Common methods in String

1. length(): Returns the length of the string.

   String str = "Hello";
   int length = str.length();  // length的值为5
   

2. charAt(int index): Returns the character at the specified index position in the string.

   String str = "Hello";
   char ch = str.charAt(1);  // ch的值为'e'
   

3. substring(int beginIndex) and substring(int beginIndex, int endIndex): Returns the substring from the specified index to the end.

   String str = "Hello World";
   String substr1 = str.substring(6);  // substr1的值为"World"
   String substr2 = str.substring(0, 5);  // substr2的值为"Hello"
   

4. equals(Object obj): compares whether the string is equal to the specified object.

   String str1 = "Hello";
   String str2 = "World";
   boolean isEqual = str1.equals(str2);  // isEqual的值为false
   

5. compareTo(String anotherString): Compares two strings lexicographically. A return value of 0 means equal, a positive number means the current string is greater than the parameter string, and a negative number means the current string is smaller than the parameter string.

   String str1 = "Apple";
   String str2 = "Banana";
   int result = str1.compareTo(str2);  // result的值为-1
   

6. toUpperCase() and toLowerCase(): Convert a string to uppercase or lowercase.

   String str = "Hello";
   String upperCase = str.toUpperCase();  // upperCase的值为"HELLO"
   String lowerCase = str.toLowerCase();  // lowerCase的值为"hello"
   

7. contains(CharSequence sequence): Determines whether the string contains the specified character sequence.

   String str = "Hello World";
   boolean contains = str.contains("World");  // contains的值为true
   

8. replace(CharSequence target, CharSequence replacement): Replaces the specified character sequence in the string with a new character sequence.

   String str = "Hello World";
   String replaced = str.replace("World", "Java");  // replaced的值为"Hello Java"
   

9. split() method to split a string: it accepts a regular expression as an argument and splits the string into an array of substrings

   String str = "Hello,World,Java"; String[] parts = str.split(",");  // 使用逗号分割字符串 // parts数组的值为 ["Hello", "World", "Java"]
   

   The split() method accepts a regular expression as an argument. If you want to use special characters for splitting, you need to escape them. For example, if you want to split with a period ".", you need to use "." as the delimiter.

   String str = "Hello.World.Java";
   String[] parts = str.split("\\.");  // 使用句点分割字符串
   // parts数组的值为 ["Hello", "World", "Java"]