The Java System class common method

1. Definitions

• public final class System is final modification, it said it could not be inherited
• private System () method of privatization, it said it could not create an instance
• All methods are all static modified

2, a common method

System.getProperty(String key)

Where key parameters are the following:

• user.dir
  current working directory project or module
• user.home
  the current user's home directory, Windows forms: C: \ Users \ Rongdi
• user.name
  current user name
• line.separator
  line break points, that is the end of the line break our file
• file.separator
  path separator, the systems are not the same, win \
• java.version
  system version

System.exit(int status)

提前退出，后面的代码不再执行，我们可以通过设置不同的状态值来标明程序是否正常退出。

System.currentTimeMillis()

返回操作系统当前的毫秒时间戳
这个在爬虫中会经常看到，作为js加密的一种手段
长度为13位，所以在爬虫中看到了一个13位的数字，第一时间就应该想到是时间戳

System.arraycopy(src, start, dest, start, end)

实现数组的拷贝，其中的start和end均为索引，且是左闭又开的

3, FIG mind summarized as follows