How to detect EOF in Java?

问题

I've tried some ways to detect EOF in my code, but it still not working. I've tried using BufferedReader, Scanner, and using char u001a to flag the EOF, but still not make any sense to my code. Here is my last code :

    Scanner n=new Scanner(System.in);
    String input;
    int counter=0;

    while(n.hasNextLine())
    {
        input=n.nextLine();
        char[] charInput=input.toCharArray();
        for (int i = 0; i < input.length(); i++) {
            if(charInput[i]=='"')
            {
                if(counter%2==0)
                {
                    System.out.print("``");
                }
                else
                {
                    System.out.print("''");
                }
                counter++;
            }
            else
            {
                System.out.print(charInput[i]);
            } 
        }
        System.out.print("\n");
    }

The program supposed to stopped when it's already reached the EOF, but I don't know why, for some reasons it keeps running and result a runtime error. Please help. By the way I'm new here, sorry if my question is not really clear to be understood, Thank you before :)

回答1:

It keeps running because it hasn't encountered EOF. At end of stream:

1. read() returns -1.
2. read(byte[]) returns -1.
3. read(byte[], int, int) returns -1.
4. readLine() returns null.
5. readXXX() for any other X throws EOFException.
6. Scanner.hasNextLine() returns false.
7. Scanner.nextLine() throws NoSuchElementException.

Unless you've encountered one of these, your program hasn't encountered end of stream. NB \u001a is a Ctrl/z. Not EOF. EOF is not a character value.

回答2:

This is what I did

Scanner s = new Scanner(f); //f is the file object

while(s.hasNext())
{
String ss = s.nextLine();
System.out.println(ss);
}

Worked for me

回答3:

You can use try and catch.

Scanner n=new Scanner(System.in);
String input;
int counter=0;
input=n.nextLine();
try{
    while(input!=null)
    { 
        char[] charInput=input.toCharArray();
        for (int i = 0; i < input.length(); i++) {
            if(charInput[i]=='"')
            {
                if(counter%2==0)
                {
                    System.out.print("``");
                }
                else
                {
                    System.out.print("''");
                }
                counter++;
            }
            else
            {
                System.out.print(charInput[i]);
            } 
        }
        System.out.print("\n");
        input=n.nextLine();
    }
}catch(Exception e){

}

Here, when you will give Ctrl+z, Scanner.nextLine() will give you NoSuchElementException. Use this exception as a condition of EOF. To handle this exception use try and catch.

来源：https://stackoverflow.com/questions/36515937/how-to-detect-eof-in-java