如何在不使用集合的情况下从数组中删除未使用的元素

Question

I had an array of elements that I have converted in a String. But this String keeps again the empty elements of the array and I can't compare it with another String.

How can I delete the empty elements on it? I don't know how to use the Collections, is there another way?

char[] copyLoop = new char[26];
        for (int i = 0; i < letters.length; i++) {
            if (letters[i] > 1) {
                char c = (char) (i + 97);
                copyLoop[i] = c;       
            }
        }
        String rslt = String.copyValueOf(copyLoop);
        return rslt;

Answer 1

There are no "empty" elements in an array, and you can't resize arrays either. All you can do is to put all of the elements you're interested in at one end of the array (eg starting at zero) with no "uninteresting" elements between them, and then construct a string from a portion of the array.

Use another variable to store the index of the next "empty" element in the array: every time you find a letter, increment this variable. Once you've finished iterating letters , this variable will contain the length of the array to use to create the string.

    char[] copyLoop = new char[26];
    int dst = 0;
    for (int i = 0; i < letters.length; i++) {
        if (letters[i] > 1) {
            char c = (char) (i + 97);
            copyLoop[dst++] = c;       
        }
    }
    return new String(copyLoop, 0, dst);

Or, of course, use a StringBuilder (which is doing effectively the same internally):

    StringBuilder copyLoop = new StringBuilder(26);
    for (int i = 0; i < letters.length; i++) {
        if (letters[i] > 1) {
            char c = (char) (i + 97);
            copyLoop.append(c);       
        }
    }
    return copyLoop.toString();

Answer 2

Unfortunately not. Arrays in Java are not shrinkable/expandable, their size is set constant. There are two ways you can work around:

1. Use Collections, ie create a List of Characters ArrayList<Character> list = new ArrayList<>(); , use it and delete items you don't need after each loop cycle.

2. On every cycle of your for loop, when you need to delete an item inside your Array, just create a new char[] array, which is smaller and copy the contents of the old one to the new, except for the value you deleted.

Also, if you are working with Strings, it's recommended to use mutable String classes sa StringBuilder or StringBuffer which let you add/remove characters from the String. In your case that seems to be the best solution.