# Class ModuleDescriptor

java.lang.Object
java.lang.module.ModuleDescriptor

All Implemented Interfaces:
  `Comparable<ModuleDescriptor>`

public final class ModuleDescriptor extends Object implements Comparable<ModuleDescriptor>
A module descriptor.

A module descriptor describes a named module and defines methods to obtain each of its components. The module descriptor for a named module in the Java virtual machine is obtained by invoking the `Module`'s `getDescriptor` method. Module descriptors can also be created using the `ModuleDescriptor.Builder` class or by reading the binary form of a module declaration (`module-info.class`) using the `read` methods defined here.

A module descriptor describes a normal, open, or automatic module. Normal modules and open modules describe their dependences, `exported-packages`, the services that they use or provide, and other components. Normal modules may open specific packages. The module descriptor for an open module does not declare any open packages (its `opens` method returns an empty set) but when instantiated in the Java virtual machine then it is treated as if all packages are open. The module descriptor for an automatic module does not declare any dependences (except for the mandatory dependency on `java.base`), and does not declare any exported or open packages. Automatic modules receive special treatment during resolution so that they read all other modules in the configuration. When an automatic module is instantiated in the Java virtual machine then it reads every unnamed module and is treated as if all packages are exported and open.

`ModuleDescriptor` objects are immutable and safe for use by multiple concurrent threads.

Since:
  9
See Also:
  - `Module`

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `static final class`
  `ModuleDescriptor.Builder`
  A builder for building `ModuleDescriptor` objects.
  `static final class`
  `ModuleDescriptor.Exports`
  A package exported by a module, may be qualified or unqualified.
  `static enum`
  `ModuleDescriptor.Modifier`
  A modifier on a module.
  `static final class`
  `ModuleDescriptor.Opens`
  A package opened by a module, may be qualified or unqualified.
  `static final class`
  `ModuleDescriptor.Provides`
  A service that a module provides one or more implementations of.
  `static final class`
  `ModuleDescriptor.Requires`
  A dependence upon a module.
  `static final class`
  `ModuleDescriptor.Version`
  A module's version string.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `Set<AccessFlag>`
  `accessFlags()`
  Returns the set of the module flags.
  `int`
  `compareTo(ModuleDescriptor that)`
  Compares this module descriptor to another.
  `boolean`
  `equals(Object ob)`
  Tests this module descriptor for equality with the given object.
  `Set<ModuleDescriptor.Exports>`
  `exports()`
  Returns the set of `Exports` objects representing the exported packages.
  `int`
  `hashCode()`
  Computes a hash code for this module descriptor.
  `boolean`
  `isAutomatic()`
  Returns `true` if this is an automatic module.
  `boolean`
  `isOpen()`
  Returns `true` if this is an open module.
  `Optional<String>`
  `mainClass()`
  Returns the module main class.
  `Set<ModuleDescriptor.Modifier>`
  `modifiers()`
  Returns the set of module modifiers.
  `String`
  `name()`
  Returns the module name.
  `static ModuleDescriptor.Builder`
  `newAutomaticModule(String name)`
  Instantiates a builder to build a module descriptor for an automatic module.
  `static ModuleDescriptor.Builder`
  `newModule(String name)`
  Instantiates a builder to build a module descriptor for a normal module.
  `static ModuleDescriptor.Builder`
  `newModule(String name, Set<ModuleDescriptor.Modifier> ms)`
  Instantiates a builder to build a module descriptor.
  `static ModuleDescriptor.Builder`
  `newOpenModule(String name)`
  Instantiates a builder to build a module descriptor for an open module.
  `Set<ModuleDescriptor.Opens>`
  `opens()`
  Returns the set of `Opens` objects representing the open packages.
  `Set<String>`
  `packages()`
  Returns the set of packages in the module.
  `Set<ModuleDescriptor.Provides>`
  `provides()`
  Returns the set of `Provides` objects representing the services that the module provides.
  `Optional<String>`
  `rawVersion()`
  Returns the string with the possibly-unparseable version of the module.
  `static ModuleDescriptor`
  `read(InputStream in)`
  Reads the binary form of a module declaration from an input stream as a module descriptor.
  `static ModuleDescriptor`
  `read(InputStream in, Supplier<Set<String>> packageFinder)`
  Reads the binary form of a module declaration from an input stream as a module descriptor.
  `static ModuleDescriptor`
  `read(ByteBuffer bb)`
  Reads the binary form of a module declaration from a byte buffer as a module descriptor.
  `static ModuleDescriptor`
  `read(ByteBuffer bb, Supplier<Set<String>> packageFinder)`
  Reads the binary form of a module declaration from a byte buffer as a module descriptor.
  `Set<ModuleDescriptor.Requires>`
  `requires()`
  Returns the set of `Requires` objects representing the module dependences.
  `String`
  `toNameAndVersion()`
  Returns a string containing the module name and, if present, its version.
  `String`
  `toString()`
  Returns a string describing the module.
  `Set<String>`
  `uses()`
  Returns the set of service dependences.
  `Optional<ModuleDescriptor.Version>`
  `version()`
  Returns the module version.

