Every Java application has a single instance of class
Runtime
that allows the application to interface with the environment in which the application is running. The current runtime can be obtained from the
getRuntime
method.
An application cannot create its own instance of this class.
Shutdown SequenceThe Java Virtual Machine initiates the shutdown sequence in response to one of several events:
Runtime.exit or System.exit method is called for the first time; orAt the beginning of the shutdown sequence, the registered shutdown hooks are started in some unspecified order. They run concurrently with any daemon or non-daemon threads that were alive at the beginning of the shutdown sequence.
After the shutdown sequence has begun, registration and de-registration of shutdown hooks with addShutdownHook and removeShutdownHook is prohibited. However, creating and starting new threads is permitted. New threads run concurrently with the registered shutdown hooks and with any daemon or non-daemon threads that are already running.
The shutdown sequence finishes when all shutdown hooks have terminated. At this point, the Java Virtual Machine terminates as described below.
It is possible that one or more shutdown hooks do not terminate, for example, because of an infinite loop. In this case, the shutdown sequence will never finish. Other threads and shutdown hooks continue to run and can terminate the JVM via the halt method.
Prior to the beginning of the shutdown sequence, it is possible for a program to start a shutdown hook by calling its start method explicitly. If this occurs, the behavior of the shutdown sequence is unspecified.
The JVM terminates when the shutdown sequence finishes or when halt is called. In contrast to exit, the halt method does not initiate the shutdown sequence.
When the JVM terminates, all threads are immediately prevented from executing any further Java code. This includes shutdown hooks as well as daemon and non-daemon threads. This means, for example, that:
finally clauses are not executed;JNI_CreateJavaVM function to launch the JVM. Subsequently, the native code invokes the DestroyJavaVM function to await termination of that JVM. The DestroyJavaVM function is responsible for initiating the shutdown sequence when the number of live non-daemon threads first drops to zero. When the shutdown sequence completes and the JVM terminates, control is returned to the native code that invoked DestroyJavaVM. This behavior differs from the exit or halt methods. These methods typically terminate the OS process hosting the JVM and do not interact with the JNI Invocation API.
Nested Classes
static final class
A representation of a version string for an implementation of the Java SE Platform.
void
Registers a new virtual-machine shutdown hook.
int
Returns the number of processors available to the Java virtual machine.
Executes the specified command and arguments in a separate process.
Executes the specified command and arguments in a separate process with the specified environment.
Executes the specified command and arguments in a separate process with the specified environment and working directory.
void
long
Returns the amount of free memory in the Java Virtual Machine.
void
Runs the garbage collector in the Java Virtual Machine.
Returns the runtime object associated with the current Java application.
void
void
Loads the native library specified by the filename argument.
void
Loads the native library specified by the libname argument.
long
Returns the maximum amount of memory that the Java virtual machine will attempt to use.
boolean
De-registers a previously-registered virtual-machine shutdown hook.
void
long
Returns the total amount of memory in the Java virtual machine.
Methods declared in class java.lang.Objectclone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait()
Returns the runtime object associated with the current Java application. Most of the methods of class Runtime are instance methods and must be invoked with respect to the current runtime object.
Runtime object associated with the current Java application.
public void exit(int status)
Initiates the
shutdown sequenceof the Java Virtual Machine. Unless the security manager denies exiting, this method initiates the shutdown sequence (if it is not already initiated) and then blocks indefinitely. This method neither returns nor throws an exception; that is, it does not complete either normally or abruptly.
The argument serves as a status code. By convention, a nonzero status code indicates abnormal termination.
Successful invocations of this method are serialized such that only one invocation initiates the shutdown sequence and terminates the VM with the given status code. All other invocations will perform no action and block indefinitely.
Because a successful invocation of this method blocks indefinitely, if it is invoked from a shutdown hook, it will prevent that shutdown hook from terminating. Consequently, this will prevent the shutdown sequence from finishing.
