如何分别使用 for 循环隐藏字符？

Question

I want to basically hide characters following three constant dots (...), the pattern goes like this:

---

Inputs a phrase from the user and outputs the phrase followed by three dots (...), then the phrase minus one character followed by three dots (...), then the phrase minus two characters followed by the dots, and so on until only one dot is left.

Note: This has to be done using nested for loops only

Sample input

 1
 disappear

Expected output:

 disappear...
 disappea...
 disappe...
 disapp...
 disap...
 disa...
 dis...
 di...
 d...
 ...
 ..
 .

This is my attempt:

Problem : I am unable to make it so the phrase decreases each time (minus 1 each time)

I tried using the charAt(); method, but it wouldn't work, I am sure that you would need a for loop separate for each of the dots or a whole set of dots, in this case.

import java.util.Scanner;
public class Dissappear{
public static void main(String[]args){
    Scanner keyboard = new Scanner(System.in);
    int option = keyboard.nextInt();
    String phrase = keyboard.next();
        if (option == 1){
            for (int x = 0; x <= phrase.length(); x++){
                    System.out.print(phrase + "...");
                for (int y = 0; y <= phrase.length(); y++){
                    char n = phrase.charAt(y);
                    System.out.print(n+"...");
                }
            }
        }
     }
 }

Answer 1

This is how I got it to work:

public class Disappear {
    public static void main(String... args) {
        String word = "disappear";
        int originalLength = word.length();

        for(int i = 0; i < originalLength; i++) {
            System.out.println(word.substring(0, originalLength - i) + "...");
        }

        for(int i = 0; i < 3; i++) {
            for(int j = 0; j < 3 - i; j++) {
                System.out.print(".");
            }
            System.out.println();
        }
    }
}

Without substring:

public class Disappear {
    public static void main(String... args) {
        String word = "disappear";
        int originalLength = word.length();

        for(int i = 0; i < originalLength; i++) {
            for(int j = 0; j < originalLength - i; j++) {
                System.out.print(word.charAt(j));
            }

            System.out.println("...");
        }

        for(int i = 0; i < 3; i++) {
            for(int j = 0; j < 3 - i; j++) {
                System.out.print(".");
            }
            System.out.println();
        }
    }
}

Answer 2

You can do it with StringBuilder:

    StringBuilder stringBuilder = new StringBuilder(str);

    System.out.println(str + "...");
    for (int i = 0; i < length; i++) {
        stringBuilder.deleteCharAt(stringBuilder.length() - 1);
        System.out.println(stringBuilder.toString() + "...");
        if (i == length - 1) {
            for (int j = 0; j < 2; j++) {
                for (int k = j; k < 2; k++) {
                    System.out.print(".");
                }
                System.out.println();
            }
        }

Answer 3

Ok! Nested for loops. But the outer one is only included to meet the requirement. Probably not in the spirit of the assignment though. Just keep decrementing k until it is zero and then latch it there until the StringBuilder length is 0 and the inner loop terminates.

StringBuilder sb = new StringBuilder("disappear...");
for (;;) {
    for (int k = sb.length() - 4; sb.length() > 0;) {
        System.out.println(sb);
        sb.delete(k, k + 1);
        k = k > 0 ? --k : 0;
    }
    break;
}