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我的任务要求我制作一个犯罪记录程序，提示用户输入犯罪姓名、犯罪和定罪年份，然后它会使用另一个类（数据库）将其存储在一个数组中。该类如下所示： 

class Database { 
   String name;
   String crime;
   int year;
}

我做了一个方法来输入我的信息，但是当我测试它以显示列表时，它只显示了我输入的最后一个罪犯。为什么要这样做？

//method to input criminal records
public static void inputData() throws IOException {
    arr = new Database[3];        
    Database temp = new Database();        

    for(int i = 0; i < arr.length; i++){
        System.out.print("Enter criminal first and last name: ");
        String name = br.readLine();
        temp.name = name;        

        System.out.print("Enter crime: ");
        String crime = br.readLine();
        temp.crime = crime;

        System.out.print("Enter the year of conviction: ");
        int year = Integer.valueOf(br.readLine()).intValue();
        temp.year = year;

        // Copy the name, crime, year to the global variables
        arr[i] = temp;
        System.out.println(arr[i].name + " was convicted in the year " + arr[i].year + " for " + arr[i].crime + ".");
    }
}

我还需要根据用户输入的关键字（犯罪类型）进行顺序搜索，然后显示犯下该类型犯罪的罪犯。这是搜索的方法：

//method to search data
public static int searchData() throws IOException{
    System.out.print("Which crime would you like to select? (arson, theft, assault) ");
    String searchKey = br.readLine();

    for (int i = 0; i < arr.length; i++){
        if (arr[i].crime.equals(searchKey)){ 
            return i;  //found it!
        }
    }
    //key was not found
    return -1;
}

我的老师在解释方面很糟糕，所以我对顺序搜索进行了研究，但我仍然无法弄清楚如何让它显示犯下该罪行的罪犯名单。

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2 回答 2

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您正在添加对数组中同一实例的引用。您应该每次在循环内创建新实例：

// Database temp = new Database();   // Remove this

for(int i = 0; i < arr.length; i++) {
    Database temp = new Database();

此外，而不是直接访问中的字段Database：

temp.name = name;

您应该使用setters并将您的字段设为私有：

temp.setName(name);
于 2013-09-15T15:36:43.867 回答
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在本练习中，我建议您对罪行使用枚举，因此您可以添加应用程序将从用户输入中识别的其他罪行，如代码所解释的那样。

public enum Crime {
    ARSON{
        public String toString(){
            return "arson";
        }
    },
    ASSAULT{
        public String toString(){
            return "assault";
        }
    },
    THEFT{
        public String toString(){
            return "theft";
        }
    };

    public static String types(){
        return ARSON + ", " + ASSAULT + ", " + THEFT;
    }
}

我不会为罪犯使用数据库这个名称，因为它具有误导性。犯罪或非法更合适。

public class Outlaw {
    private String name;
    private Crime crime;
    private int year;

    public Outlaw(String name, Crime crime, int year){
        this.name=name;
        this.crime=crime;
        this.year=year;
    }
    public String getName() {
        return name;
    }
    public Crime getCrime() {
        return crime;
    }
    public int getYear() {
        return year;
    }
    @Override
    public String toString(){
        return new String(name + " was convicted in the year " + year + " for " + crime + ".");
    }
}

public class InputData {
    private static Scanner scanner;
    public static void main(String[] args) {
        scanner = new Scanner(System.in);
        List<Outlaw> criminals = inputData();
        showCriminals(criminals);
        showCriminalsForCrime(criminals);
        scanner.close();
    }
    public static List<Outlaw> inputData(){
        List<Outlaw> criminals = new ArrayList<Outlaw>();
        int numCriminals;

        System.out.print("How many criminals are you going to enter? ");
        numCriminals = scanner.nextInt(); scanner.nextLine();
        for(int i = 0; i < numCriminals; i++){
            criminals.add(inputOutlaw());
        }

        return criminals;
    }
    public static Outlaw inputOutlaw() {    
        System.out.print("Enter criminal first and last name: ");
        String name = scanner.nextLine();
        Crime crime = inputCrime();
        System.out.print("Enter the year of conviction: ");
        int year = scanner.nextInt(); scanner.nextLine();

        return new Outlaw(name, crime, year);
    }
    public static void showCriminalsForCrime(List<Outlaw> criminals){
        System.out.println("Search the criminals for their crime");
        Crime crime = inputCrime();
        List<Outlaw> criminalsForCrime = getCriminalsFor(crime,criminals);
        if(!criminals.isEmpty()){
            for(Outlaw criminal : criminalsForCrime){
                System.out.println(criminal.toString());
            }
        } else {
            System.out.println("There are not criminals for" + crime);
        }
    }
    public static Crime inputCrime(){
        Crime crime = null;

        while(crime == null){
            System.out.print("Which crime would you like to select? " + Crime.types() + ": ");
            try{
                crime = Crime.valueOf(scanner.nextLine().toUpperCase().trim());
            } catch(IllegalArgumentException e){
                System.out.println("The crime is not in the application!");
            }
        }

        return crime;
    }
    public static List<Outlaw> getCriminalsFor(Crime crime, List<Outlaw> criminals){
        List<Outlaw> criminalsForCrime = new ArrayList<Outlaw>();

        for(Outlaw criminal : criminals){
            if(criminal.getCrime().equals(crime)){
                criminalsForCrime.add(criminal);
            }
        }

        return criminalsForCrime;
    }
    public static void showCriminals(List<Outlaw> criminals){
        System.out.println("CRIMINALS: ");
        for(Outlaw criminal : criminals){
            System.out.println(criminal.toString());
        }
    }   
}

告诉你的老师解释得更好：D

于 2013-09-15T18:21:50.763 回答