Java基本的程序设计结构（一）

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前言：虽然说学过设计模式，J2EE，这个学期才开始学Java，呵呵，有点颠倒了，但是还是要从基本的抓起。hoho～～
（一）一个简单的java应用程序
Package edu.ynu.java.lession1
/
The simplest Java program
/
public class FirstJavaProg
{
    public static void main(String[] args)
    {
        // System.out is the standard output stream.
        System.out.println("Hello!");
    }
}

(二)注释
// This is my first Java program

（三）数据类型
byte (1 bytes, -128 … 127)
short (2 bytes, -32,768 … 32,767)
int (4 bytes, -2,147,483,648 … 2,147,483,647)
long (8 bytes)
Integer literals can be specified in several bases:
    Decimal — -99 or 32174
    Octal — 012 or 07
    Hexadecimal — 0xff or 0XABCDEF01
float
    4 bytes
    6.5 significant digits
    ±3.4028E+38F
    denoted by ‘F’ or ‘f’ suffix
double
    8 bytes
    15 significant digits
    ±1.7977E+308
    denoted by ‘D’ or ‘d’ suffix (or no suffix)

    if (Double.isNaN(x)) // check whether x is "not a number"

boolean
char

（四）变量
赋值和初始化
常量
Example：
public class Constants
{
   public static void main(String[] args)
   {
     final double CM_PER_INCH = 2.54;
      double paperWidth = 8.5;
      double paperHeight = 11;
      System.out.println("Paper size in centimeter: "
         + paperWidth CM_PER_INCH + " by "
         + paperHeight CM_PER_INCH);
   }
}

（五）运算符
Arithmetic +, -, *, /, and %.
Prefix and postfix ++ and –.
Boolean ==, !=, <, <=, >, >=, &&, and ||.
Bitwise &, |, ^, and ~.
Arithmetic shift << and >>.
Logical shift >>>.

Java logical operators
&&   (conditional AND)
&     (boolean logical AND)
||   (conditional OR)
|     (boolean logical inclusive OR)
^     (boolean logical exclusive OR)
!     (logical NOT)

数学函数和常量
Constants (e.g, Math.PI)
Functions (e.g., Math.sin())
数值类型之间的转换


强制类型转化
double x = 9.997;
int nx = (int)Math.round(x);

括号和运算符级别
如记不得可以使用括号

枚举类型
enum Size{SMALL， MEDIUE， LARGE， EXTRA——LARGE}；
Size s = Size.SMALL;

注：变量用小写字母开头，常量和类名用大写字母开头