Java Interger

1. http://www.leepoint.net/notes-java/data/basic_types/21integers.html

 

Four (or five) kinds of primtive integers and two integer classes.

Primitive types.  The are four types of integers in Java:byte, short, int, long. 

The most common is int. All integers are stored in signed, two's-complement, format.

char!  Technically, char is an unsigned integer type altho it is almost exclusively used to store characters.  Making it integer is largely because of Java's legacy from  C++.  Don't use char for integers unless you are sure of what you're doing.

Classes.  In addition to the primitive types, there are two classes used for integers.

• Integer - Primarily useful for utility methods and to put in the Collections data structure classes.
• BigInteger - Used where unbounded arithmetic is important.

How Java stores integers in memory

Java stores all integers in memory as binary numbers.

 

type	Size		Range
name	bytes	bits	minimum	maximum
byte	1	8	-128	+127
short	2	16	-32,768	+32,767
int	4	32	-2,147,483,648	+2,147,483,647
long	8	64	-9,223,372,036,854,775,808	+9,223,372,036,854,775,807

 

2.http://nannan408.iteye.com/blog/1255315

int和long都是很循规蹈矩的符合2的n次方的说法,int是32位，long是64位，唯有float和double像两个淘气的小孩子让人会捉摸不透。float和double的表示形式与int和long是不一样的，他们采用的是IEEE 754标准,这个标准可以这样理解:

(1)两者还是32位的，和int一样,最小值只是他们的精度，是正数，这是需要注意的。如果要取到他们负最大，在他们的最大值前加个符号就好了,如-Float.MAX_VALUE,就是float能表示的负的最大了。

(2)float从左到右，第一位是符号位,2-9位共8位表示整数位，2的8-1次方等于128,后面23位是表示小数的，所以最大值是2^128-1;

(3)double从左到右，第一位是符号位，2-12是共11位表示整数位，2的11-1次方等于1024。剩余20位表示小数,所以最大值是2^1024-1.

(4)如上面代码，当正的最大减去负的正最大，就产生了内存泄露。溢出的结果是不对的。

总结:int 和long，float和double的存储要分别对待.要取到实实在在的最大最小值，只需要取到最大值就行了。