  ### Methods declared in class Object

  `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- ## Method Details

  - ### name

    public String name()

    Returns the module name.

    Returns:
      The module name

  - ### modifiers

    public Set<ModuleDescriptor.Modifier> modifiers()

    Returns the set of module modifiers.

    Returns:
      A possibly-empty unmodifiable set of modifiers

  - ### accessFlags

    public Set<AccessFlag> accessFlags()
    Returns the set of the module flags.
    Returns:
      A possibly-empty unmodifiable set of module flags
    See Java Virtual Machine Specification:
      4.7.25 The Module Attribute
    Since:
      20
    See Also:
      - `modifiers()`

  - ### isOpen

    public boolean isOpen()

    Returns `true` if this is an open module.

    This method is equivalent to testing if the set of `modifiers` contains the `OPEN` modifier.

    Returns:
      `true` if this is an open module

  - ### isAutomatic

    public boolean isAutomatic()

    Returns `true` if this is an automatic module.

    This method is equivalent to testing if the set of `modifiers` contains the `AUTOMATIC` modifier.

    Returns:
      `true` if this is an automatic module

  - ### requires

    public Set<ModuleDescriptor.Requires> requires()

    Returns the set of `Requires` objects representing the module dependences.

    The set includes a dependency on "`java.base`" when this module is not named "`java.base`". If this module is an automatic module then it does not have a dependency on any module other than "`java.base`".

    Returns:
      A possibly-empty unmodifiable set of `ModuleDescriptor.Requires` objects

  - ### exports

    public Set<ModuleDescriptor.Exports> exports()

    Returns the set of `Exports` objects representing the exported packages.

    If this module is an automatic module then the set of exports is empty.

    Returns:
      A possibly-empty unmodifiable set of exported packages

  - ### opens

    public Set<ModuleDescriptor.Opens> opens()

    Returns the set of `Opens` objects representing the open packages.

    If this module is an open module or an automatic module then the set of open packages is empty.

    Returns:
      A possibly-empty unmodifiable set of open packages

  - ### uses

    public Set<String> uses()

    Returns the set of service dependences.

    If this module is an automatic module then the set of service dependences is empty.

    Returns:
      A possibly-empty unmodifiable set of the binary names of the service types used

  - ### provides

    public Set<ModuleDescriptor.Provides> provides()

    Returns the set of `Provides` objects representing the services that the module provides.

    Returns:
      The possibly-empty unmodifiable set of the services that this module provides

  - ### version

    public Optional<ModuleDescriptor.Version> version()

    Returns the module version.

    Returns:
      This module's version, or an empty `Optional` if the module does not have a version or the version is unparseable

  - ### rawVersion

    public Optional<String> rawVersion()

    Returns the string with the possibly-unparseable version of the module.

    Returns:
      The string containing the version of the module or an empty `Optional` if the module does not have a version
    See Also:
      - `version()`

  - ### toNameAndVersion

    public String toNameAndVersion()

    Returns a string containing the module name and, if present, its version.

    Returns:
      A string containing the module name and, if present, its version

  - ### mainClass

    public Optional<String> mainClass()

    Returns the module main class.

    Returns:
      The binary name of the module's main class

  - ### packages

    public Set<String> packages()
    Returns the set of packages in the module.

    The set of packages includes all exported and open packages, as well as the packages of any service providers, and the package for the main class.

    Returns:
      A possibly-empty unmodifiable set of the packages in the module

  - ### compareTo

    public int compareTo(ModuleDescriptor that)
    Compares this module descriptor to another.

    Two `ModuleDescriptor` objects are compared by comparing their module names lexicographically. Where the module names are equal then the module versions are compared. When comparing the module versions then a module descriptor with a version is considered to succeed a module descriptor that does not have a version. If both versions are unparseable then the raw version strings are compared lexicographically. Where the module names are equal and the versions are equal (or not present in both), then the set of modifiers are compared. Sets of modifiers are compared by comparing a binary value computed for each set. If a modifier is present in the set then the bit at the position of its ordinal is `1` in the binary value, otherwise `0`. If the two set of modifiers are also equal then the other components of the module descriptors are compared in a manner that is consistent with `equals`.

