ACM path -- string processing of Stringh and StringBuffer

String common operations:

1. Use the charAt method of the String class to retrieve a certain byte. The count starts from 0:

String a = "Hello"; // a. charAt (1) = 'E'

2. Use the substring method to obtain the substring. For example

System. out. println (a. substring (0, 4) // output "Hell"

Note: The characters at the position of the substring's 2nd parameters are not included. In this way, s. substring (a, B) always contains B-a characters.

3. replaceAll) to replace the corresponding string

Public class Main {public static void main (String [] args) {String str = "dasdsad3213adasd3123"; String strTemp = str. replaceAll ("[a-zA-Z]", ""); System. out. print (strTemp); // output 32133123 }}

ReplaceAll is used to replace all English characters in the string with null characters.

4. Use the split () method to split strings

Public class Main {public static void main (String [] args) {String str = "2013/09/24"; String [] strTemp = str. split ("/"); for (int I = 0; I <strTemp. length; I ++) {System. out. print (strTemp [I] + ""); // output 2013 09 24 }}}

5. You can use the + sign for string connection, as shown in figure

String a = "Hello ";

String B = "world ";

System. out. println (a + "," + B + "! "); // Output" Hello, world! "

To directly change a byte in a string, you can use another StringBuffer class.

Difference between String and StringBuffer

String	StringBuffer
A) immutable object. Modifying existing String objects is to re-create a new object. B) assign values directly or assign values through constructors. Difference: assign values directly. First, judge whether the same string exists in the java string pool, so you do not need to redefine the sharing design ). If the constructor assigns a value, a new unit needs to be created in the memory each time. C) String overwrites the equals method and hashCode. Method. Suitable for set operations.	A) mutable object B) assign values only through Constructors C) StringBuffer does not overwrite the equals and hashCode methods. In general, StringBuffer is more efficient than String connection operations. Append) method.
Key points: 1. It is considered that append () is more efficient than "+. This is because "+" is the most efficient when compiling strings to determine the value. Example: String result = "hello" + "world"; // an object 2. Do not use new) to create a String. Because new () is used to open up new memory. 3. Avoid using "+ =" to construct a string. 4. When declaring the StringBuffer object, set the appropriate capacity. Do not use the default value 16) 5. Pay attention to the use of intern. S. intern () = t. intern () is true, if and only if s. Except st) is true. That is, the content is the same.

Conversion between string, int, and char []

String to char	Char ch [] = str. toCharArray ()
Char to String	1) String s = new String (ch ); 2) String s = ch. toString ();
String to int (this String is numeric or an error occurs during conversion)	1) Int I = Integer. parseInt (str) 2) Int I = Integer. valueOfstr). intValue;
Convert int to String	1) String s = String. valueof (I ); 2) String s = Integer. toString (I ); 3) String s = "" + I;

This article is from the blog of "Italian suckling pig", please be sure to keep this source http://lovesisi.blog.51cto.com/6414433/1301164