循环遍历对象的 ArrayList 以查找最大值并返回详细信息 [英] Looping through ArrayList of object to find the highest value and return the details
本文介绍了循环遍历对象的 ArrayList 以查找最大值并返回详细信息的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我想创建一种方法来计算和显示最高的总体犯罪统计数据.例如输出如下内容:
I want to create a method which calculates and displays the highest overall crime stats. Eg to output something like:
*犯罪率最高的城市 204451 是纽约
*City with highest crime stats 204451 is New York
城市:纽约
州:纽约
人口:8165001
谋杀:596
抢劫:23511
攻击:26908
入室盗窃:22137
盗窃罪:115363
偷车:15936
暴力犯罪:51015
占有犯罪:153436*
Possession crime : 153436*
我有一个类 StartApp.java，它是 CityCrime 类型的 ArrayList，它从一个 csv 文件中读取犯罪统计数据:
I have one class StartApp.java which the ArrayList of CityCrime type, and it reads the crime stats from a csv file:
public static ArrayList<CityCrime> crimes = new ArrayList<CityCrime>();
public static void readCrimeData() {
File file = new File("crimeUSA.csv");
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.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]));
}
}
}
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 showMenu() {
Scanner menuSelect = new java.util.Scanner(System.in);
System.out.println("1. Display all crime stats by city");
System.out.println("2. Display all crime stats by selected city");
System.out.println("3. Display the murder stats by selected state ");
System.out.println("4. Display highest crime city - all crimes");
System.out.println("5. Display each state (in alphabetical order with the number of car thefts ");
System.out.println("6. Write / export all cities in descending order of Robbery rate ");
System.out.println("7. Quit");
System.out.println("Enter option 1-7");
//int option = menuSelect.nextInt();
Scanner scanner = new Scanner(System.in);
int option = Integer.parseInt(menuSelect.next());
switch(option) {
case 1:
displayAllCityCrimeStats();
break;
case 2:
System.out.println("Enter city");
String cityOption = menuSelect.next();
displayCityByName(cityOption);
break;
case 3:
System.out.println("Enter state");
String stateOption = menuSelect.next();
displayMurdersByState(stateOption);
break;
case 4:
//displayHighest();
displayCityHighestCrimeStats();
break;
case 5:
displayStateCarThefts();
break;
case 6:
return; // System.exit(0) or quit however you want to
default:
option = Integer.parseInt(scanner.next());
}
}
然后在 CityCrime.java 中我有:
Then in CityCrime.java I have:
public class CityCrime {
//Instance variables
private String city;
private String state;
private int population;
private int murder;
private int robbery;
private int assault;
private int burglary;
private int larceny;
private int motorTheft;
public int totalCrimes;
public static void main(String[] args) {
}
public int getTotalCrimes() {
return totalCrimes;
}
public int setTotalCrimes(int murder, int robbery, int assault, int burglary, int larceny, int motorTheft) {
this.totalCrimes = murder + robbery + assault + burglary + larceny + motorTheft;
return totalCrimes;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getState() {
return state;
}
public void setState(String state) {
if(state.equalsIgnoreCase("ALABAMA")) {
this.state = "AL";
}
//etc
}
public int getPopulation() {
return population;
}
public void setPopulation(int population) {
this.population = population;
}
public int getMurder() {
return murder;
}
public void setMurder(int murder) {
this.murder = murder;
}
public int getRobbery() {
return robbery;
}
public void setRobbery(int robbery) {
this.robbery = robbery;
}
public int getAssault() {
return assault;
}
public void setAssault(int assault) {
this.assault = assault;
}
public int getBurglary() {
return burglary;
}
public void setBurglary(int burglary) {
this.burglary = burglary;
}
public int getLarceny() {
return larceny;
}
public void setLarceny(int larceny) {
this.larceny = larceny;
}
public int getMotorTheft() {
return motorTheft;
}
public void setMotorTheft(int motorTheft) {
this.motorTheft = motorTheft;
}
public static void showAllMurderDetails() {
for (CityCrime crime : StartApp.crimes) {
System.out.println("Crime: City= " + crime.getCity() + ", Murder= " + crime.getMurder());
}
System.out.println();
}
public static int showAllViolentCrimes() {
int total = 0;
for(CityCrime crime : StartApp.crimes) {
total=total+crime.getMurder();
total=total+crime.getRobbery();
total=total+crime.getAssault();
}
System.out.println("Total of violent crimes: " + total);
return total;
}
public static int getPossessionCrimes() {
int total=0;
for (CityCrime crime : StartApp.crimes) {
total = total + crime.getBurglary();
total = total + crime.getLarceny();
total = total + crime.getMotorTheft();
}
System.out.println("Total of possession crimes: " + total);
return total;
}
}
到目前为止我已经尝试了很多不同的东西，但我似乎无法弄清楚，而且我已经深入谷歌页面.我真的很感激这个功能的帮助.我几乎明白为什么我尝试的方式不起作用，因为我写它时我知道它不会起作用.我尝试过的一些内容如下:(请尽量忽略它的混乱 - 我已经改变了 100 次)
