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