Chapter 12
The java.lang Package

Process

Name

Process

Synopsis

Class Name:

java.lang.Process

Superclass:

java.lang.Object

Immediate Subclasses:

None that are provided on all platforms. However, a platform-specific version of Java should include at least one operating-system-specific subclass.

Interfaces Implemented:

None

Availability:

JDK 1.0 or later

Description

The Process class describes processes that are started by the exec() method in the Runtime class. A Process object controls a process and gets information about it.

The Process class is an abstract class; therefore, it cannot be instantiated. The actual Process objects created by the exec() method belong to operating-system-specific subclasses of Process that implement the Process methods in platform-dependent ways.

Note that losing all references to a Process object, thereby making it garbage collectable, does not result in the underlying Process object dying. It merely means that there is no longer a Java object to control the process. The process itself continues to run asynchronously. In addition, no guarantees are made as to whether a controlled process will be able to continue after its parent process dies.

Class Summary

public abstract class java.lang.Process extends java.lang.Object {
    // Constructors
    public Process();
    // Instance Methods
    public abstract void destroy();
    public abstract int exitValue();
    public abstract InputStream getErrorStream();
    public abstract InputStream getInputStream();
    public abstract OutputStream getOutputStream();
    public abstract int waitFor();
}

Constructors

Process

`public Process()`

Description: Creates a Process object.

Instance Methods

destroy

`abstract public void destroy()`

Description: This method kills the process controlled by this object.

exitValue

`abstract public int exitValue()`

Returns

The exit value of the process controlled by this object.

Throws

IllegalThreadStateException: If the process is still running and the exit value is not yet available.

Description

This method returns the exit value of the process that this object is controlling.

The waitFor() method is a similar method that waits for the controlled process to terminate and then returns its exit value.

getErrorStream

`abstract public InputStream getErrorStream()`

Returns

An InputStream object connected to the error stream of the process.

Description

This method returns an InputStream object that can read from the error stream of the process.

Although it is suggested that this InputStream not be buffered, the Java specification does not forbid such an implementation. In other words, although error output from programs is traditionally unbuffered, there is no guarantee that it won't be buffered. This means that error output written by the process may not be received immediately.

getInputStream

`abstract public InputStream getInputStream()`

Returns

An InputStream object that is connected to the standard output stream of the process.

Description

This method returns an InputStream object that can read from the standard output stream of the process.

This InputStream is likely to be buffered, which means that output written by the process may not be received immediately.

getOutputStream

`abstract public OutputStream getOutputStream()`

Returns

An OutputStream object that is connected to the standard input stream of the process.

Description

This method returns an OutputStream object that can write to the standard input stream of the process.

This OutputStream is likely to be buffered, which means that input sent to the process may not be received until the buffer fills up or a new line or carriage-return character is sent.

waitFor

`abstract public int waitFor()`

Returns

The exit value of the process controlled by this object.

Throws

InterruptedException: If another thread interrupts this thread while it is waiting for the process to exit.

Description

This method returns the exit value of the process that this object is controlling. If the process is still running, the method waits until the process terminates and its exit value is available.

The exitValue() method is a similar method that does not wait for the controlled process to terminate.

Inherited Methods

Method	Inherited From	Method	Inherited From
`clone()`	`Object`	`equals(Object)`	`Object`
`finalize()`	`Object`	`getClass()`	`Object`
`hashCode()`	`Object`	`notify()`	`Object`
`notifyAll()`	`Object`	`toString()`	`Object`
`wait()`	`Object`	`wait(long)`	`Object`
`wait(long, int)`	`Object`