The System.exit method is the conventional and convenient means of invoking this method.
java.lang.Runtime is enabled with logging level Level.DEBUG the stack trace of the call to Runtime.exit() is logged.
status - Termination status. By convention, a nonzero status code indicates abnormal termination.
SecurityException - If a security manager is present and its checkExit method does not permit exiting with the specified status
Registers a new virtual-machine shutdown hook.
A shutdown hook is simply an initialized but unstarted thread. Shutdown hooks are started at the beginning of the shutdown sequence. Registration and de-registration of shutdown hooks is disallowed once the shutdown sequence has begun.
Uncaught exceptions are handled in shutdown hooks just as in any other thread, as specified in Thread.UncaughtExceptionHandler. After the uncaught exception handler has completed, the shutdown hook is considered to have terminated and is not treated differently from a hook that has terminated without having thrown an uncaught exception.
Shutdown hooks should also finish their work quickly. When a program invokes exit, the expectation is that the virtual machine will promptly shut down and exit. When the virtual machine is terminated due to user logoff or system shutdown the underlying operating system may only allow a limited amount of time in which to shut down and exit. It is therefore inadvisable to attempt any user interaction or to perform a long-running computation in a shutdown hook.
hook - An initialized but unstarted Thread object
IllegalArgumentException - If the same hook (compared using ==) as the specified hook has already been registered, or if it can be determined that the hook is already running or has already been run
IllegalStateException - If the shutdown sequence has already begun
SecurityException - If a security manager is present and it denies RuntimePermission("shutdownHooks")
De-registers a previously-registered virtual-machine shutdown hook. Hooks are compared using ==. Registration and de-registration of shutdown hooks is disallowed once the shutdown sequence has begun.
hook - the hook to remove
true if the specified hook had previously been registered and was successfully de-registered, false otherwise.
IllegalStateException - If the shutdown sequence has already begun
SecurityException - If a security manager is present and it denies RuntimePermission("shutdownHooks")
public void halt(int status)
Immediately
terminatesthe Java Virtual Machine. If the security manager denies exiting, throws
SecurityException
. Otherwise, termination of the Java Virtual Machine is unconditional and immediate. This method does not initiate the
shutdown sequence, nor does it wait for the shutdown sequence to finish if it is already in progress. An invocation of this method never returns normally.
status - Termination status. By convention, a nonzero status code indicates abnormal termination. If the exit (equivalently, System.exit) method has already been invoked then this status code will override the status code passed to that method.
SecurityException - If a security manager is present and its checkExit method does not permit an exit with the specified status
This is a convenience method. An invocation of the form exec(command) behaves in exactly the same way as the invocation exec(command, null, null).
ProcessBuilder.start() for details.
command - a specified system command.
Process object for managing the subprocess
SecurityException - If a security manager exists and its checkExec method doesn't allow creation of the subprocess
IOException - If an I/O error occurs
NullPointerException - If command is null
IllegalArgumentException - If command is empty
This is a convenience method. An invocation of the form exec(command, envp) behaves in exactly the same way as the invocation exec(command, envp, null).
ProcessBuilder.start() for details.
command - a specified system command.
envp - array of strings, each element of which has environment variable settings in the format name=value, or null if the subprocess should inherit the environment of the current process.
Process object for managing the subprocess
SecurityException - If a security manager exists and its checkExec method doesn't allow creation of the subprocess
IOException - If an I/O error occurs
NullPointerException - If command is null, or one of the elements of envp is null
IllegalArgumentException - If command is empty
Executes the specified string command in a separate process with the specified environment and working directory.
This is a convenience method. An invocation of the form exec(command, envp, dir) behaves in exactly the same way as the invocation exec(cmdarray, envp, dir), where cmdarray is an array of all the tokens in command.
More precisely, the command string is broken into tokens using a StringTokenizer created by the call new StringTokenizer(command) with no further modification of the character categories. The tokens produced by the tokenizer are then placed in the new string array cmdarray, in the same order.
