Java The Complete Reference, Seventh Edition

Runtime

TheRuntimeclass encapsulates the run-time environment. You cannot instantiate aRuntime

object. However, you can get a reference to the currentRuntimeobject by calling the static

methodRuntime.getRuntime( ). Once you obtain a reference to the currentRuntimeobject,

you can call several methods that control the state and behavior of the Java Virtual Machine.

Applets and other untrusted code typically cannot call any of theRuntimemethods without

raising aSecurityException. Commonly used methods defined byRuntimeare shown in

Table 16-11.

404 Part II: The Java Library

Method Description

void addShutdownHook(Threadthrd) Registersthrdas a thread to be run when the Java

Virtual Machine terminates.

Process exec(StringprogName)

throws IOException

Executes the program specified byprogNameas a

separate process. An object of typeProcessis

returned that describes the new process.

Process exec(StringprogName,

Stringenvironment[ ])

throws IOException

Executes the program specified byprogNameas a

separate process with the environment specified by

environment.An object of typeProcessis returned

that describes the new process.

Process exec(StringcomLineArray[ ])

throws IOException

Executes the command line specified by the strings in

comLineArrayas a separate process. An object of type

Processis returned that describes the new process.

Process exec(StringcomLineArray[ ],

Stringenvironment[ ])

throws IOException

Executes the command line specified by the strings

incomLineArrayas a separate process with the

environment specified byenvironment.An object of type

Processis returned that describes the new process.

void exit(intexitCode) Halts execution and returns the value ofexitCodeto

the parent process. By convention, 0 indicates normal

termination. All other values indicate some form of error.

long freeMemor y( ) Returns the approximate number of bytes of free

memor y available to the Java run-time system.

void gc( ) Initiates garbage collection.

static Runtime getRuntime( ) Returns the currentRuntimeobject.

void halt(intcode) Immediately terminates the Java Virtual Machine. No

termination threads or finalizers are run. The value of

codeis returned to the invoking process.

void load(Stringlibrar yFileName) Loads the dynamic librar y whose file is specified by

librar yFileName,which must specify its complete path.

void loadLibrar y(Stringlibrar yName) Loads the dynamic librar y whose name is associated

withlibrar yName.

TABLE 16-11 A Sampling of Methods Defined byRuntime