数据结构文件输入输出

Question

我正在尝试编写一个使用 ArrayLists 和文件输入输出的简单程序的程序。该程序应读取文本文件并将每个字段存储在数组列表中，然后执行计算。该文件包含城市名称、人口和国家名称。即（伦敦，7500000，英国）当我运行带有命令行参数的程序时，它应该打印语句说明有多少城市的人口大于命令行参数。

我希望有人能指导我正确的方向。谢谢。

Answer 1

没有给出'ready to run'答案，我认为它应该是这样的（伪代码）

  public static void main(String[] args) {
    convert first argument to integer
    set up a reader for your file
    while (another line is found) {
      split the line by comma
      convert second item in array to an integer
      if integer >= integer passed in args
              print current line
    }
  }

请记住，您必须进行异常处理（IOExceptions、NumberFormatException 等）。我故意不包括保存到数组列表，因为这意味着你必须循环两次（一次遍历文件，一次遍历列表）这是没有必要的。

Answer 2

这是一个很好的学校练习:-)

假设您在 C:\temp\cities.txt 中的输入文件包含：

London,83000000,UK
Paris,22000000,France
Madrid,32000000,Spain

以下classTest.java：

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;

public class Test {

  private static ArrayList<City> loadDataFromFile() throws IOException {

    ArrayList<City> list = new ArrayList<City>();
    BufferedReader br = null;
    String sCurrentLine;
    br = new BufferedReader(new FileReader("C:\temp\cities.txt"));

    while ((sCurrentLine = br.readLine()) != null) {
      String[] splittedLine = sCurrentLine.split(",");
      City city = new City(splittedLine[0], Integer.parseInt(splittedLine[1]), splittedLine[2]);
      list.add(city);
    }

    br.close();
    return list;
  }

  public static void main(String[] args) throws IOException {

    ArrayList<City> list = loadDataFromFile();
    int input = Integer.parseInt(args[0]);
    Iterator<City> it = list.iterator();

    while (it.hasNext()) {
      City currentCity = it.next();
      if (currentCity.getPopulation() > input) {
        System.out.println("Cities with population greater than " + input + " : " + currentCity.getName() + "," + currentCity.getCountry());
      } else if (currentCity.getPopulation() == input) {
        System.out.println("City with population equals to " + input + " : " + currentCity.getName() + "," + currentCity.getCountry());
      } else {
        System.out.println("Cities with population lower than " + input + " : " + currentCity.getName() + "," + currentCity.getCountry());
      }
    }

  }
}

和一个简单的 POJO :

public class City {

  private String name;

  private int population;

  private String country;

  public City(String name, int population, String country) {
    this.name = name;
    this.population = population;
    this.country = country;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public int getPopulation() {
    return population;
  }

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

  public String getCountry() {
    return country;
  }

  public void setCountry(String country) {
    this.country = country;
  }

}

会给你：

java Test 3200000

Cities with population greater than 32000000 : London,UK
Cities with population lower than 32000000 : Paris,France
City with population equals to 32000000 : Madrid,Spain

数据结构文件输入输出

Data structure file input output

java

oop

io

file-io

object