My first acquaintance java --- a java program
Course Catalog
l ready
l environment ready to open Requested Procedure
l environment variable Path set
l First Program
aims
<< realize their HelloWorld run and see the results
One, ready
(1) Computation desk (personal computer)
(2) Computer hardware: Part naked eye can see
(3) Computer software
System Software: xp, windows, Linux, Mac
Applications: office, qq ....
(4) Language
Natural Language: interpersonal communication and exchange of
Computer Language: people and computers for communication.
C,C++,C#,Java
(5) Human-Computer Interaction
Graphical interface: just double-click easy to operate, plug-operation
DOS command: the need for some common commands memory
(6) the basic concepts of unit
The concept of bit (B: 'bit ) : is a binary data (0,1) à bit is the smallest unit of computer
Byte (B: Byte) : . 8 bits and a byte à byte is the basic unit of computer
Kilobytes (KB ) : 1KB 2 ^ 10 = B
Megabytes (MB ) : 1MB = 2 ^ 10 KB
Gigabytes (GB ) : 1GB = 2 ^ 10MB
Terabytes (the TB ) : 2 ^ = 1TB 10GB
32-bit and 64-bit operating system means: CPU processing capacity of one 32-bit data or 64-bit
Second, understanding the function keys and keyboard shortcuts
(1) understanding the function keys
tab
shift
ctrl
alt
windows
Blank
up down left right
Enter
Screenshot QQ Screenshot: Ctrl + Alt + A
(2) commonly used shortcuts
Select All Ctrl + A
Copy Ctrl + C
Paste Ctrl + V
Cut Ctrl + X
Undo Ctrl + Z
Save Ctrl + S
Recovery Ctrl + Y
Open the Start menu Win
Turn on the computer window Win + E
Open the Run window Win + R
Show Desktop / minimize all windows Win + D
Third, the common DOS commands as follows:
Switching letter: letter colon
d: Enter
Change directory: cd path plus
cd file name
Fallback directory
cd .. (to return to the parent directory)
cd \ (back to the root directory of the current disk)
Check the contents of the current directory
to you
Autofill
Tab
Use last used command
↑ ↓
Clear screen
cls
drop out
exit
Four, Java language Overview
-
- Java was born in 1995 in the sun's
- 2009 was the acquisition of oracle
- Java language: object-oriented, easy to learn
- Suitable for large enterprise-class management system, large-scale Internet system
(1) Java language nouns:
jdk: java Development Kit (Java Developlment Kit)
jre: java runtime environment (Java Runtime Enviroment)
jvm: java virtual machine (Java Virtual Machine)
Features (2) Java language
Simple and efficient, object-oriented, platform-independent.
Once, run everywhere
(3) Java language is cross-platform, may I ask is how to ensure it?
For different operating systems, by different jvm to achieve.
(4) Java language platform
JavaEE late to learn javaWeb Internet enterprise development project
JavaSE are learning basic grammar java standard edition, standard library
JavaME embedded development for the development of mobile terminals
Five, JDK, JRE, JVM's role and relationship
(1) the role of
JVM: Java language to ensure cross-platform virtual machine
JRE: Java Runtime Environment program
JDK: Java program development environment
(2) Relationship
JDK: JRE + Tools
JRE: JVM + class library
Six, JDK installation
Installation JDK step (be resolved):
Jdk official website: http: //www.oracle.com/jp/index.html
Seven, write test cases
① tested in a non-installation drive
② Create a new file Test.java
③ writing code
class HelloWorld{ public static void main(String args[]){ System.out.println("HelloWorld"); } }
④ Test.java file compiled by javac command in a DOS window, enter:
javac Test.java
⑤ run HelloWorld.class file with the java command
java Test
Eight, Frequently Asked Questions
(1) extension is hidden
How to find: Tools - Folder Options - View - remove Hide extensions
(2) We are now generally consistent file name and class name.
.java file among the class name (behind the class with the name) after after compilation, will be the class name as a .class file name.
However, note: with the javac followed by the file name extension +
With the back of java class name without extension
(3) Java language strictly case-sensitive
(4) Do not mistake the word
(5) see illegal characters:
We must all write procedures require punctuation marks in English state.
(6) pairing problems brackets.
In general, the brackets are in pairs.
(7) encountered not find the main method in the class HelloWorld
(8) forget to write back the statement semicolon