Java. Lang. System

Package java. Lang;

Import java. Io .*;
Import java. util. properties;
Import java. util. propertypermission;
Import java. util. stringtokenizer;
Import java. Security. accesscontroller;
Import java. Security. privilegedaction;
Import java. Security. allpermission;
Import sun.net. inetaddresscachepolicy;
Import sun. Reflect. reflection;
Import sun. Security. util. securityconstants;

/**
*
* The system class provides standard input, standard output, and standard error output, and provides the ability to obtain system attributes.
* It provides the ability to load files and link libraries, as well as a local method for copying arrays quickly. All of its methods are static
*
* Comment by liqiang
*
* @ Author Arthur van hoff
*
*/
Public final class system {
Private Static native void registernatives ();
Static {
Registernatives ();
}

// Private constructor, which has no instances
Private system (){
}

// Use NULL for initialization. If currenttimemillis is not greater than 0, an exception is thrown.
// Indicates the standard input.
Public final static inputstream in = nullinputstream ();

// Use NULL for initialization. If currenttimemillis is not greater than 0, an exception is thrown.
// Indicates the standard output.
Public final static printstream out = nullprintstream ();

// Use NULL for initialization. If currenttimemillis is not greater than 0, an exception is thrown.
// Indicates the standard error output.
Public final static printstream err = nullprintstream ();

// Security Manager
Private Static securitymanager SECURITY = NULL;

/**
*
* Reset standard input
*
*/
Public static void setin (inputstream in ){
// Security check
Checkio ();
 
// Reset the standard input local method
Setin0 (in );
}

/**
*
* Reset standard output
*
*/
Public static void setout (printstream out ){
// Security check
Checkio ();
 
// Reset the local method of standard output
Setout0 (out );
}

/**
*
* Reset standard output
*
*/
Public static void seterr (printstream ERR ){
// Security check
Checkio ();
 
// Reset the local method of standard output
Seterr0 (ERR );
}

Private Static void checkio (){
// Security check
If (Security! = NULL)
Security. checkpermission (New runtimepermission ("setio "));
}

// Reset the standard input local method
Private Static native void setin0 (inputstream in );
// Reset the local method of standard output
Private Static native void setout0 (printstream out );
// Reset the local method of standard error output
Private Static native void seterr0 (printstream ERR );

/**
*
* Set security manager
*
*/
Public static
Void setsecuritymanager (final securitymanager s ){
Try {
// Can I process the "Java. Lang" package?
S. checkpackageaccess ("Java. Lang ");
} Catch (exception e ){
// Null operation
}

// Set the security manager
Setsecuritymanager0 (s );
}

Private Static synchronized
Void setsecuritymanager0 (final securitymanager s ){
If (Security! = NULL ){
// Check whether the current security manager has the ability to change the security manager.
Security. checkpermission (New runtimepermission
("Setsecuritymanager "));
}

If (S! = NULL) & (S. getclass (). getclassloader ()! = NULL )){
Accesscontroller. doprivileged (New privilegedaction (){
Public object run (){
S. getclass (). getprotectiondomain (). implies
(Securityconstants. all_permission );
Return NULL;
}
});
}

Security = s;
Inetaddresscachepolicy. setifnotset (inetaddresscachepolicy. Forever );
}

/**
*
* Obtain the security manager
*
*/
Public static securitymanager getsecuritymanager (){
Return security;
}

/**
*
* Number of milliseconds from January 1, 1970 UTC to the current time
*
*/
Public static native long currenttimemillis ();

/**
*
* Copy the elements of the source array to the target array.
*
* @ Param SRC Source Array
* @ Param srcpos start position of source array copy
* @ Param DEST target array
* @ Param destpos start position of the target array
* @ Param length: Number of copies
*
*/
Public static native void arraycopy (Object SRC, int srcpos,
Object DEST, int destpos,
Int length );

/**
*
* Returns the hashcode value of object X, regardless of whether the actual class of object X has overwritten the hashcode method.
* Return the return value of the hashcode method of the original object. If the object is null, return 0.
*
*/
Public static native int identityhashcode (Object X );

/**
*
* System attribute. the following objects must be set.
*
* The following attributes should be set
* Java. Version: Java version, for example, 1.4.2 _ 05
* Java. Vendor: vendor of Java, such as Sun Microsystems Inc.
* Java. Vendor. url: Java vendor URL for example: http://java.sun.com/
* Java. Home: the location of the Java Runtime Environment, for example, C:/j2sdk1.4.2 _ 05/JRE.
* Java. Class. Version: the version of the Java class file, for example, 48.0.
* Java. Class. Path: The classpath environment variable set by the system.
* OS. Name: Operating System name, for example, Windows 2000
* OS. Arch: operating system architecture, for example, x86
* OS. Version: operating system version, for example, 5.0
* File. separator: file separator example :/
* Path. separator: path separator example :;
* Line. separator: line break for example: "/N"
* User. Name: user name, for example, Administrator
* User. Home: the user's home path, for example, C:/Documents and Settings/Administrator
* User. dir: current working path, for example, D:/Eclipse/workspace/test
*/
Private Static Properties props;

