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)