Java Language Programming Design (one)

Chapter one. Introduction to JAVA

(1) Preliminary knowledge

A) Java Language specification

b) Java API

c) Java Edition:java Se,java Ee,java ME

d) Java ENVIRONMENT:JDK,JRE,JVM

e) Java Development Tools:eclipse,myeclipse,netbeans ...

Note:you can also run a Java program by using Java Command.

(2) A Simple Java Program//welcome.java

1  Public class welcome{2      Public Static void main (String [] args) {3         System.out.println ("Welcome to  Java.") ); 4     }5 }

NOTE:A) Java Source Programs is case sensitive.if The semicolon is missing.a brace was missing.a quotation mark is missing. Or String is Misspelled.thus the Java Compiler would report syntax error.

b) Procedure:edit (. java) →compile (. Class) →execute (?)

(3) A Simple Java GUI program//welcomeinmessagedialogbox.java

1 Import Javax.swing.JOptionPane; 2  Public class Welcomeinmessagedialogbox {3      Public Static void main (String [] args) {4         Joptionpane.showmessagedialog (null, "Welcome to Java.") ); 5     }6 }

Note:if you want to learn further,please refer to JAVA Api.thus your can make more beautiful GUI program.

Chapter. Elementary Programming

(1) Let us strat from programs Area.java and Areaconsoleinput.java

1  Public classArea {2      Public Static voidmain (String [] args) {3         DoubleRadius=20;4         DoubleArea ;5         6area=radius*radius*3.141596;7         8System.out.println ("The area for the Circle is" +Area );9     }Ten}

1 ImportJava.util.Scanner;2 3  Public classAreaconsoleinput {4      Public Static voidmain (String [] args) {5         Doubleradius;6         DoubleArea ;7         8Scanner input=NewScanner (system.in);9radius=input.nextdouble ();Tenarea=radius*radius*3.141596; One          ASystem.out.println ("The area for the Circle is" +Area ); -     } -}

(2) Identifies

Note:some rules must is obeyed for identifies.

A) It consists of letters,digits,underscores and dollar signs.

b) It must start with a letter, an underscore or a dollar sign.rather than a digit.

c) It can ' t be a reserved word in Java specification and Java API.

d) It can be of any length or language. Chinese is okay.however it's case sensitive.

(3) Variables

Note:by convention,variable name is in lowercase. If A name consists of several words,concatenate all of them and capitalize the first letter of each word except the first. Furthermore,we can declare a variable and initialize it in one step.

(4) Assignment Statements and Assignment Expressions

Note:firstly,we must distinguish it from equation in mathematics. Then,an assignment statement is essentially a expression that evaluates to the value to being assigned to the variable on th e Left-Hand side of assignment operator. Finally,the data type of the variable on the left must is compatible with the data type of the value on the right.

(5) Constants

note:a keyword Final is used to declaring a constant in Java.and constants often is named uppercase.

(6) Numerical Data Types and Operations

Note:we must keep the memory space for variables of different data types and their range

Please look the following examples.

1  Public classTestintrange {2      Public Static voidmain (String [] args) {3         inta=2147483647+1;//The value of a is-21474836484         intB=-2147483648-1;//The value of B is 21474836475System.out.println ("The value of A is" +a);6System.out.println ("The value of B is" +b);7     }8}

Standard arithmetic Operators:addition,substraction,multiplication,division,and remainder.

(7) Shorthand Operators

(8) Numeric Type Conversions

(9) String

(10) Programming Styles and documentation.

A) naming Styles:use lowercase for variables.

Concatenate all of them and capitalize the first letter of each word except the first for method

Capitalize the first letter of each word in a class name

Capitalize every letter in a constant.

b) Statement Styles:approximate Space and Indentation.keep block Styles.

c) Comment Styles:add some Comment in your program.

Java Language Programming Design (one)