public static String removeDuplicate(String s)
{
    char [] temp = s.toCharArray();
    int length =temp.length;
    for (int i=0;i<length;i++)
    {
        for (int j = i+1; j<length;j++)
        {
            if(temp[i]==temp[j])
            {
                int test =j;
                for(int k=j+1; k<length ; k++)
                {
                    temp[test] = temp[k];
                    test++;
                }
                length--;
                j--;
            }
        }
    }
    return String.copyValueOf(temp).substring(0,length);
}

public static String removeDuplicates(String str) {
    int charsCount[] = new int[256];

    for (int i = 0; i < str.length(); i++) {
        char ch = str.charAt(i);
        charsCount[ch]++;
    }

    StringBuilder sb = new StringBuilder(charsCount.length);
    for (int i = 0; i < charsCount.length; i++) {
        if (charsCount[i] > 0) {
            sb.append((char)i);
        }
    }

    return sb.toString();
}

public static String removeDuplicates(String str) {
    boolean seen[] = new boolean[256];
    StringBuilder sb = new StringBuilder(seen.length);

    for (int i = 0; i < str.length(); i++) {
        char ch = str.charAt(i);
        if (!seen[ch]) {
            seen[ch] = true;
            sb.append(ch);
        }
    }

    return sb.toString();
}

import java.util.Set;
import java.util.HashSet;

public static String removeDuplicate(String s)
{
    StringBuilder sb = new StringBuilder();
    Set<Character> seen = new HashSet<Character>();

    for(int i = 0; i < s.length(); ++i) {
        char c = s.charAt(i);
        if(!seen.contains(c)) {
            seen.add(c);
            sb.append(c);
        }
    }
    return sb.toString();
}

public static String removeDuplicate(String s) {
    char[] temp = s.toCharArray();
    int length = temp.length;
    for (int i = 0; i < length; i++) {
        for (int j = i + 1; j < length; j++) {
            if (temp[i] == temp[j]) {
                int test = j;
                for (int k = j + 1; k < length; k++) {
                    temp[test] = temp[k];
                    test++;
                }
                length--;
                j--;
            }
        }
    }
    return String.copyValueOf(temp).substring(0, length);
}

private static final boolean foundIn(char[] temp, int size, char c) {
    for (int i = 0; i < size; i++) {
        if (temp[i] == c) {
            return true;
        }
    }
    return false;
}

public static String removeDuplicateY(String s) {
    char[] temp = s.toCharArray();
    int size = 0; //how many unique chars found so far
    for (int i = 0; i < temp.length; i++) {
        if (!foundIn(temp, size, temp[i])) {
            // move the first-time char to the end of the return value
            temp[size] = temp[i];
            size++;
        }
    }
    return new String(temp, 0, size);
}

public static String removeDuplicates(String str){
    int checker=0;
    int val=0;
    String out="";
    for(int i =0;i<str.length();i++){
        val = str.charAt(i)-97;
        if((checker & 1<<val) ==0) out +=str.charAt(i)+"";
        checker|=(1<<val);
    }
    return out;
}