ProcessBuilder.start() for details.
command - a specified system command.
envp - array of strings, each element of which has environment variable settings in the format name=value, or null if the subprocess should inherit the environment of the current process.
dir - the working directory of the subprocess, or null if the subprocess should inherit the working directory of the current process.
Process object for managing the subprocess
SecurityException - If a security manager exists and its checkExec method doesn't allow creation of the subprocess
IOException - If an I/O error occurs
NullPointerException - If command is null, or one of the elements of envp is null
IllegalArgumentException - If command is empty
This is a convenience method. An invocation of the form exec(cmdarray) behaves in exactly the same way as the invocation exec(cmdarray, null, null).
ProcessBuilder.start() for details.
cmdarray - array containing the command to call and its arguments.
Process object for managing the subprocess
SecurityException - If a security manager exists and its checkExec method doesn't allow creation of the subprocess
IOException - If an I/O error occurs
NullPointerException - If cmdarray is null, or one of the elements of cmdarray is null
IndexOutOfBoundsException - If cmdarray is an empty array (has length 0)
This is a convenience method. An invocation of the form exec(cmdarray, envp) behaves in exactly the same way as the invocation exec(cmdarray, envp, null).
ProcessBuilder.start() for details.
cmdarray - array containing the command to call and its arguments.
envp - array of strings, each element of which has environment variable settings in the format name=value, or null if the subprocess should inherit the environment of the current process.
Process object for managing the subprocess
SecurityException - If a security manager exists and its checkExec method doesn't allow creation of the subprocess
IOException - If an I/O error occurs
NullPointerException - If cmdarray is null, or one of the elements of cmdarray is null, or one of the elements of envp is null
IndexOutOfBoundsException - If cmdarray is an empty array (has length 0)
Executes the specified command and arguments in a separate process with the specified environment and working directory.
Given an array of strings cmdarray, representing the tokens of a command line, and an array of strings envp, representing "environment" variable settings, this method creates a new process in which to execute the specified command.
This method checks that cmdarray is a valid operating system command. Which commands are valid is system-dependent, but at the very least the command must be a non-empty list of non-null strings.
If envp is null, the subprocess inherits the environment settings of the current process.
A minimal set of system dependent environment variables may be required to start a process on some operating systems. As a result, the subprocess may inherit additional environment variable settings beyond those in the specified environment. The minimal set of system dependent environment variables may override the values provided in the environment.
ProcessBuilder.start() is now the preferred way to start a process with a modified environment.
The working directory of the new subprocess is specified by dir. If dir is null, the subprocess inherits the current working directory of the current process.
If a security manager exists, its checkExec method is invoked with the first component of the array cmdarray as its argument. This may result in a SecurityException being thrown.
Starting an operating system process is highly system-dependent. Among the many things that can go wrong are:
In such cases an exception will be thrown. The exact nature of the exception is system-dependent, but it will always be a subclass of IOException.
If the operating system does not support the creation of processes, an UnsupportedOperationException will be thrown.
ProcessBuilder.start() for details.
cmdarray - array containing the command to call and its arguments.
envp - array of strings, each element of which has environment variable settings in the format name=value, or null if the subprocess should inherit the environment of the current process.
dir - the working directory of the subprocess, or null if the subprocess should inherit the working directory of the current process.
Process object for managing the subprocess
SecurityException - If a security manager exists and its checkExec method doesn't allow creation of the subprocess
UnsupportedOperationException - If the operating system does not support the creation of processes.
IOException - If an I/O error occurs
NullPointerException - If cmdarray is null, or one of the elements of cmdarray is null, or one of the elements of envp is null
IndexOutOfBoundsException - If cmdarray is an empty array (has length 0)
public int availableProcessors()
This value may change during a particular invocation of the virtual machine. Applications that are sensitive to the number of available processors should therefore occasionally poll this property and adjust their resource usage appropriately.
public long freeMemory()
Returns the amount of free memory in the Java Virtual Machine. Calling the gc method may result in increasing the value returned by freeMemory.
public long totalMemory()
Note that the amount of memory required to hold an object of any given type may be implementation-dependent.
public long maxMemory()
Returns the maximum amount of memory that the Java virtual machine will attempt to use. If there is no inherent limit then the value
Long.MAX_VALUE
will be returned.
public void gc()
Runs the garbage collector in the Java Virtual Machine.
