String類的三個內建正則表達式工具：

1.matches()方法

示例：檢查一個句子是否以大寫字母開頭，以句號結尾　

1     public static boolean checkFormat(String sentence){
2         return sentence.matches("^[A-Z].+\\.$");
3     }

2.split()方法

示例：以空格分割knights字元串並以數組形式返回

1     public static void test(){
2         String knights = 
3                 "Then, when you have found the shrubbery,"
4                 + "you must cut down the mightiest tree in the forest... "
5                 + "with... a herring";
6         String newString = Arrays.toString(knights.split(" "));
7         System.out.println(newString);
8     }

3.replaceFirst()和replaceAll()方法

示例：替換knights字元串中所有母音字母為下劃線

1     public static void test(){
2         String knights = 
3                 "Then, when you have found the shrubbery,"
4                 + "you must cut down the mightiest tree in the forest... "
5                 + "with... a herring";
6         String newKnights = knights.replaceAll("[AaEeIiOoUu]", "_");
7         System.out.println(newKnights);
8     }

replaceFirst()方法只在首次出現時替換，replaceAll則替換所有滿足條件的部分