Java Learning Note (2015.7.20~24)

Java Learning Note (2015.7.20~24) Java Learning Note (2015.7.20~24)

Java

• Java Learning Note (2015.7.20~24)

  • 1, the difference between StringBuffer and StringBuilder:

  • 2. Basic data type packing class

  • 3, date, Calendar, DateFormat and other time-related classes

  • 1. Common type String

  • 2. Regular expressions

  • 3, the common class StringBuffer represents the variable character sequence

  • Unpacking and Packing

  • Application of Packaging class

  • Anonymous inner class

  • Array

  • Day11

  • Day12

  • Day13

  • Day14

Day11

• The parent class uses a method that is defined by public, and the child class must have access to public

• Members of private definition can only use their own

• Overwrite the method can expand permissions, such as Default>public, can not reduce permissions, will error

• The private method cannot inherit from the quilt class, but it can be called by the parent class's method

• Declare member variables, add a m before the general name

• In an abstract class, you can define a constructor method.

• The abstract method in the interface must be defined as public permission, not write is public

• Transition up, parent class to child class

• Similarities and differences between interfaces and abstract classes

• Familiarity with anonymous internal classes

• Interfaces are made up of global constants and abstract methods, so

• String AUTHOR = "Jensen"; equivalent to public static final String AUTHOR = "Jensen";

• void print (); equivalent to public abstract void print ();

• String GetInfo (); equivalent to public abstract String getInfo ();

• Java allows an interface to inherit multiple interfaces:
  Interface sub-interface extends parent interface A, parent interface B, ... { }

• Object Instanceof Class returns a Boolean type

• Abstract class Authoring templates

• Interface Development Standards

• Design mode Factory mode
  By adding a transition between the interface and the subclass, an instantiated object of the interface is obtained through this transition side, which is generally called the factory class.

• "Orange". Equals (ClassName) Why write string constants in front of string judgments?
  A: This avoids null-pointing exceptions, such as when an incoming value is null

Array

Arrays can be seen as multiple combinations of the same type of data
Array variable belongs to reference type

One-dimensional arrays
Declaration of an array
Int[] A; It is recommended to use this
Byte[] C;
int b[];
Attention:
Cannot specify its length when declaring an array in the Java language

Initialization
Static initialization
int b[] = new int[]{1,2,3,4,5};//static initialization
Int[] C = {1,2,34,56,7};//static initialization
Dynamic initialization

To take a value from an array according to the subscript: can be an integer constant or an integral type expression
Subscript starting from 0

Print all elements of an array in the console

Each array has a property length that indicates its lengths

Sort:
Bubble Sort Select Sort Insert Sort Hill sort

Sort:
Replace
if (A[i]>=a[j]) {
int temp = A[i];
A[i] = A[j];
A[J] = temp;
}

Two-dimensional arrays
A two-dimensional array can be seen as an array of elements
Statement
Int[][] A
int b[][]
Initialization
int b[][] =
{{1,2},{2,2,3,45,6},{2,3,6,7}};
Int[][] C =
New int[][]{{1,2},{2,2,3,45,6},{2,3,6,7}};

Two-bit array initialization
First initialize the high-dimensional
Int[][] A = {{1,23,4},{1,3,4},{2222}};

DAY12 Unpacking and Packing

int x = 30;integer i = new Integer (x);//boxing int y = I.intvalue ();//Unpacking

Application of Packaging class

• The most common use of wrapper classes in practice is to make a string into a primitive data type, such as a string of all numbers into an int or float type of data.

String str1 = "30"; String str2 = "30.3"; int x = Integer.parseint (str1); float f = float.parsefloat (STR2);

Anonymous inner class

The interface itself cannot be instantiated directly, so there is a brace after the interface instantiation in which to write the specific implementation method.

Anonymous strings are placed inside data segment

string, Length () method
Object, Length Property

day131, Common class String2, regular expressions

• Format not to be remembered

• A period. Represents a single character

• square brackets [] indicate that a single character may appear in the character set

• Parentheses () can represent multiple characters

• Curly Braces {} indicates the number of times

• Escape character "\"

• General regular expressions are made up of wildcards and fixed characters

• Chestnuts:
  

  • Letter _ number greater than 6 less than 10 bits
    "\w{6,10}"

  • Email: [Email protected]
    "\[email protected]\w+\.\w+"

  • Mobile: Starting at 13 15 18 17 11-bit
    "[1][3578]\d{9}"

Just remember:
Pattern p = pattern.compile ("A*b");
Matcher m = P.matcher ("Aaaaab");
Boolean B = m.matches ();

3, the common class StringBuffer represents the variable character sequence

String
StringBuffer

Reverse ()

Note: StringBuffer default capacity 16;
If the amount of incoming data is greater than the current capacity
StringBuffer capacity will change before the volume + 2

The difference between day141, StringBuffer and StringBuilder:

• StringBuffer: Synchronization thread security is less efficient

• StringBuilder: Asynchronous insecure single-threaded high efficiency

2. Basic data type packing class

• base data Type	wrapper class
  boolean	boolean
  byte	by Te
  char	Character
  short	Shor T
  int	Integer
  long	long
  float	float
  double	double

• Integer

  • public static int parseint (string s)

  • public static Integer valueOf (string s)

  • java5.0 after the automatic unboxing function, as follows

Integer i = new Integer (+), int j = i + 100;//automatic unpacking int k = 100;integer m = k; Automatic Boxing

• Character
  Isuppercase (char ch) determines whether a character is uppercase
  Islowercase (char ch) to determine if a character is a lowercase letter
  Isletter (char ch) determines whether a character is a letter
  IsDigit (char ch) determines whether a character is a number

3, date, Calendar, DateFormat and other time-related classes

import java.text.parseexception;import java.text.simpledateformat;import java.util.calendar; import java.util.date;public class test {         Public static void main (String[] args)  {             //  Create date format objects                      SimpleDateFormat format = new  SimpleDateFormat ("yyyy mm month DD Day  HH:MM:SS");                     try {                              date date = format.parse ("November 11, 2011  11:11:11");                              system.out.println (Date.gettime ());              } catch  (parseexception e)  {                   e.printstacktrace ();                       }                      //  Create a Calendar object                       calendar calendar = calendar.getinstance ();                       int  Year = calendar.get (calendar.year);                      system.out.println ("year = "   + year);                      int month = calendar.get (Calendar.month);                       System.out.println ("month = "  +  (month + 1));                     int day =  calendar.get (Calendar.day_of_month);                      system.out.println ("day = "  +  Day);     }   } 

Output Result:
1320981071000//Number of milliseconds from 1970 to that point in time
Year = 2015//print today's date
month = 7
Day = 25

Java Learning Note (2015.7.20~24)