如何在Java中使用For循环重复字符串的字符

Question

I'm trying to figure out how to take a word as input from a user, then return that same string in a different format.

For example, the input "dog" needs to show up as

d
oo
ggg

I can only use for-statements, not if-statements...and the program is supposed to only have 2 methods, the second one should return a value.

I know how to take the input from the user, but I'm a bit lost on how to return a string that's formatted like the one above.

This IS a homework question, so I'm not expecting anyone to just give me the answer. I'm really just stuck and have no idea what to do next. It's a basic java 1 class, so I can't use anything too complicated.

Here's my unfinished code so far. I know it has a ton of problems >.<

    import java.util.Scanner;

    public class Lab06Edit {

       public static void main(String[] args ) {
          Scanner keyboard = new Scanner(System.in);
          System.out.print("Enter a word:  ");
          String input = keyboard.next();

       wordAngle(input);
       System.out.print("" + wordAngle(input));

    }

       public static String wordAngle(String word) {
          String result = "";
          for (int i=0; i<=input.length(); i++) {
             System.out.println(input.charAt(i)*i +"\n");
          return result;
          }     
       }
    }

Answer 1

If you multiply char with integer than char will be converted to ASCII code and result will be integer . You should concat char with String to produce your desired result. Look at your expected output code in below:

 public class Lab06Edit {

    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Enter a word:  ");
        String input = keyboard.next();
        wordAngle(input);
    }

    public static void wordAngle(String input) {
        for (int i = 0; i < input.length(); i++) {
            String result = "";
            for (int j = 0; j <= i; j++) {
                result += input.charAt(i);
            }
            System.out.println(result);
        }
    }
}

Answer 2

Printing a letter multiple times

input.charAt(i)*i is a little surprising at first but you are trying to multiple a letter. Unsurprisingly java doesn't like this and converts the letter to a number before multiplying it. Hence (after removing a few bugs) an input of dog gives an output of. To an extent this is Java's fault as string + string works.

0      % d=100, 0*100=0

111    % 0=111 1*111=111

206    % g=103 2*103=206

If you want to print something multiple times, then the easiest way (not necessarily the best way, but this is homework after all) is to put it in a for loop, you can use System.out.print rather than System.out .println to avoid advancing the line. In your case a for loop within a for loop. Alternatively you can build a string piece by piece and + them together in a loop (still not best but better) and return that string to be printed within a println statement. Give it a go and see if you can figure it out, ask if you need more of a hint.

Array length

for (int i=0; i<=input.length(); i++) remember everything is zero based in java, so if something has length 3 it has elements 0,1,2. You current code has 0,1,2,3. When your code gets to the mythical element 3 it returns a String index out of range exception.

Minor mistakes

You've put the return statement inside the for loop, I presume a mistake, and you've also changed from using variable name word to input, again I assume a typo