Java learns thirty (String and StringBuffer classes) from scratch, and java clears stringbuffer

Java learns thirty (String and StringBuffer classes) from scratch, and java clears stringbuffer
I. StringBuffer connection character operations when the content of a string needs to be changed frequently, use StringBuffer TO USE THE append () method in StringBuffer to complete string connection operations II. Common StringBuffer Methods

No.	Method Definition	Type	Description
1	Public StringBuffer ()	Structure	StringBuffer Constructor
2	Public StringBuffer append (char c)	Method	A large number of append operations are provided in StringBuffer (similar to "+" in String). content can be appended to StringBuffer. This method can be used to add any data types.
3	Public StringBuffer append (String str)	Method
4	Public StringBuffer append (StringBuffer sb)	Method
5	Public int indexOf (String str)	Method	Queries whether a specified string exists.
6	Public int indexOf (String str, int fromIndex)	Method	Query whether a specified string exists from the specified position
7	Public StringBuffer insert (int offset, String str)	Method	Add the specified string at the specified position
8	Public StringBuffer reverse ()	Method	Reverse save content
9	Public StringBuffer replace (int start, int end, String str)	Method	Content replacement
10	Public int length ()	Method	Obtain the Content Length
11	Public StringBuffer delete (int start, int end)	Method	Deletes a string from a specified range.
12	Public String substring (int start)	Method	String truncation, specifying the start point
13	Public String substring (int start, int end)	Method	Truncates a string from a specified range.
14	Public String toString ()	Method	Object class inheritance method, used to change the content to the String type

Iii. Use the String class

Package com. pb. demo1; public class StringTest {public static void main (String [] args) {String str = "Learn Java! "; // Length () method System. out. the length of println (str + "is:" + str. length (); // converts the case sensitivity toLowerCase (), toUpperCase () System. out. println ("to lowercase:" + str. toLowerCase (); System. out. println ("converted to uppercase:" + str. toUpperCase (); // verify whether the character J exists. int index = str. indexOf ("J"); // returns the subscript if any, and-1 System if no. out. println (index); // the character of the subString from 0 to 4, but does not contain the four-character System. out. println (str. substring (0, 4); // starts from 4 to the end of System. out. println (str. substring (4); // split String email = "wei@163.com; hao@sohu.com; aa@qq.com"; String [] emaillist = email. split (";"); // traverses the array for (String s: emaillist) {System. out. println (s );}}}

Iv. StringBuffer class

Package com. pb. demo1; public class StringBufferTest {public static void main (String [] args) {StringBuffer str = new StringBuffer ("abc_def_add_zzD "); // lookup _ the first occurrence location int indexfirst = str. indexOf ("_"); System. out. println ("location where _ appears for the first time" + indexfirst); // Add "A" str. insert (indexfirst + 1, "A"); System. out. println (str); // search for the last index location where "_" appears. int indexlast = str. lastIndexOf ("_"); System. out. println ("find the index location where the last _ appears" + indexlast); // Delete the last "_" // str. deleteCharAt (indexlast); str. delete (indexlast, indexlast + 1); System. out. println (str); System. out. println ("========================"); StringBuffer email = new StringBuffer ("rock105@sohu.com "); //// search for the index location int index = email. indexOf ("@"); email. replace (0, index, "tom"); System. out. println (email );}}