Removing duplicated chararters in char[]

Ch1.java

package org.sooo;

public class Ch1 {
    public static char[] removeDup(char[] str) {
        if (str == null || str.length == 1) {
            return str;
        }

        // mark duplicated characters to special character (a.k.a. dupChar).
        char dupChar = '\0';
        int dupCount = 0, i = 0;
        while (i < str.length) {
            if (str[i] == dupChar) {
                i++;
                continue;
            }

            for (int j=i+1;j<str.length;j++) {
                if (str[i] == str[j]) {
                    str[j] = dupChar;
                    dupCount++;
                }
            }
            i++;
        }

        // make a new array except dupChar.
        char[] result = new char[str.length - dupCount];
        i = 0;
        for(char c : str) {
            if (c != dupChar) {
                result[i] = c;
                i++;
            }
        }

        return result;
    }

    static void print(char[] str) {
        if (str == null) {
            System.out.println("null");
            return;
        }

        for (char c : str) {
            System.out.print(c);
        }
        System.out.println();
    }

    public static void main(String[] args) {
        print(Ch1.removeDup(null));
        print(Ch1.removeDup(new char[]{'a'}));
        print(Ch1.removeDup(new char[]{'a', 'b'}));
        print(Ch1.removeDup(new char[]{'a', 'b', 'a'}));
        print(Ch1.removeDup(new char[]{'a', 'b', 'c', 'b', 'a'}));
        print(Ch1.removeDup(new char[]{'a', 'a', 'a', 'a', 'a'}));
    }
}