// Use a properties to initialize the system variable
Private Static native properties initproperties (properties props );

/**
*
* Obtain all system attributes.
*
*/
Public static properties getproperties (){
// Security check
If (Security! = NULL ){
Security. checkpropertiesaccess ();
}
 
Return props;
}

/**
*
* Set System Properties
*
*/
Public static void setproperties (properties props ){
// Security check
If (Security! = NULL ){
Security. checkpropertiesaccess ();
}
 
If (props = NULL ){
// If props is empty, initialize it through null Properties
Props = new properties ();
Initproperties (props );
}


System. Props = props;
}

/**
*
* Obtain the corresponding attributes using the key.
*
*/
Public static string getproperty (string key ){
// If the key is null or a Null String, an exception is thrown.
If (Key = NULL ){
Throw new nullpointerexception ("key can't be null ");
}
If (key. Equals ("")){
Throw new illegalargumentexception ("key can't be empty ");
}
 
// Security check
If (Security! = NULL ){
Security. checkpropertyaccess (key );
}
Return props. getproperty (key );
}

/**
*
* Get the attribute value through the key
*
* @ Param key: key value of the property
* @ Param def default value of the attribute
*
*/
Public static string getproperty (string key, string DEF ){
If (Key = NULL ){
Throw new nullpointerexception ("key can't be null ");
}
If (key. Equals ("")){
Throw new illegalargumentexception ("key can't be empty ");
}
 
If (Security! = NULL ){
Security. checkpropertyaccess (key );
}
 
Return props. getproperty (Key, DEF );
}

/**
*
* Set the value of the specified attribute
*
*/
Public static string setproperty (string key, string value ){
If (Key = NULL ){
Throw new nullpointerexception ("key can't be null ");
}
If (key. Equals ("")){
Throw new illegalargumentexception ("key can't be empty ");
}
If (Security! = NULL)
Security. checkpermission (New propertypermission (key,
Securityconstants. property_write_action ));
Return (string) props. setproperty (Key, value );
}

/**
*
* @ Deprecated
*
*/
Public static string getenv (string name ){
Throw new error ("getenv no longer supported, use properties and-D instead:" + name );
}

/**
*
* Log out of the VM.
*
* @ Param status code, indicating 0
* @ Throws securityexception
*
*/
Public static void exit (INT status ){
// Actually call the corresponding method of Runtime
Runtime. getruntime (). Exit (Status );
}

/**
*
* Manual garbage collection
*
*/
Public static void GC (){
// Actually call the corresponding method of Runtime
Runtime. getruntime (). GC ();
}

/**
*
* Call the Finalize method of all invalid objects
*
*/
Public static void runfinalization (){
// Actually call the corresponding method of Runtime
Runtime. getruntime (). runfinalization ();
}

/**
* @ Deprecated
*/
Public static void runfinalizersonexit (Boolean value ){
// Actually call the corresponding method of Runtime
Runtime. getruntime (). runfinalizersonexit (value );
}

/**
*
* Loads a code file with the specified filename from the local file
* System as a dynamic library. The filename
* Argument must be a complete path name.
*
*/
Public static void load (string filename ){
// The actual call is the runtime method.
Runtime. getruntime (). load0 (getcallerclass (), filename );
}

/**
*
* Load the dynamic link library
*
*/
Public static void loadlibrary (string libname ){
Runtime. getruntime (). loadlibrary0 (getcallerclass (), libname );
}

/**
* Maps a library name into a platform-specific string representing
* A Native library.
*/
Public static native string maplibraryname (string libname );

Private Static inputstream nullinputstream () throws nullpointerexception {
// Normal return null
If (currenttimemillis ()> 0)
Return NULL;
 
// Currenttimemillis not greater than 0 throw an exception
Throw new nullpointerexception ();
}

Private Static printstream nullprintstream () throws nullpointerexception {
// Normal return null
If (currenttimemillis ()> 0)
Return NULL;
 
// Currenttimemillis not greater than 0 throw an exception
Throw new nullpointerexception ();
}

/**
* Initialize the system class. Called after thread initialization.
*
* Initialize the system class, called after the thread Initialization
*/
Private Static void initializesystemclass (){
// Create an empty properties and assign it to the current property object
Props = new properties ();
// Use the default initialization system attribute
Initproperties (props );
 
Sun. Misc. version. INIT ();
 
// Initialize standard input, standard output, and standard error
Fileinputstream fdin = new fileinputstream (filedescriptor. In );
Fileoutputstream fdout = new fileoutputstream (filedescriptor. Out );
Fileoutputstream fderr = new fileoutputstream (filedescriptor. Err );
 
Setin0 (New bufferedinputstream (fdin ));
Setout0 (New printstream (New bufferedoutputstream (fdout, 128), true ));
Seterr0 (New printstream (New bufferedoutputstream (fderr, 128), true ));

Loadlibrary ("Zip ");

Terminator. Setup ();

// Set the maximum memory size
Sun. Misc. VM. maxdirectmemory ();

Sun. Misc. VM. Booted ();
}

// Obtain the caller's Class Object
Static class getcallerclass (){
// Note use of more generic reflection. getcallerclass ()
Return reflection. getcallerclass (3 );
}
}