String和StringBuilder

. 1  Import java.util.Collections;
 2  
. 3  Import  static com.sun.org.apache.xml.internal.security.keys.keyresolver.KeyResolver.length;
 . 4  // Java string does not change unless the re-assignment 
. 5  public  class string {
 . 6      public  static  void main (string [] args) {
 . 7          string STR = "44 is" ;
 . 8          int NUM = the Integer.parseInt (STR);
 . 9          STR = String.valueOf (NUM);
 10  
. 11          STR = "DFA , SDF, ADSF, asd, the FASD, Fas, df " ;
 12         String[] strings = str.split(",");
13         str = String.join(",", strings);
14 
15         //左闭右开区间
16         String string = str.substring(3,6);
17 
18         char c = string.charAt(1);
19         int d = string.compareTo(string);
20         String  ss = string.concat(string);
21         boolean b = ss.contains("a");
22         b = ss.startsWith("s");
23         b = ss.endsWith("s");
24         b = ss.isEmpty();
25 
26         b = ss.matches("a");
27 
28         ss = ss.replaceAll("sf" ,"asdf");
29         ss = ss.replaceFirst("sf" ,"asdf");
30 
31         char[] chars = ss.toCharArray();
32 
33         ss = ss.toLowerCase();
34         ss = ss.toUpperCase();
35         ss = ss.trim();
36 
37         //StringBuilder
38 
39         StringBuilder stringBuilder = new StringBuilder("");
40         stringBuilder.append("sdf");
41         int aa = stringBuilder.capacity();
42         int bb = stringBuilder.length();
43 
44         stringBuilder.delete(1, 2);//左闭右开
45 
46         stringBuilder.reverse();
47         stringBuilder.deleteCharAt(1);
48         stringBuilder.insert(0, "0000");
49 
50     }
51 }