]);
                    }
                    if (stats[1] != null) {
                        crime.setAbbreviation(stats[1]);
                        //crime.setState(stats[1]);
                    }
                    if (stats[2] != null) {
                        if (Integer.parseInt(stats[2]) >= 0) {
                            crime.setPopulation(Integer.parseInt(stats[2]));
                        }
                    }
                    if (stats[3] != null) {
                        if (Integer.parseInt(stats[3]) >= 0) {
                            crime.setMurder(Integer.parseInt(stats[3]));
                        }
                    }

                    if (stats[4] != null) {
                        if (Integer.parseInt(stats[4]) >= 0) {
                            crime.setRobbery(Integer.parseInt(stats[4]));
                        }
                    }

                    if (stats[5] != null) {
                        if (Integer.parseInt(stats[5]) >= 0) {
                            crime.setAssault(Integer.parseInt(stats[5]));
                        }
                    }

                    if (stats[6] != null) {
                        if (Integer.parseInt(stats[6]) >= 0) {
                            crime.setBurglary(Integer.parseInt(stats[6]));
                        }
                    }

                    if (stats[7] != null) {
                        if (Integer.parseInt(stats[7]) >= 0) {
                            crime.setLarceny(Integer.parseInt(stats[7]));
                        }
                    }

                    if (stats[8] != null) {
                        if (Integer.parseInt(stats[8]) >= 0) {
                            crime.setMotorTheft(Integer.parseInt(stats[8]));
                        }
                    }
                    crime.setTotalCrimes(Integer.parseInt(stats[3]), Integer.parseInt(stats[4]), Integer.parseInt(stats[5]), Integer.parseInt(stats[6]), Integer.parseInt(stats[7]), Integer.parseInt(stats[8]));
                }
                crimes.add(crime);
                System.out.println(crime);

                crimeInfo = bufferedReader.readLine();

            } while (crimeInfo != null);

            fileReader.close();
            bufferedReader.close();

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (NumberFormatException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }
    
    public static void readAbbrevData() {

        File file = new File("StatesAbbreviations.csv");
        var stateToAbbreviation = new HashMap<String, String>();
        
        try (BufferedReader bufferedReader = new BufferedReader(new FileReader(file))) {
            String abbrevInfo;
            while ((abbrevInfo = bufferedReader.readLine()) != null) {
                String[] stats = abbrevInfo.split(",");
                // stats[0] may be empty, but never null, no check required
                stateToAbbreviation.put(stats[0], stats[1]);
            }
        } catch (IOException e) {
            throw new RuntimeException("Could not read state / abbreviations from CSV file", e);
        }
        
        for (String key: stateToAbbreviation.keySet()){
            System.out.println(key +" = "+stateToAbbreviation.get(key));
        }
    }

The CityCrime class:

    public static void main(String[] args) {
        
        
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getState() {
        return state;
    }
    
    public void setState(String state) {
        this.state = state;
    }


    public int getPopulation() {
        return population;
    }


    public void setPopulation(int population) {
        this.population = population;

    }
    //etc
    

    @SuppressWarnings("null")
    public String setAbbreviation(String state) {
        return stateToAbbreviation.getOrDefault(state,"UNKNOWN");
        }

My aim is to have a setAbbreviation, so it takes the state value of the CityCrime CSV, basically matches it with the state in the StatesAbbreviation class, and sets it as the matching abbreviation. As you can probably tell, I am relatively new to Java, so please try and explain in simple terms as possible to help my understanding.

Answer 1

Change the return type of your readAbbrevData method from void to Map<String,String> to return a map instead of just printing it out to console, ie:

public static Map<String,String> readAbbrevData() {
    File file = new File("StatesAbbreviations.csv");
    var stateToAbbreviation = new HashMap<String, String>();

    // ....
   return stateToAbbreviation
}

Call the above method before processing your crime data file in your readCrimeData method to get the map and use it to set your abrivations

public static void readCrimeData(String fromFile) {

    Map<String,String> myMap = readAbbrevData();
    File file = new File(fromFile);
    ....


       if (stats[1] != null) {
             crime.setAbbreviation(myMap.get(stats[1]));
            //crime.setState(stats[1]);
       }