课本5.9

 1            String str3 = new String("JhdhdFdeGDEmK");
 2            String str1 = str3.toUpperCase();
 3            String str2 = str3.toLowerCase();
 4            System.out.println(str1 + "\n" + str2);
 5            
 6            System.out.println();
 7            
 8            String a1 = str1.substring(2, 3);
 9            String a2 = str2.substring(3, 4);
10            if(a1.equalsIgnoreCase(a2) == true)
11            {
12                System.out.println("两个字串相同");
13            }
14            else
15            {
16                System.out.println("两个字串并不相同");
17            }
18            
19            System.out.println();
20            
21            StringBuilder str = new StringBuilder("fgjk");
22            int i = 1;
23            while(i <= 10)
24            {
25                str.append(i);
26                i++;
27            }
28            System.out.println(str);