Java notes--common classes

1. String class:

--Using Unicode character encoding, one character occupies two bytes;

The--string class is a final class that represents an immutable sequence of characters;

--The string is immutable, and once a string object is configured, its contents are immutable;

--Common method: 1) int length ();//return string length

2) char charAt (int index);//Returns the character of the string at index

3) int compareTo (String str);//compare with str size

4) int indexOf (string s);//Returns the position where s first appears in the string, or 1 if it does not appear.

5) int IndexOf (string s, int startPoint);//Returns the position of the first occurrence of the string after StartPoint, or 1 if it does not appear.

6) int lastIndexOf (string s);//Returns the position of the last occurrence of the string, or 1 if it does not appear.

7) int LastIndexOf (string s, int startPoint);//Returns the position of the last occurrence of the string after StartPoint, or 1 if it does not appear.

8) Boolean startwith (string prefix);//Determine if the string starts with prefix

9) Boolean endwith (string, suffix);//Determine if the string ends with suffix

A Boolean equals (Object obj);//Compare two strings for equality

One) boolean regionmatches (int firststart, String other, int otherstart, int length);// Determines whether the substring of the current string starting with Firststart is equal to the substring of the other string starting at Otherstart and length

String subString (int startPoint);//returns the substring after the string startPoint

String subString (int start, int end);//The substring that returns the string from start to end (left closed right)

() string trim ();//Returns the string after the string is removed before and after a space

String[] Split (string regex);//Use a regex delimiter to slice the string and return an array of strings

2. StringBuffer class: Variable sequence of characters

--Common methods: 1) added: Append (String | int | boolean | ...);

2) Insert: Insert (int index, string str);//Inserts the string str at the specified position index

3) Inversion: reverse ();

4) Delete: delete (int start, int end);//Remove string of specified interval

5) charAt (int index);

6) Setcharat (int index, char ch);//Modify the character at index to CH

7) Wait for a similar method as String.

3, StringBuilder class: JDK5.0 newly added, thread unsafe, efficiency is higher than stringbuffer, usage and stringbuffer similar.

4. Time-date-related classes:

Currenttimemillis () under the--system category;

--date class: Java.util.Date, Java.sql.Date

--simpledateformat class: Java.text.SimpleDateFormat

--calendar class

5. Math class: Java.lang.Math, provides a series of static methods for scientific calculations (such as ABS (), sqrt (), etc.)

Java notes--common classes