去重五种方法

public class Quchong {
    public void quchong(){
//set集合
        Scanner s = new Scanner(System.in);
        System.out.println("请输入一个字符串");
        String a = s.next();
        Set set = new HashSet();
        for (int i = 0; i < a.length(); i++) {
            char b = a.charAt(i);
            set.add(b);
        }
        String ss = "";
        for (Object o : set) {
            ss += o;
        }
        System.out.println(ss);
    }
    public void quchong2(){
//list集合
        Scanner s = new Scanner(System.in);
        System.out.println("请输入一个字符串");
        String a = s.next();
        List list = new ArrayList();
        String result = "";
        for (int i = 0; i < a.length(); i++) {
            String ss = a.charAt(i)+"";
            if(!list.contains(ss)){
                list.add(ss);
            }
        }
        for (Object o : list) {
            result += o;
        }
        System.out.println(result);
        
    }
    public void quchong3(){
//原生字符串
        Scanner s = new Scanner(System.in);
        System.out.println("请输入一个字符串");
        String a = s.next();
        String result = "";
        for (int i = 0; i < a.length(); i++) {
            String ss = a.charAt(i)+"";
            if(result.indexOf(ss) == -1){
                result = result + ss;
            }
        }
        System.out.println(result);
    }
    public void quchong4(){
//HashMap
        Scanner s = new Scanner(System.in);
        System.out.println("请输入一个字符串");
        String a = s.next();
        Map map = new HashMap();
        String result = "";
        for (int i = 0; i < a.length(); i++) {
            String ss = a.charAt(i)+"";
            map.put(ss,"1");
        }
        Set aa = map.keySet();
        for (Object o : aa) {
            result += o;
        }
        System.out.println(result);
    }
    public void quchong5(){
//字符串数组
        Scanner s = new Scanner(System.in);
        System.out.println("请输入一个字符串");
        String a = s.next();
        String result = "";
        String[] arr =a.split("");
        for (int i = 0; i < arr.length; i++) {
            if(result.indexOf(arr[i]) == -1){
                result += arr[i];
            }
        }
        
        System.out.println(result);
    }
}