java的基本类型的长度

byte 1字节

short 2字节

int 4字节

long 8字节

float 4字节

double 8字节

char 2字节

boolean 是平台相关的

Oracle版：This means a boolean is usually a 32-bit variable. However arrays of booleans are treated as arrays of bytes, so booleans are 8 bits in an array"

sun版：可以参看这个文章。System.gc() doesn't guarantee cleaning memory. It just gives an order to the JVM to run the garbage collection, but it doesn't mean that the collector actually cleaned something. 

需要注意的问题是，不管操作系统的位数是多少，基本类型的长度都是固定的。Java程序不是直接运行在本地操作系统上，而是运行在JVM上，JVM将class程序不同的操作系统下的基础类型长度固定。