JAVA (1)

Java Development The first step is to learn the relevant knowledge, to lay the foundation is the key, the following and small together I learn from the Java Foundation, together refueling!

The Java direction consists of three main blocks:

Java SE Desktop Development

Java EE Web Development

Java Me phone development

Java Development tools include:

Notepad

JCreator

JBuilder

Netbean

Eclipse (max)

Jdk:

JRE (Java Runtime Environment)

Java tool, Java compiler: Javac.exe java interpreter executor: Java.exe

Java class Library (more than 3,600 classes) commonly used 150

JDK API 1.6.0 (Help documentation)

Note: Public: Indicates that the class is common and there can be only one publicly class in a Java file

Class: Indicates that this is a category

Hello: Class name (the class name of the public class must be the same as the file name)

To compile a Java file:

Compiling Xx.java javac Xx.java

Execute Xx.java program Java XX

Java Virtual Machine (JVM): Bytecode files (. Class) are executed in the Java virtual machine

< simply give the. class file to someone else without having to hand over the. java File >

　　

Java Basic data type:

Integer type (byte one byte 8bit-128~127,short two bytes, int four bytes, long eight bytes)

Decimal (floating-point) type (float, double)

Boolean type (True, false)

Character type (char is two bytes, can hold Chinese characters, one char can only receive one character)

< conclusion: In Java, the arithmetic of char is treated directly as an integer corresponding to the ASCII code >

accuracy : byte<short<int<long<float<double

ImportJava.io.*; Public classdemo1{ Public Static voidMain (String []args) {Try{     //input stream, number received from keyboardInputStreamReader (system.in); BufferedReader BR=NewBufferedReader (ISR); //give a hintSystem.out.println ("Please enter the first number"); //reading a row of data from the consoleString A1=Br.readline (); System.out.println ("Please enter a second number"); String A2=Br.readline (); //put String->float            floatnum1=Float.parsefloat (A1); floatNum2=Float.parsefloat (A2); if(num1>num2) {System.out.println ("The first big One"); }      if(num1==num2) {System.out.println (Equal); }      if(num1<num2) {System.out.println ("The second big One"); }     }Catch(Exception e) {e.printstacktrace (); }   }}

Java three major Process control:

Sequential control

Branch control: Single branch, dual branch, multi-branch

(The conditional expression data type should be the same as the constant type after the case)

The available data types in switch are: Allow Byte,short,int,char,enum (enumeration), etc.

Loop control: For Loop, while loop, do While loop

Half Pyramid:

 Public classdemo3{ Public Static voidMain (String []args) {intLay=4;  for(inti=1;i<=lay;i++)      {        //Print *         for(intj=1;j<=i;j++) {System.out.print ("*"); }         //Play a line breakSystem.out.println (); }    }} 

Pyramid:

 Public classdemo3{ Public Static voidMain (String []args) {intLay=4;  for(inti=1;i<=lay;i++)     {       //Find out the law of space//1->3 2->2 3->1 4->0        for(intk=1;k<=i;k++) {System.out.print (" "); }       //Print *//1->1 2->2 3->5 4->7        for(intj=1;j<= (i-1) *2+1;j++) {System.out.print ("*"); }        //Play a line breakSystem.out.println (); }       }  }

Java object-oriented programming-classes and objects

Class name first Letter capital

The class is abstract and the object is concrete. A class is a template for an object that is an individual, instance of a class

Definition of the class:

Package name;

Class name extends parent class implements

Interface Name {

member variables;

Construction method;

Member methods;

}

Class-Class

Member method of the class-declaration

public int test (int a);/* Method declaration */

(Access modifier + data type + function name + (parameter list);)

Member methods (functions) of a class-special instructions

1. The parameter list of a method can be multiple

Class construction method: is a special method of the class, the main function is to complete the initialization of the new object

Characteristics:

1. Method name and class name are the same

2. No return value

3. When you create a new object of a class, the system automatically calls the constructor of the class to complete the initialization of the new object

A summary of the constructor methods of the class:

The constructor method name is the same as the class name

Construction method does not return a value

The main function is to complete the initialization of the new object

When you create a new object, the system automatically calls the class's construction method

A class can have more than one construction method

Each class has a default construction method

The importance of this:

 Public classdemo3_1{ Public Static voidMain (String []args) {person P=NewPerson (dog,23, "Wang");    P.showinfo (); }}//Define a humanclassperson{intAge ;     String name;  PublicPerson (intage,string name) {     //Poor readability        This. age=Age ;  This. name=name; }     //Show person Name      Public voidShowinfo () {System.out.println ("Name is:" +name); }   }

class variables

Static variables:

 Public classdemo3_2{StaticInti=1; Static{System.out.println (A); //the static zone block executes only onceI++; }    PublicDemo3_2 () {System.out.println ("B"); I++; }      Public Static voidMain (String []args) {demo3_2 T1=NewDemo3_2 ();           System.out.println (T1.I); Demo3_2 T2=NewDemo3_2 ();     System.out.println (T2.I); }} class method://Studentclassstu{intAge ;   String name; intfee; Static intTotalfee;  PublicStu (intAge,string name,intfee) {      This. age=Age ;  This. name=name; Totalfee+=fee; }      //return total tuition fee [plus static indicates that this is a class method (static method)]//rules in Java: Class variables are in principle accessed using class methods     Public Static intGettotalfee () {returnTotalfee; }  }

Note: non-static variables (class variables) cannot be accessed in class methods

Use: Class name. class name method or object name. Class Method Name

Class variables differ from instance variables:

Add static called a class variable or static variable, otherwise called an instance variable

Class variables are class-dependent, public properties

Instance variables belong to each individual object's properties

Class variables can be accessed directly through the class name. Class variable Name

JAVA (1)