String类

1. String类型访问里面的每一个字符可以使用s.charAt(i)

   String s = "hello";  //s.charAt(0) = h

---

2. 产生随机数

   double b = Math.random();   //产生[0,1)之间的小数
   int n = (int)(b * 5);       //产生[0,5)之间的整数
   int m = 1 + (int)(b * 6);   //产生[1,6]之间的整数

---

3. public boolean equals(String s),比较当前String对象字符序列和参数的字符序列是否相等
   equalsIgnoreCase()方法在比较时会忽略大小写

   String Tom = new String("木头人");
   String Marry = new String("植物人"); 
   String Jack = new String("植物人"");
   System.out.println(Tom.equals(Marry));  //结果为false
   System.out.println(Jack.equals(Marry)); //结果为true 
   System.out.println(Jack == Marry);      //结果为false

由于string对象Marry和Jack存放的是引用,其所在的内存不一样,因而内容相同却不相等

---

4. public boolean startsWith(String s)/endsWith(String s)
   s1.startsWith(s2) :判断当前String对象的字符序列前缀是否和参数相同
   s1.endsWith(s2) :判断当前String对象的字符序列后缀是否和参数相同

---

5. public int compareTo(String s)
   s1.compareTo(s2)  :按照字典序比较s1和s2的字符序列是否相同,相同返回0,s1 > s2返回正值, s1 < s2返回负值

---

6. public boolean contains(String s)
   s1.contains(s2):判断s1中是否包含s2

   String Tom = "students";
   System.out.println(Tom.contains("stu")); //值为ture
   System.out.println(Tom.contains("ab")); //值为false

---

7. public int indexOf(String s) / lastIndexOf(String s)
   s1.indexOf(s2):从s1中的0位置开始搜索s2,并返回首次出现s2的位置,如果没有找到就返回-1,lastIndexOf()则是从末尾开始搜索
   indexOf(String str, int startpoint)重载方法,startpoint指定检索的开始位置

   String tom = "I am a good cat";
   tom.indexOf("a");       //值为2
   tom.indexOf("good", 2);  //值为7
   tom.indexOf("a", 7);     //值为13
   tom.indexOf("w", 2);     //值为-1

---

8. public String substring(int startpoint)
   s2 = s1.substring(start); //从start位置开始复制s1中字符串到s2中
   s2 = s1.substring(start, end) //从start位置开始截至end-1复制s1中字符串到s2中

   String s = "abcdefg";
   String s1 = s.substring(0);  //s1 = "abcdefg";
   String s2 = s.substring(2, 4);  //s2 = "cd";

---

9. public String trim()
   去掉字符序列中的前后空格

   String s = " abcd ";
   System.out.println(s.trim());  //结果为abcd

---

10. public void getChars(int start, int end, char c[], int offset)
    将String对象从start到end-1的字符存放到从offset位置开始的c数组中

    String s = "abcdefg";
    char c[] = new char[10];
    s.getChars(0, 2, c, 0);
    System.out.println(c);   //输出结果为ab

---

11. public char[] toCharArray()
    将String中的字符序列全部存放在数组中

    String s = "abcdefghijk";
    char c[] = s.toCharArray();
    System.out.println(c);      //输出结果为abcdefghijk

---

12. public boolean matches(String regex)
    判断当前字符串是否匹配给定的正则表达式, 是返回true, 否则返回false

    String s = "[1234]?";
    String s1 = "123";
    System.out.println(s1.matches(s1));

---

13. public String repalceAll(String regex, String replacement)
    匹配当前对象中字符序列和regex中相同的, 用replacement全部替换

    String s = "hello";
    String s1 = "hello world";
    System.out.println(s1.replacement(s, "welcome to my")); //结果为welcome to my world

---