Java Program to check if String has all unique characters

Using HashSet

import java.util.*;

public class Main {
    public static void main(String[] args) {
        System.out.println("Apple has all unique chars : " + hasAllUniqueChars("apple"));
        System.out.println("index has all unique chars : " + hasAllUniqueChars("index"));
        System.out.println("world has all unique chars : " + hasAllUniqueChars("world"));
    }

    private static boolean hasAllUniqueChars(String word) {
        Set<Character> set = new HashSet<>();
        for (int index = 0; index < word.length(); index++) {
            char ch = word.charAt(index);
            // If Hashset's add method return false,
            // that means it is already present in HashSet
            if (!set.add(ch))
                return false;
        }
        return true;
    }
}

Using ASCII value of character

1. Create a boolean array of 26 length

2. Convert char to uppercase and get its ASCII value

3. Subtract 64 to the ASCII value to get an index between 0 to 25.

4. If a character is not repeated then we should have false in the boolean array

public class Main {
    public static void main(String[] args) {
        System.out.println("Apple has all unique chars : " + hasAllUniqueChars("apple"));
        System.out.println("index has all unique chars : " + hasAllUniqueChars("index"));
        System.out.println("world has all unique chars : " + hasAllUniqueChars("world"));
    }

    private static boolean hasAllUniqueChars(String word) {
        boolean[] charMap = new boolean[26];
        word = word.toUpperCase();

        for (int index = 0; index < word.length(); index++) {
            // we are subtracting char's ascii value to 64, 
            // so we get all index from 0 to 25.
            int asciiCode = (int) word.charAt(index) - 64;

            // If char is not present, it should have false at that index
            if (!charMap[asciiCode])
                charMap[asciiCode] = true;
            else
                return false;
        }

        return true;
    }
}