Replacement of the symbol on another

[Cleofas]

Replace all the symbols of position (3) with the symbol of position 0. Don't tell me how to do it. It's from index 0 to index 3, I only know by replace

[meriah]

Try the following code:

        public static void main(String[] args) {
            String exampleStr = "Hello, World!";
            // Замена всех символов с 0 позиции ('H') на символ с 3 позиции ('l')
            System.out.println(replaceAllByIndex(exampleStr, 0, 3));
            // Замена всех символов с 4 позиции ('o') на символ с 12 позиции ('!')
            System.out.println(replaceAllByIndex(exampleStr, 4, 12));
        }
    public static String replaceAllByIndex(String input, int dstIdx, int srcIdx) {
        return input.replace(input.charAt(dstIdx), input.charAt(srcIdx));
    }

It's a function. replaceAllByIndex performs the replacement of all symbols on the index dstIdx with index symbol srcIdx in line input♪

However, if your purpose is simply to change the places of two symbols (not all driving), use the following function instead. replaceAllByIndex in code above:

        public static String swapChars(String input, int lIdx, int rIdx) {

StringBuilder sb = new StringBuilder(input);

sb.setCharAt(lIdx, input.charAt(rIdx));

sb.setCharAt(rIdx, input.charAt(lIdx));

return sb.toString();

}

Programme findings in the first and second cases, respectively: