[Java] Useful Classes: Object,Class,System,Runtime

时间：2010-09-13 来源：web_surf

Package
java.lang.
Object
It is the root base class of java classes hierarchy.
Class
It is in-memory representation of Java class. This representation serves as the starting point for querying class-felated information (such as modifier(static, public\private\protected, abstract, final), field, method).

System

Operate input stream, output stream, error output stream
Get environment

Get/Set system properties
The system properties are key-value pairs. The default properties provided ty VM are:

        java.vendor.url
        java.class.path
        user.home
        java.class.version
        os.version
        java.vendor
        user.dir
        user.timezone
        path.separator
        os.name
        os.arch
        line.separator
        file.separator
        user.name
        java.version
        java.home

Load library
Copy array
Get current time
Inform VM to run garbage collection at some good time
Inform to exit VM and stop program

Runtime
- Add VM shutdown hook
- Load library
- Memory
  1. Get maximum memory
  2. Get free/total memory available for the running program
- Execute the specified program in the seperate process
- Inform to stop VM
- Inform to start garbage collection
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