如何检查文件是否包含用户输入的特定号码？ （Java）的

Question

您好我正在尝试编写一个程序来检查指定文件中是否有用户输入的数字，但是如果该文件中没有该编号，我希望程序循环回到开头，我怎么能这样做？

这是我到目前为止所做的混乱：

import java.util.Scanner;

public class Classtest2 {
    public static void main(String[] args) {

    //    //1. class
    Scanner sc = new Scanner(Classtest2.class.getResourceAsStream("trombones.txt"));
    Scanner myScanner = new Scanner(System.in);

    System.out.println("What number would you like to check for?");
    String number = myScanner.nextLine() ;
    String keyWord = number, word;
    int lineNum = 0;

    while(sc.hasNextLine()) {
        word = sc.next();

        if(word.equals(myScanner.nextLine().trim())) {
            System.out.println("The number "+number+ " is there");

            break;
        } else {
            // not found
        }
    } // main
} // class

Answer 1

你需要做的就是从用户那里获取输入，然后检查它是否存在于文件中。你不应该在循环中使用myScanner.nextLine().trim()因为它等待每个循环时间获得用户输入。你从用户那里得到一个号码，你应该在文件中检查它。你做的是得到用户输入然后再等待用户一次又一次地输入值

固定代码

   import java.util.Scanner;

    public class Classtest2 {
        public static void main(String[] args) {

        //    //1. class
        Scanner sc = new Scanner(Classtest2.class.getResourceAsStream("trombones.txt"));
        Scanner myScanner = new Scanner(System.in);

        System.out.println("What number would you like to check for?");
        String number = myScanner.nextLine() ;
        int lineNum = 0;

        while(sc.hasNextLine()) {
            word = sc.next();

            if(word.equals(number.trim())) { //here was the problem
                System.out.println("The number "+number+ " is there");

                return;
            } else {

            }
        } 
        System.out.println("not found");  // not found
    } 

最好的方法

import java.util.Scanner;

public class Classtest2 {

    public static void main(String[] args) {

        Scanner myScanner = new Scanner(System.in);
        System.out.println("What number would you like to check for?");
        String number = myScanner.nextLine();
        if(isFound(number)){
            System.out.println("The number "+number+ " is there");
        }else{
            System.out.println("The number "+number+ " doesn't exist");
        }
    }

    public static boolean isFound(String number) {

        Scanner sc = new Scanner(Classtest2.class.getResourceAsStream("trombones.txt"));
        String word="";
        while (sc.hasNextLine()) {
            word = sc.next();

            if (word.equals(number.trim())) { 
                return true;
            }
        }
        return false;
    }
}

Answer 2

这对我有用，希望对你有用：

package test;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.Scanner;

public class Classtest2 {

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

        File f = new File("trombones.txt");
        f.createNewFile();
        Scanner myScanner = new Scanner(System.in);
        boolean numExiste = menu(new Scanner(f), myScanner);
        while (!(numExiste)){
            numExiste = menu(new Scanner(f), myScanner);
        }
        myScanner.close();

    }

    private static boolean menu(Scanner fileScanner, Scanner myScanner) throws FileNotFoundException{
        String word = "";
        System.out.println("What number would you like to check for?");
        String number = myScanner.nextLine().trim();

        while(fileScanner.hasNextLine()){
            word = fileScanner.nextLine();
            if(word.trim().equals(number)){
                System.out.println("The number "+number+ " is there");
                return true;
            }else{
                //Not the number
            }
        }
        System.out.println("The number "+ number+ " is not in the file\n\n");
        return false;

    }
} // main } // class