当我尝试添加更多代码时，为什么编译器会抱怨“虽然期望”？

Question

Write a program with a word containing @ character as an input. If the word doesn't contain @, it should prompt the user for a word with @. Once a word with @ is read, it should output the word then terminate.

This is what I have done so far:

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

        System.out.println(" Please enter a word with @ ");
        Scanner scan = new Scanner(System.in);

        String bad = "@";

        String word = scan.next();
        do
            if (!word.contains(bad))
                System.out.println(" Please try again ");
            else
                System.out.println(" " + word);
        while (!word.contains(bad));
    }
}

I can get it to terminate after a word containing "@" is given as input, but if I try to add a Scanner to the line after "please try again", it says while expected .

Answer 1

I think issue is you are missing surrounding braces for do/while:

       do
          if (!word.contains( bad ))
            System.out.println( " Please try again " );

            else 
            System.out.println( " " + word);

        while ( !word.contains( bad ));

should be:

do
{
            if (!word.contains( bad ))
            System.out.println( " Please try again " );

            else 
            System.out.println( " " + word);
}while ( !word.contains( bad ));

Some people may not like this, but my suggestion is always use open/close braces. In this case, for the code if/else also. It avoids lot of confusion.

Answer 2

This is where your problem lies:

       do
            if (!word.contains(bad))
                System.out.println(" Please try again ");
            else
                System.out.println(" " + word);
        while (!word.contains(bad));

You need to put braces from where the loop starts until it ends. |So this thing should like:

do {
    if (!word.contains(bad))
        System.out.println(" Please try again ");
    else
        System.out.println(" " + word);
} while(!word.contains(bad));

For Better Practice You should Check do...while loops here .

Answer 3

There are two issues.

1. Your code is not using the braces properly
2. you are not attempting to read the new word if right word is not entered.

Also I prefer while loop better in the case as opposed to do-while loop as below.

    Scanner scan = new Scanner ( System.in );
    String required= "@";
    System.out.println( " Please enter a word with @ " );
    String word = scan.next() ;

    //check if the right word(containing @) is entered, 
    //if not then loop until it is enteres
    while((!word.contains(required)){
        System.out.println( " Please try again " );
        //read the new word as input from the user
        word = scan.next() ;
    }
    //right word is entered, display it
    System.out.println(word);

Also please note that when you use scan.next() , it reads each word separately if entered in the same line.

Answer 4

The problem with your code is it is not re-reading the word in your loop. Modify your loop like this (minimum change to your code).

do {
        word = scan.next();
        if (!word.contains(bad))
            System.out.println(" Please try again ");

        else
            System.out.println(" " + word);
    }
    while (!word.contains(bad));

And yes as others have pointed out try to use braces especially with nested constructs.