Class Library

Object
  Library

public class Library

extends Object

Convenience calls for using the Kernel. Each function in this class makes a system call. Sometimes, the arguments are manipulated to make their user representation more convenient. Note that this class contains only static methods. All methods return integers. Negative return values are error codes. Some methods return positive values; others simply return 0 to mean "ok".

See Also:

Kernel

Field Summary

static String[]

errorMessage A table of error messages corresponding to Kernel error return codes.

Constructor Summary

private

Library() This private constructor ensures that no instances of Library are ever created.

Method Summary

static int	exec(String command, String[] args) Performs SYSCALL_EXEC.
static int	input(StringBuffer result) Performs SYSCALL_INPUT.
static int	join(int pid) Performs SYSCALL_JOIN.
static int	output(String s) Performs SYSCALL_OUTPUT.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

errorMessage

public static final String[] errorMessage

A table of error messages corresponding to Kernel error return codes. This table should be indexed by the negative of rc, where

          rc = Kernel.interrupt(Kernel.INTERRUPT_USER, ... )
 

and rc is less than 0.

Constructor Detail

Library

private Library()

This private constructor ensures that no instances of Library are ever created.

Method Detail

output

public static int output(String s)

Performs SYSCALL_OUTPUT. Displays text on the console.

Parameters:

s - a String to display

Returns:

zero

input

public static int input(StringBuffer result)

Performs SYSCALL_INPUT. Waits for the user to type some text and hit [return]. The input line is returned in the supplied StringBuffer

Parameters:

result - a place to put the result

Returns:

zero on success, or one of the error codes Kernel.END_OF_FILE or Kernel.ERROR_IO.

exec

public static int exec(String command,
                       String[] args)

Performs SYSCALL_EXEC. Launchs the named program, and lets it run in parallel to the current program.

Parameters:

command - The name of a Java class to execute.

args - The arguments to give the new program

Returns:

a non-negative process id, or ERROR_BAD_COMMAND.

join

public static int join(int pid)

Performs SYSCALL_JOIN. Waits for a process to terminate

Parameters:

pid - a process id returned by a previous call to exec.

Returns:

zero or ERROR_NO_SUCH_PROCESS