列举出给定数量的字符的所有组成情况-java实现

 1  　　public static String itr;
 2 
 3     public static void main(String[] args) {
 4         String s = "abcd";
 5         printGroup(s);
 6     }
 7 
 8     public static void printGroup(String in){
 9         itr = in;
10         for (int i = 0; i < itr.length() ; i++) {
11             String c = itr.charAt(i)+"";
12             String low = itr.substring(0,i)+itr.substring(i+1);
13             print(c,low);
14             System.out.println();
15         }
16     }
17     public static String cutStr(String cut){
18         char[] sa = itr.toCharArray();
19         char[] ca = cut.toCharArray();
20         int k = sa.length-ca.length;
21         char[] str = new char[k];
22         int i = 0;
23         A:for (char s : sa) {
24             for (char c : ca) {
25                 if(s==c){
26                     continue A;
27                 }
28             }
29             str[i++] = s;
30             if(i==k){
31                 break ;
32             }
33         }
34         return new String(str);
35     }
36 
37     private static void print(String c,String str){
38         for (int i = 0; i < str.length(); i++) {
39             String s = c + str.charAt(i);
40             System.out.print(s+" ");
41             print(s,cutStr(s));
42         }
43     }

ab abc abcd abd abdc ac acb acbd acd acdb ad adb adbc adc adcb 
ba bac bacd bad badc bc bca bcad bcd bcda bd bda bdac bdc bdca 
ca cab cabd cad cadb cb cba cbad cbd cbda cd cda cdab cdb cdba 
da dab dabc dac dacb db dba dbac dbc dbca dc dca dcab dcb dcba