remove duplicate characters from a string in java without using string function

You could create a Scanner which reads that string as if you where reading it through a stream.

    String input = "Hello World";
    Scanner scanner = new Scanner(input);
    scanner.useDelimiter("");
    while(scanner.hasNext()) {
        System.out.println(scanner.next());
    }

Yields:

H
e
l
l
o

W
o
r
l
d

All the other answers are bypassing the use of String methods by using other classes, such as StringBuilder or Scanner. However, they are still using String methods, albeit indirectly, because these other classes themselves use String methods. My solution is a bit "naughty" and jdk-specific, but at least it doesn't use any String methods at all:

    String s = "hello";
    Class<String> c = (Class<String>) Class.forName("java.lang.String");
    Field f = c.getDeclaredField("value");
    f.setAccessible(true);
    char[] array = (char[]) f.get(s);

... and then do your processing entirely on the array.

See, no String methods used! ;-)

charAt and length are from Interface CharSequence

So go with the StringBuilder and use the it's implementation of those too methods.

StringBuilder sb = new StringBuilder("My My My");

And using

sb.length()

in combination with

sb.chartAt(index);

you can iterate over your stringbuilder identify the duplicates, and remove them using

sb.deleteCharAt(index_of_char_to_delete);

How about this?

    String str = "eyyigwdqweqe";
    StringBuilder builder = new StringBuilder(str);
    HashSet<String> mySet = new HashSet<String>();

    for(int i = 0; i<builder.length();i++)
        mySet.add(builder.charAt(i)+"");
    System.out.println(mySet);

public class RemoveDuplicates {

    public static void main(String[] args) {

        String input = new String("Geeksforgeeks");
        String output = new String();
        boolean isPresent;

        if (input.length()==0){
            System.out.println("Input String Empty. Program Terminated");
        }
        else {
            //read each character of input string 
            for (int i = 0; i < input.length(); i++) {
                isPresent=false;

                //read through entire output string 
                for (int j = 0; j < output.length(); j++) {

                    //check if character exists in output string then set flag
                    if (Character.toLowerCase(input.charAt(i)) == Character.toLowerCase(output.charAt(j))) {
                        isPresent = true;
                        break;
                    }
                }//for              
                //if flag is false means character is not dduplicated then add to output string
                if (!isPresent) {
                    output += input.charAt(i);
                }//if               
        }//end of input string loop         
        System.out.println("Original input : "+input);
        System.out.println("Final output   : "+output);
        }
    }//main
}//class

You can use slice() function to remove the character from the left of the string.

var string= 'testautomation';

var stringfinal=string.slice(4);

cy.log(stringfinal)

Output: automation