问题和练习

• 问题
• 练习题

问题

1. 以下字符串生成器的初始容量是多少？

   StringBuilder sb = new StringBuilder("Able was I ere I saw Elba.");
   

   答：初始字符串为 24 + 默认容量大小 16 = 42

2. 考虑下面的字符串:

   String hannah = "Did Hannah see bees? Hannah did.";
   

   1. 表达式 hannah.length() 是多少

      答：32

   2. 方法调用 hannah.chatAt(12) 返回的值是多少

      答：e

   3. 写一个表达式来引用 hannah 中的 b 字母

      答：hannah.charAt(15)

3. 由以下表达式返回的字符串有多长？字符串是什么？

   "Was it a car or a cat I saw?".substring(9, 12)
   

   答：3，char，不包含 12 所在索引的字符

4. 在下面的程序中 ComputeResult， 每个编号行执行后的 result 值是多少？

       public class ComputeResult {
       public static void main(String[] args) {
           String original = "software";
           StringBuilder result = new StringBuilder("hi");
           int index = original.indexOf('a');
   
   /*1*/   result.setCharAt(0, original.charAt(0));
   /*2*/   result.setCharAt(1, original.charAt(original.length()-1));
   /*3*/   result.insert(1, original.charAt(4));
   /*4*/   result.append(original.substring(1,4));
   /*5*/   result.insert(3, (original.substring(index, index+2) + " "));
   
           System.out.println(result);
       }
   }
   

   答：

   1. si
   2. se
   3. swe
   4. sweoft
   5. swear oft

练习题

1. 写出两种获取 "Hi, mom." 字符串的方法：

   String hi = "Hi, ";
   String mom = "mom.";
   

   答： hi.concat(mom) 和 hi + mom.

2. 写一个程序，把你全名的单词首字母打印出来

   public class ComputeInitials {
       public static void main(String[] args) {
           String myName = "Fred F. Flintstone";
           StringBuffer myInitials = new StringBuffer();
           int length = myName.length();
   
           for (int i = 0; i < length; i++) {
               if (Character.isUpperCase(myName.charAt(i))) {
                   myInitials.append(myName.charAt(i));
               }
           }
           System.out.println("My initials are: " + myInitials);
       }
   }
   

3. 给定两个字符串，只保留字母并且全部转换成小写，然后按照自然顺序排列后再比较两个字符串是否相同

   public class Anagram {
   
       public static boolean areAnagrams(String string1,
                                         String string2) {
   
           // 只保留字母
           String workingCopy1 = removeJunk(string1);
           String workingCopy2 = removeJunk(string2);
   
           // 全部转换成小写
           workingCopy1 = workingCopy1.toLowerCase();
           workingCopy2 = workingCopy2.toLowerCase();
   
           // 排序
           workingCopy1 = sort(workingCopy1);
           workingCopy2 = sort(workingCopy2);
   
   
           return workingCopy1.equals(workingCopy2);
       }
       // 只保留字母
       protected static String removeJunk(String string) {
           int i, len = string.length();
           StringBuilder dest = new StringBuilder(len);
           char c;
   
           for (i = (len - 1); i >= 0; i--) {
               c = string.charAt(i);
               // 确定指定字符是否为字母。
               if (Character.isLetter(c)) {
                   dest.append(c);
               }
           }
   
           return dest.toString();
       }
   
       protected static String sort(String string) {
           char[] charArray = string.toCharArray();
   
           java.util.Arrays.sort(charArray);
   
           return new String(charArray);
       }
   
       public static void main(String[] args) {
           String string1 = "Cosmo and Laine:";
           String string2 = "Maid, clean soon!";
   
           System.out.println();
           System.out.println("Testing whether the following "
                                      + "strings are anagrams:");
           System.out.println("    String 1: " + string1);
           System.out.println("    String 2: " + string2);
           System.out.println();
   
           if (areAnagrams(string1, string2)) {
               System.out.println("They ARE anagrams!");
           } else {
               System.out.println("They are NOT anagrams!");
           }
           System.out.println();
       }
   }