First day of Java Foundation---

First day of the learning process

Java Overview "Computer-java Introduction"--------Java Classic Instance "Path environment configuration, HelloWorld"-------------Java Basics "keyword, identifier, comment, HelloWorld comment complete"

Ii. Overview of Java

keyboard Shortcuts :

CTRL + A: Select All Ctrl + C: Copy Ctrl + V: Paste ctrl+x: Cut

CTRL + Z: Undo ctrl+s: Save Windos+r:dos Command Run

Dos Command :

D: Drive letter Switch Dir: current directory file (clip) list display Md: Create directory Rd: Delete directory

CD: Enter the specified directory CD ...: Return to parent directory cd\: return root Del: Delete file (*.txt)

Exit: Exit DOS command Cls: Clear screen

Java features-cross-platform:

The Java language is cross-platform and the JVM is not cross-platform.

JRE:JVM + Class Library operating environment

JDK:JRE + Tools Development Kit

Summary: Software developed by the JDK must be run on the JRE and guaranteed across platforms by the JVM.

Third, Java Classic instance-helloworld

Environment Variables :

(1) The role of the PATH environment variable

Let the Javac and Java commands be used in any directory.

(2) Path environment variable configuration (master)

A: Modify Path only

D:\develop\Java\jdk1.7.0_45\bin; The previous path is added, separated by;

B: First create a java_home, then modify path

NEW: Java_home value is D:\develop\Java\jdk1.7.0_45 "JDK installation path"

Modified:%java_home%\bin; the previous path

Recommend the use of Plan B.

(3) configuration of CLASSPATH environment variables

Allows the specified class file to be accessed in any directory.

Tip: Configure one on the far left.;

The advantage of this is that it can be found and executed in the current directory first.

HelloWorld Source code:

/**This is the HelloWorld standard program for you to learn more about the full Java program code and comment style content includes: class, method, statement use;@author: Yu Junyong@version: v1.0 ideas: 1. Declare class with Class, class name is HELLOWORLDTEST;2, build main Main method, as the entry of the program, fixed format: public static void Main (string[] args) {}3, write output statement For output to achieve the integrity of the first program System.out.println ("actual output sentence"); Step: 1, class HelloWorldTest {}2, public static void main (string[] args) { }3, System.out.println ("actual output sentence"); 4. Correct merger*/  //Document Comments//This is the first Java program and a classic example of how Java begins to learn. Single-line Commentclasshelloworldtest{/*in the EditPlus application, blue represents the Java keyword; main is the entry for the Java program, and a program must have a Main method*/  //Multi-line comments     Public Static voidMain (string[] args) {//output statement, printed to the DOS interface, the output is: Hello WorldSystem.out.println ("Hello World"); //The following code is used to illustrate comments for debugging programs//        /*System.out.println ("Hello World"); System.out.println (' Day-day-up ');//This line double quotation mark System.out.println ("Good good study ');//This line double quote is incorrect System.ou            T.println ("Hello Java");            System.out.println ("hard")//Line missing statement Terminator; SYSTEM.OUT.PRINTLN ("Study Java"); //*/   //single-line comments, multiline comments combined with    }}

Summarize:

First, comments

1, note there are three kinds, single-line comment://

Multiline Comment:/* */

Document Comment:/** */

Note: Single-line comments can be nested, multiline comments, document annotations cannot be nested

Creative use: A multiline comment combined with a single-line comment allows for flexible management of the code, as shown in the output statement; Multiline comments can also be used to debug a program.

Code writing often occurs with an error:

1, keyword writing errors, the keywords are lowercase letters;

2, the class name is saved without regard to the suffix name, such errors occur: Demo.java.txt;

3, String/system first letter all need capital;

4, brackets do not pair, in writing, write directly pairing, and then add the middle part of the code;

5, class name, variable name, method name is not standardized, comments incomplete [professional quality].

Key words:

Are words in Java that are reserved for a particular meaning, all lowercase letters. where Goto, const is a reserved character, may be promoted to a keyword in later versions.

Identifier (zhi):

The name of the package, class, variable, method, constant.

1. Rules for identifiers:

Composed of 26 English characters "case", 1-9 numeric characters, _ and $;

Where numbers cannot be used to start identifiers;

cannot be the same as the keyword;

Strictly case-sensitive.

2, the identifier naming rules: see the name of the meaning; hump naming;

Package: Words are lowercase, multi-level package between. Connection;

Classes and interfaces: One word, first letter capital, multiple words, each word capitalized;

method, variable name: Single word, first letter lowercase, multiple words, first letter lowercase, then all the first letter of the words are capitalized;

Constants: All letters are capitalized, multiple words, and words are separated by _.

in HelloWorld Summary of errors appearing in :

1, hidden suffix name is not managed, there are a.java.txt naming errors;

2, Main method, main write Wrong (Mian);

3, System, the first letter of the string is not uppercase;

4, Chinese and English symbol inclusions, all the input are English characters;

5, all statements to; for the end of the logo, cannot but write, and must be in English mode;

6, the parentheses are paired, and need pairing.

First day of Java Foundation---