I have tried a lot of different things so far but I just can't seem to figure it out, and I've been deep into the google pages. I'd really appreciate help with this function. I do almost understand why the way I'm trying is not working, as I write it I know it isn't going to work. A couple of what I've tried is the following: (please try to ignore the mess of it-I've changed things 100 times)
public static void displayHighest() {
int crimeStatCurrent = 0;
int crimeStatPrev = 0;
int crimeStatCurrent1 = 0;
int highest = 0;
String highestCity = "";
boolean flag;
CityCrime crimeStat = null;
for(CityCrime crime : crimes) {
/*
* crimeStatCurrent = crimeStatCurrent + crime.getAssault();; crimeStatCurrent =
* crimeStatCurrent + crime.getBurglary(); crimeStatCurrent = crimeStatCurrent +
* crime.getLarceny(); crimeStatCurrent = crimeStatCurrent +
* crime.getMotorTheft(); crimeStatCurrent = crimeStatCurrent +
* crime.getMurder(); crimeStatCurrent = crimeStatCurrent + crime.getRobbery();
*/
crimeStatCurrent = crime.setTotalCrimes(crime.getMurder(), crime.getRobbery(), crime.getAssault(), crime.getBurglary(), crime.getLarceny(), crime.getMotorTheft());
if(crime.getTotalCrimes() > crimeStatPrev) {
highest = crimeStatCurrent;
highestCity = crime.getCity();
System.out.println("Highest City" + highestCity);
}
}
}
public static void displayCityHighestCrimeStats() {
int crimeStat = 0;
int prevCrimeStat = 0;
int highestCrimeStat = 0;
int CurrentCrimeStat;
String highestCity = "";
int i;
for(CityCrime crime : crimes) {
/*
* crimeStat = crimeStat + crime.getAssault();; crimeStat = crimeStat +
* crime.getBurglary(); crimeStat = crimeStat + crime.getLarceny(); crimeStat =
* crimeStat + crime.getMotorTheft(); crimeStat = crimeStat + crime.getMurder();
* crimeStat = crimeStat + crime.getRobbery();
*/
//crimeStat = crime.setTotalCrimes(crime.getMurder(), crime.getRobbery(), crime.getAssault(), crime.getBurglary(), crime.getLarceny(), crime.getMotorTheft());
for(i = 0; i < crimes.size(); i++) {
if(crime.setTotalCrimes(crime.getMurder(), crime.getRobbery(), crime.getAssault(), crime.getBurglary(), crime.getLarceny(), crime.getMotorTheft()) > prevCrimeStat) {
highestCity = crime.getCity();
highestCrimeStat = crime.getTotalCrimes();
}
else if(crime.setTotalCrimes(crime.getMurder(), crime.getRobbery(), crime.getAssault(), crime.getBurglary(), crime.getLarceny(), crime.getMotorTheft()) < prevCrimeStat) {
}
prevCrimeStat = crimeStat;
}
System.out.println("Crime Stat: " + crimeStat + "for " + crime.getCity());
}
//System.out.println("City with highest crime stats is " + highestCity + " with " + crimeStat);
}
好的，这就是我现在的方法:
Okay, this is the method I have now:
public CityCrime highestCrimeCity(List<CityCrime> cities) {
return cities
// Create a stream from the list of cities
.stream()
// Sort by totalCrime in reverse order
.sorted(Comparator.comparingInt(CityCrime::getTotalCrimes).reversed()
// Take the first city if it exists (you could pass an empty array)
.findFirst()
// If the city exists return it, otherwise null
.orElseNull();
}
对于FindFirst"，我收到错误消息:未定义类型 Comparator 的 findFirst() 方法
for 'FindFirst' I am getting the error: The method findFirst() is undefined for the type Comparator
非常感谢所有帮助/评论.
Really appreciate all help/comments.
推荐答案
我的建议是保持干净的代码:
My tip is to maintain a clean code:
- 代码的每个方法都应该解决一个任务.以前从未见过代码的人也会更容易阅读和维护代码
- 尝试使用记录器而不是 System.out 方法.这为您提供了更大的灵活性
- 尽可能使用现有的方法，而不是重写它们.不要重新发明轮子
- 尝试使用new"(不是很新，它在 Java 8 中出现)可能的话流构造.代码将更易于阅读和维护
- 尽可能不要使用实例变量，而是将数据作为参数传递.代码将更容易理解，并且受副作用的影响更小
特别是你可以这样做:
// This method just calculate the City with highest crime (single task)
// It takes cities as a parameter, no other data are needed (pass parameters instead of using instance variables)
// It uses stream of java 8 (prefer using stream over loops)
// It uses sorted method (use existing methods when possible)
// It uses Optional
public CityCrime highestCrimeCity(List<CityCrime> cities) {
return cities
// Create a stream from the list of cities
.stream()
// Sort by totalCrime in reverse order
.sorted(Comparator.comparingInt(CityCrime::getTotalCrime).reversed()
// Take the first city if it exists (you could pass an empty array)
.findFirst()
// If the city exists return it, otherwise null
.orElseNull();
}
您可以调用它来打印输出，如下所示:
Than you can call it to print the output as follow:
CityCrime badCity = highestCityCrime(cities);
System.out.println("The baddest city is " + badCity.getCity() + " with " + badCity.getTotalCrimes() + " crimes");
当您配置记录器时，您可以将 System.out.println 替换为 LOGGER.info
When you configured a logger you can replace the System.out.println with LOGGER.info
这篇关于循环遍历对象的 ArrayList 以查找最大值并返回详细信息的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
查看全文
