Question

有可能做这样的事吗？假设我想在CountriesTest中添加我赋予值的值，并将它们添加到Countries中的ArrayList。另外我如何引用aCountries打印选项2，看到我在选项1中创建它我无法在其他地方访问它。

这是我的界面

public interface CountriesInterface
{
    public String largestPop();
    public String largestArea();
    public String popDensity();
}

这是国家类

import java.util.*;
public class Countries implements CountriesInterface
{
    private final List<CountriesInterface> theCountries = new ArrayList<>();
    private String cName;
    private String finalPopName;
    private String finalAreaName;
    private String finalDensityName;
    private int cPop = 0;
    private int cArea = 0;
    private int popDensity = 0;
    private int popCounter = 0;
    private int areaCounter = 0;
    private int densityCounter = 0;
    public Countries(String cName, int cPop, int cArea, int popDensity)
    {
        this.cName = cName;
        this.cPop = cPop;
        this.cArea = cArea;
        this.popDensity = popDensity;
    }

    public String largestPop()
    {
        for(int i = 0; i < theCountries.size(); i++)
        {
            if(cPop > popCounter)
            {
                popCounter = cPop;
                finalPopName = cName;
            }    
        }
        return finalPopName;
    }

    public String largestArea()
    {
        for(int i = 0; i < theCountries.size(); i++)
        {
            if(cArea > areaCounter)
            {
                areaCounter = cArea;
                finalAreaName = cName;
            }    
        }
        return finalAreaName;
    } 

    public String popDensity()
    {
        for(int i = 0; i < theCountries.size(); i++)
        {
            if(popDensity > densityCounter)
            {
                densityCounter = popDensity;
                finalDensityName = cName;
            }    
        }
        return finalDensityName;
    } 

}

这是CountriesTest类

import java.util.*;
public class CountriesTest
{
    public static void main(String[] args)
        {             
            int population = 0;
            int area = 0;
            int density = 0;
            Scanner myScanner = new Scanner(System.in);            
            boolean done = false;
            do
            {
                System.out.println("1.  Enter a country \n2.  Print countries with the largest population, area, and population density \n3.  Exit");
                int choice = Integer.parseInt(myScanner.nextLine());
                if (choice == 1)
                {
                    System.out.print("Enter name of country: ");
                    String input1 = myScanner.nextLine();
                    System.out.print("Enter area of country in square kilometers: ");
                    String input2 = myScanner.nextLine();
                    population = Integer.parseInt(input2);
                    System.out.print("Enter population of country: ");
                    String input3 = myScanner.nextLine();
                    area = Integer.parseInt(input3);
                    density = population/area;
                    Countries aCountries = new Countries(input1, population, area, density);
                }
                else if(choice == 2)
                {
                    System.out.println("The country with the largest population: " );
                    System.out.println("The country with the largest area: "  );
                    System.out.println("The country with the largest population density is: "  );
                }
                else if(choice == 3)
                {
                     done = true;
                }              
                else
                    System.out.println("Invalid Choice");     
            }
            while (!done);
           System.exit(0);
        }
}

Answer 1

好的，您的代码中存在一些混淆。

您正在使用＆＃34;国家＆＃34;同时为某个国家/地区和国家/地区列出课程。我不会推荐它，但至少你应该做出静态＆＃34;用于国家清单的成员和方法。或者您可以声明List theCountries = new ArrayList＆lt;＆gt;（）;而在主方法内部。
您永远不会添加新的＆＃34;国家＆＃34;反对国家名单。所以，如果您已经在主要方法中声明了国家，那么只需使用＆＃34; theCountries.add（aCountries）＆＃34;紧接着＆＃34;新国家（...）＆＃34;。
您的搜索方法（如largestPop）不会起作用，因为他们从不搜索＆＃34; theCountries＆＃34;的内容。数组列表。（＆＃34; i＆＃34;变量只是遍历索引，但从未实际用于从此ArrayList获取一个位置）。
和btw，不需要System.exit（0）（暗示）

发出从不同的类向ArrayList添加元素的问题

1 个答案: