[Chapter 12] Process

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| 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` |  |

## See Also

`InterruptedException`, `Object`, `Runtime`

OutOfMemoryError |  | Runnable