Calling this method suggests that the Java Virtual Machine expend effort toward recycling unused objects in order to make the memory they currently occupy available for reuse by the Java Virtual Machine. When control returns from the method call, the Java Virtual Machine has made a best effort to reclaim space from all unused objects. There is no guarantee that this effort will recycle any particular number of unused objects, reclaim any particular amount of space, or complete at any particular time, if at all, before the method returns or ever. There is also no guarantee that this effort will determine the change of reachability in any particular number of objects, or that any particular number of Reference objects will be cleared and enqueued.
The name gc stands for "garbage collector". The Java Virtual Machine performs this recycling process automatically as needed, in a separate thread, even if the gc method is not invoked explicitly.
The method System.gc() is the conventional and convenient means of invoking this method.
Runs the finalization methods of any objects pending finalization. Calling this method suggests that the Java virtual machine expend effort toward running the
finalize
methods of objects that have been found to be discarded but whose
finalize
methods have not yet been run. When control returns from the method call, the virtual machine has made a best effort to complete all outstanding finalizations.
The virtual machine performs the finalization process automatically as needed, in a separate thread, if the runFinalization method is not invoked explicitly.
The method System.runFinalization() is the conventional and convenient means of invoking this method.
Loads the native library specified by the filename argument. The filename argument must be an absolute path name. (for example
Runtime.getRuntime().load("/home/avh/lib/libX11.so");
). If the filename argument, when stripped of any platform-specific library prefix, path, and file extension, indicates a library whose name is, for example, L, and a native library called L is statically linked with the VM, then the JNI_OnLoad_L function exported by the library is invoked rather than attempting to load a dynamic library. A filename matching the argument does not have to exist in the file system. See the
JNI Specificationfor more details. Otherwise, the filename argument is mapped to a native library image in an implementation-dependent manner.
First, if there is a security manager, its checkLink method is called with the filename as its argument. This may result in a security exception.
This is similar to the method loadLibrary(String), but it accepts a general file name as an argument rather than just a library name, allowing any file of native code to be loaded.
The method System.load(String) is the conventional and convenient means of invoking this method.
filename - the file to load.
SecurityException - if a security manager exists and its checkLink method doesn't allow loading of the specified dynamic library
UnsatisfiedLinkError - if either the filename is not an absolute path name, the native library is not statically linked with the VM, or the library cannot be mapped to a native library image by the host system.
NullPointerException - if filename is null
Loads the native library specified by the
libname
argument. The
libname
argument must not contain any platform specific prefix, file extension or path. If a native library called
libname
is statically linked with the VM, then the JNI_OnLoad_
libname
function exported by the library is invoked. See the
JNI Specificationfor more details. Otherwise, the libname argument is loaded from a system library location and mapped to a native library image in an implementation-dependent manner.
First, if there is a security manager, its checkLink method is called with the libname as its argument. This may result in a security exception.
The method System.loadLibrary(String) is the conventional and convenient means of invoking this method. If native methods are to be used in the implementation of a class, a standard strategy is to put the native code in a library file (call it LibFile) and then to put a static initializer:
static { System.loadLibrary("LibFile"); }
within the class declaration. When the class is loaded and initialized, the necessary native code implementation for the native methods will then be loaded as well.
If this method is called more than once with the same library name, the second and subsequent calls are ignored.
libname - the name of the library.
SecurityException - if a security manager exists and its checkLink method doesn't allow loading of the specified dynamic library
UnsatisfiedLinkError - if either the libname argument contains a file path, the native library is not statically linked with the VM, or the library cannot be mapped to a native library image by the host system.
NullPointerException - if libname is null
Runtime.Version of the Java Runtime Environment
RetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4