如何从java中的文本文件中读取您的输入

Question

I'm sort of new to java and i have this lexical analyzer program for my assignment, the program works fine and my only problem is my input needs to come from a text file.

public class LexicalAnalyzer {

public static void main(String[] args) {

   Scanner reader = new Scanner(System.in);
   System.out.println("Input strings: ");
   String str = reader.nextLine();

   for (int i = 0; i < str.length(); i++)
   {
       switch (str.charAt(i))
       {
           case '+':
                System.out.println("Token: +   Type: ADDITION");
                break;
           case '-':
                System.out.println("Token: -   Type: SUBTRACTION");
                break;
           case '*':
                System.out.println("Token: *   Type: MULTIPLICATION");
                break;
           case '/':
                System.out.println("Token: /   Type: DIVISION");
                break;
           case '(':
                System.out.println("Token: (   Type: LEFT PARENTHESIS");
                break;
           case ')':
                System.out.println("Token: )   Type: RIGHT PARENTHESIS");
                break;
           case '=':
                System.out.println("Token: =   Type: EQUALS");
                break;
           case ';':
                System.out.println("Token: ;   Type: END");
                break;
           case '0':
                System.out.println("Token: 0   Type: NUM");
                break;
           case '1':
                System.out.println("Token: 1   Type: NUM");
                break;
           case '2':
                System.out.println("Token: 2   Type: NUM");
                break;
           case '3':
                System.out.println("Token: 3   Type: NUM");
                break;
           case '4':
                System.out.println("Token: 4   Type: NUM");
                break;
           case '5':
                System.out.println("Token: 5   Type: NUM");
                break;
           case '6':
                System.out.println("Token: 6   Type: NUM");
                break;
           case '7':
                System.out.println("Token: 7   Type: NUM");
                break;
           case '8':
                System.out.println("Token: 8   Type: NUM");
                break;
           case '9':
                System.out.println("Token: 9   Type: NUM");
                break;   
       }
   }      

Any ideas on how i can read my input from a text file?

Answer 1

You can use below utility methods from File class to read file contents.

Files.readAllLines() or Files.lines()

Answer 2

Look at this https://www.mkyong.com/java/how-to-read-file-from-java-bufferedreader-example/ it's so easy

read the file as lines and split every line to accomplish your mession

there are many ways to read from file such as using buufererdReader as example

i think it's an easy question you should do some search before asking any question on stackoverflow

hope it ll be useful for you

Answer 3

I am giving you the program for reading from text file.

Here is the code

public class ReadToFile {

    public static void main(String[] args) {
        try {
            //File file = new File("C:\\Sample\\ketan.txt");
            FileReader fileReader = new FileReader("C:\\Sample\\xyz.txt");
            BufferedReader bufferedReader = new BufferedReader(fileReader);
            String content = bufferedReader.readLine();
            System.out.println("Content of file is " + content);
            bufferedReader.close();

        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}