runtime.java

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/*
 * @(#)Runtime.java	1.26 97/02/24
 * 
 * Copyright (c) 1995, 1996 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 * 
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 * 
 * CopyrightVersion 1.1_beta
 * 
 */

package java.lang;

import java.io.*;
import java.util.StringTokenizer;

/*
 * Every Java application has a single instance of class 
 * <code>Runtime</code> that allows the application to interface with 
 * the environment in which the application is running. The current 
 * runtime can be obtained from the <code>getRuntime</code> method. 
 * <p>
 * An application cannot create its own instance of this class. 
 *
 * @author  unascribed
 * @version 1.26, 02/24/97
 * @see     java.lang.Runtime#getRuntime()
 * @since   JDK1.0
 */
public class Runtime {
    private static Runtime currentRuntime = new Runtime();
      
    /**
     * Returns the runtime object associated with the current Java application.
     *
     * @return  the <code>Runtime</code> object associated with the current
     *          Java application.
     * @since   JDK1.0
     */
    public static Runtime getRuntime() { 
	return currentRuntime;
    }
    
    /** Don't let anyone else instantiate this class */
    private Runtime() {}

    /* Helper for exit
     */
    private native void exitInternal(int status);

    /**
     * Terminates the currently running Java Virtual Machine. This 
     * method never returns normally. 
     * <p>
     * If there is a security manager, its <code>checkExit</code> method 
     * is called with the status as its argument. This may result in a 
     * security exception. 
     * <p>
     * The argument serves as a status code; by convention, a nonzero 
     * status code indicates abnormal termination. 
     *
     * @param      status   exit status.
     * @exception  SecurityException  if the current thread cannot exit with
     *               the specified status.
     * @see        java.lang.SecurityException
     * @see        java.lang.SecurityManager#checkExit(int)
     * @since      JDK1.0
     */
    public void exit(int status) {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkExit(status);
	}
	exitInternal(status);
    }

    /**
     * Enable or disable finalization on exit; doing so specifies that the
     * finalizers of all objects that have finalizers that have not yet been
     * automatically invoked are to be run before the Java runtime exits.
     * By default, finalization on exit is disabled.  An invocation of
     * the runFinalizersOnExit method is permitted only if the caller is
     * allowed to exit, and is otherwise rejected by the security manager.
     * @see Runtime#gc
     * @see Runtime#exit
     * @since   JDK1.1
     */
    public static void runFinalizersOnExit(boolean value) {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    try { security.checkExit(0); }
	    catch (SecurityException e) {
		throw new SecurityException("runFinalizersOnExit");
	    }
	}
	runFinalizersOnExit0(value);
    }

    /*
     * Private variable holding the boolean determining whether to finalize
     * on exit.  The default value of the variable is false.  See the comment
     * on Runtime.runFinalizersOnExit for constraints on modifying this.
     */
    private static native void runFinalizersOnExit0(boolean value);

    /* Helper for exec
     */
    private native Process execInternal(String cmdarray[], String envp[]) 
	 throws IOException;

    /**
     * Executes the specified string command in a separate process. 
     * <p>
     * The <code>command</code> argument is parsed into tokens and then 
     * executed as a command in a separate process. This method has 
     * exactly the same effect as <code>exec(command, null)</code>. 
     *
     * @param      command   a specified system command.
     * @return     a <code>Process</code> object for managing the subprocess.
     * @exception  SecurityException  if the current thread cannot create a
     *             subprocess.
     * @see        java.lang.Runtime#exec(java.lang.String, java.lang.String[])
     * @since      JDK1.0
     */
    public Process exec(String command) throws IOException {
	return exec(command, null);
    }

    /**
     * Executes the specified string command in a separate process with the 
     * specified environment. 
     * <p>
     * This method breaks the <code>command</code> string into tokens and 
     * creates a new array <code>cmdarray</code> containing the tokens; it 
     * then performs the call <code>exec(cmdarray, envp)</code>. 
     *
     * @param      command   a specified system command.
     * @param      envp      array containing environment in format
     *                       <i>name</i>=<i>value</i>
     * @return     a <code>Process</code> object for managing the subprocess.
     * @exception  SecurityException  if the current thread cannot create a
     *               subprocess.
     * @see        java.lang.Runtime#exec(java.lang.String[], java.lang.String[])
     * @since      JDK1.0
     */
    public Process exec(String command, String envp[]) throws IOException {
	int count = 0;
	String cmdarray[];
 	StringTokenizer st;

	st = new StringTokenizer(command);
 	count = st.countTokens();

	cmdarray = new String[count];
	st = new StringTokenizer(command);
	count = 0;
 	while (st.hasMoreTokens()) {
 		cmdarray[count++] = st.nextToken();
 	}
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkExec(cmdarray[0]);
	}
	return execInternal(cmdarray, envp);
    }

    /**
     * Executes the specified command and arguments in a separate process.
     * <p>
     * The command specified by the tokens in <code>cmdarray</code> is 
     * executed as a command in a separate process. This has exactly the 
     * same effect as <code>exec(cmdarray, null)</code>. 
     *
     * @param      cmdarray   array containing the command to call and
     *                        its arguments.
     * @return     a <code>Process</code> object for managing the subprocess.
     * @exception  SecurityException  if the current thread cannot create a
     *               subprocess.
     * @see        java.lang.Runtime#exec(java.lang.String[], java.lang.String[])
     * @since      JDK1.0
     */
    public Process exec(String cmdarray[]) throws IOException {
	return exec(cmdarray, null);
    }

    /**
     * Executes the specified command and arguments in a separate process
     * with the specified environment. 
     * <p>
     * If there is a security manager, its <code>checkExec</code> method 
     * is called with the first component of the array 
     * <code>cmdarray</code> as its argument. This may result in a security 
     * exception. 
     * <p>
     * Given an array of strings <code>cmdarray</code>, representing the 
     * tokens of a command line, and an array of strings <code>envp</code>, 
     * representing an "environment" that defines system 
     * properties, this method creates a new process in which to execute 
     * the specified command. 
     *
     * @param      cmdarray   array containing the command to call and
     *                        its arguments.
     * @param      envp       array containing environment in format
     *                        <i>name</i>=<i>value</i>.
     * @return     a <code>Process</code> object for managing the subprocess.
     * @exception  SecurityException  if the current thread cannot create a
     *               subprocess.
     * @see     java.lang.SecurityException
     * @see     java.lang.SecurityManager#checkExec(java.lang.String)
     * @since   JDK1.0
     */
    public Process exec(String cmdarray[], String envp[]) throws IOException {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkExec(cmdarray[0]);
	}
	return execInternal(cmdarray, envp);
    }

    /**
     * Returns the amount of free memory in the system. The value returned
     * by this method is always less than the value returned by the
     * <code>totalMemory</code> method. Calling the <code>gc</code> method may
     * result in increasing the value returned by <code>freeMemory.</code>
     *
     * @return  an approximation to the total amount of memory currently
     *          available for future allocated objects, measured in bytes.
     * @since   JDK1.0
     */
    public native long freeMemory();

    /**
     * Returns the total amount of memory in the Java Virtual Machine. 
     *
     * @return  the total amount of memory currently available for allocating
     *          objects, measured in bytes.
     * @since   JDK1.0