public class SimpleTest
{
public static void main(String[] args)
{
System.out.println("Hello world");
}
}
1、JAVA语言是大小写敏感的。
2、程序是从MAIN（）开始执行。MAIN（）必须是public 的
JAVA中的数据类型
整 型
|
Type |
Storage Requirement |
Range (Inclusive) |
|
Int |
4 bytes |
–2,147,483,648 to 2,147,483, 647 (just over 2 billion) |
|
Short |
2 bytes |
–32,768 to 32,767 |
|
Long |
8 bytes |
–9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 |
|
Byte |
1 byte |
–128 to 127 |
实 型
|
Type |
Storage Requirement |
Range |
|
float |
4 bytes |
approximately ±3.40282347E+38F (6–7 significant decimal digits) |
|
double |
8 bytes |
approximately ±1.79769313486231570E+308 (15 significant decimal digits) |
char型
In Java, the char type describes a code unit in the UTF-16 encoding.
boolean型 true false
变量
1、 声名：变量类型：变量名；
例：double salary;
int age;
2、初始化
变量必须初始化后才能使用。
注：变量声名可以在任何地方。
常量：
在java中用final表示一个常量
例：
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 centimeters: "
+ paperWidth * CM_PER_INCH + " by " + paperHeight * CM_PER_INCH);
}
}