Question

此文件包含字符，字符串，整数和浮动数据类型。写一个具有以下功能的类：在循环中用户介绍数据类型（其中之一：char，String，int，double），in 响应应用程序打印。控制台所有值对应文件中存在的类型。

我知道如何打印所有数据类型。但我不知道用户在循环中如何引入数据类型。

我的代码：

package homework_3;

import java.io.*;
import java.util.Scanner;

public class Main2 {
    public static void main(String args[]) throws IOException {

        int i;
        double d;
        String str;
        char c;

        FileWriter fw = new FileWriter("test.txt");
        fw.write("Testing Scanner 10 12.2 one c b m");
        fw.close();

        FileReader fr = new FileReader("test.txt");
        Scanner sc = new Scanner(fr);

        while(sc.hasNext()) {
            if(sc.hasNextInt()) {
                System.out.println("int: " + sc.nextInt());
            } else if(sc.hasNextDouble()) {
                System.out.println("double: " + sc.nextDouble());
            } else {
            str = sc.next();
            if(str.length() == 1) {
                System.out.println("char: " + str);
            } else {
                System.out.println("String: " + str);
                }
            }
            fr.close();
        }
    }
}

Answer 1

创建一个数组（或地图）并将布尔值与所有类型相关联。将该数组的所有值初始化为False。然后读取您的文件，如果找到某种类型的数据，请将boolean关联设置为true。最后，打印与True值相关联的所有类型

    //Initialize your map with the types your looking for
    Map<String, Boolean> mapTypePresentInFile = new HashMap<String, Boolean>();

    //Set the values to false, because you didn't read your file yet
    mapTypePresentInFile.put("String", false);
    mapTypePresentInFile.put("Integer", false);
    mapTypePresentInFile.put("YourTypeHere", false);

    //Read your file and when you detect the use of a type set the type to true
    //I leave you the task to detect if a type is present
    mapTypePresentInFile.remove("YourTypeHere");
    mapTypePresentInFile.put("YourTypeHere", true);

    //Then you check in your map if the type has been set to true
    for(String type : mapTypePresentInFile.keySet()) {
        if(mapTypePresentInFile.get(type) == true) {
            System.out.println(type);
        }
    }

Java，在循环中从文件中获取数据类型

1 个答案: