Question

我正在为用户编写一个程序，将一个字符串添加到ArrayList然后显示它。它不起作用，似乎compareTo()存在问题。

这是我的代码：

public class database {

    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static String country[] = new String[100];
    static String capital[] = new String[100];
    static double population[] = new double[100];
    static List<String> countriesList = Arrays.asList(country);

    public static void main(String args[]) throws IOException {
        country[0] = "Barbados";
        country[1] = "France";
        country[2] = "Nigeria";
        country[3] = "USA";
        country[4] = "Japan";
        capital[0] = "Bridgetown";
        capital[1] = "Paris";
        capital[2] = "Abuja";
        capital[3] = "Washington";
        capital[4] = "Tokyo";
        population[0] = 65.3;
        population[1] = 315.8;
        population[2] = 170.1;
        population[3] = 2840;
        population[4] = 126.7;

    public static void searchCountry() throws IOException {
        Scanner in = new Scanner(System.in);
        String output;
        int size, i;
        System.out.println("Search Country:");
        output = br.readLine();
        boolean found = false;
        for (i = 0; i < country.length; i++)
            if (output.compareTo(country[i]) == 0) {
                found = true;
                break;
            }
        if (found)
            System.out.println(output + " is found at index " + i);
        else
            System.out.println(output + "Country not found, choose Add country to add it");

    public static void listCountry() throws IOException {
        for (String c : countriesList) {
            if (!=null)
            System.out.println(c);

        }
    }
}

我的代码末尾的null也存在问题。

Answer 1

编写代码时，最好从头开始。即。

首先，编写类名并确保括号

没有问题

public class MyClass{
}

然后，在其中编写main方法。

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

然后，编写您的方法，并在main方法中进行测试。

public class MyClass{
    public void mymethod(){
        //do something
        System.out.println("say something");
    }
    public static void main(String[] args){
         MyClass mc = new MyClass();
         mc.mymethod();
    }
}

如果你试图在一个镜头中写下所有东西它就不会起作用，如果你不是专家那么你就很难解决问题。

Answer 2

您无法在方法中编写方法。在打开main()

searchCountry()

您不会检查任何内容为null。也许你的意思是if(c != null)

只要这样写，你应该没问题：

public class database {

    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static String country[] = new String[100];
    static String capital[] = new String[100];
    static double population[] = new double[100];
    static List<String> countriesList = Arrays.asList(country);

    public static void main(String args[]) {
        country[0] = "Barbados";
        country[1] = "France";
        country[2] = "Nigeria";
        country[3] = "USA";
        country[4] = "Japan";
        capital[0] = "Bridgetown";
        capital[1] = "Paris";
        capital[2] = "Abuja";
        capital[3] = "Washington";
        capital[4] = "Tokyo";
        population[0] = 65.3;
        population[1] = 315.8;
        population[2] = 170.1;
        population[3] = 2840;
        population[4] = 126.7;
        searchCountry();
        listCountry();
    }

    public void searchCountry() throws IOException {
        Scanner in = new Scanner(System.in);
        String output;
        int size, i;
        System.out.println("Search Country:");
        output = br.readLine();
        boolean found = false;
        for (i = 0; i < country.length; i++)
            if (output.compareTo(country[i]) == 0) {
                found = true;
                break;
            }
        if (found)
            System.out.println(output + " is found at index " + i);
        else
            System.out.println(output + "Country not found, choose Add country to add it");
    }

    public void listCountry() {
        for (String c : countriesList) {
            if (c!=null)
                System.out.println(c);
        }
    }
}

Answer 3

您忘记了c中的c != null。
您无法在java中定义方法内部的方法。
另外，在测试equals相等时使用String方法，即if (output.equals(country [i]))。

将字符串添加到集合并显示它

3 个答案: