Java-String類的常用方法

1. 提取子串

   //s.substring(begin, end);
   //截取 從begin -- end-1 區間內的字符
   String s1 = new String("0123456789");
   String s2 = s1.substring(2, 7);
   System.out.println(s2);

2. 字符串比較

   String str1 = new String("abc");
   String str2 = new String("ABC");
   int a = str1.compareTo(str2);// a > 0
   int b = str1.compareToIgnoreCase(str2);// b = 0
   boolean c = str1.equals(str2);// c = false
   boolean d = str1.equalsIgnoreCase(str2);// d = true

        

3. 字符串查找

   //s.idexOf(char a/String str) 用於查找當前字符串中字符或子串，返回字符或子串在當前字符串中從左邊起首次出現的位置，若沒有出現則返回-1。//s.idexOf(char a/String str, int pos) 從pos 位置往右查找 字符a
   //s.lastIndexOf(char a/String str) 從右往左查找
   //s.lastIndexOf(char a/String str， int pos) 從pos 位置看i是往左查找
   String str = "I am a good student";
   int a = str.indexOf('a');//a = 2
   int b = str.indexOf("good");//b = 7
   int b1 = str.indexOf("goood");//b1 = -1
   int c = str.indexOf("g",2);//c = 7
   int d = str.lastIndexOf("a");//d = 5
   int e = str.lastIndexOf("am",5);//e = 2

    

4. 字符串中字符的大小寫轉換

   String s = new String("Hello World");
   String s1 = s.toLowerCase();//hello world
   String s2 = s.toUpperCase();//HELLO WORLD

    

5. 字符串中字符的替換

   String str = "asdzxcasd";
   String str1 = str.replace('a','g');//str1 = "gsdzxcgsd"
   String str2 = str.replace("asd","fgh");//str2 = "fghzxcfgh"
   String str3 = str.replaceFirst("asd","fgh");//str3 = "fghzxcasd"
   String str4 = str.replaceAll("asd","fgh");//str4 = "fghzxcfgh"
       

    

6. 判斷是否存在某個子串

   String str = "123123123123123";
   String s = "12";
   boolean flag = str.contains(s);// flag = true