    Specified by:
      `compareTo` in interface `Comparable<ModuleDescriptor>`
    Parameters:
      `that` - The module descriptor to compare
    Returns:
      A negative integer, zero, or a positive integer if this module descriptor is less than, equal to, or greater than the given module descriptor

  - ### equals

    public boolean equals(Object ob)
    Tests this module descriptor for equality with the given object.

    If the given object is not a `ModuleDescriptor` then this method returns `false`. Two module descriptors are equal if each of their corresponding components is equal.

    This method satisfies the general contract of the `Object.equals` method.

    Overrides:
      `equals` in class `Object`
    Parameters:
      `ob` - the object to which this object is to be compared
    Returns:
      `true` if, and only if, the given object is a module descriptor that is equal to this module descriptor
    See Also:
      - `Object.hashCode()`
      - `HashMap`

  - ### hashCode

    public int hashCode()
    Computes a hash code for this module descriptor.

    The hash code is based upon the components of the module descriptor, and satisfies the general contract of the `Object.hashCode` method.

    Overrides:
      `hashCode` in class `Object`
    Returns:
      The hash-code value for this module descriptor
    See Also:
      - `Object.equals(java.lang.Object)`
      - `System.identityHashCode(Object)`

  - ### toString

    public String toString()

    Returns a string describing the module.

    Overrides:
      `toString` in class `Object`
    Returns:
      A string describing the module

  - ### newModule

    public static ModuleDescriptor.Builder newModule(String name, Set<ModuleDescriptor.Modifier> ms)
    Instantiates a builder to build a module descriptor.
    Parameters:
      `name` - The module name
      `ms` - The set of module modifiers
    Returns:
      A new builder
    Throws:
      `IllegalArgumentException` - If the module name is `null` or is not a legal module name, or the set of modifiers contains `AUTOMATIC` with other modifiers

  - ### newModule

    public static ModuleDescriptor.Builder newModule(String name)
    Instantiates a builder to build a module descriptor for a normal module. This method is equivalent to invoking `newModule` with an empty set of `modifiers`.
    Parameters:
      `name` - The module name
    Returns:
      A new builder
    Throws:
      `IllegalArgumentException` - If the module name is `null` or is not a legal module name

  - ### newOpenModule

    public static ModuleDescriptor.Builder newOpenModule(String name)
    Instantiates a builder to build a module descriptor for an open module. This method is equivalent to invoking `newModule` with the `OPEN` modifier.

    The builder for an open module cannot be used to declare any open packages.

    Parameters:
      `name` - The module name
    Returns:
      A new builder that builds an open module
    Throws:
      `IllegalArgumentException` - If the module name is `null` or is not a legal module name

  - ### newAutomaticModule

    public static ModuleDescriptor.Builder newAutomaticModule(String name)
    Instantiates a builder to build a module descriptor for an automatic module. This method is equivalent to invoking `newModule` with the `AUTOMATIC` modifier.

    The builder for an automatic module cannot be used to declare module or service dependences. It also cannot be used to declare any exported or open packages.

    Parameters:
      `name` - The module name
    Returns:
      A new builder that builds an automatic module
    Throws:
      `IllegalArgumentException` - If the module name is `null` or is not a legal module name
    See Also:
      - `ModuleFinder.of(Path[])`

  - ### read

    public static ModuleDescriptor read(InputStream in, Supplier<Set<String>> packageFinder) throws IOException
    Reads the binary form of a module declaration from an input stream as a module descriptor.

    If the descriptor encoded in the input stream does not indicate a set of packages in the module then the `packageFinder` will be invoked. The set of packages that the `packageFinder` returns must include all the packages that the module exports, opens, as well as the packages of the service implementations that the module provides, and the package of the main class (if the module has a main class). If the `packageFinder` throws an `UncheckedIOException` then `IOException` cause will be re-thrown.

    If there are bytes following the module descriptor then it is implementation specific as to whether those bytes are read, ignored, or reported as an `InvalidModuleDescriptorException`. If this method fails with an `InvalidModuleDescriptorException` or `IOException` then it may do so after some, but not all, bytes have been read from the input stream. It is strongly recommended that the stream be promptly closed and discarded if an exception occurs.

    API Note:
      The `packageFinder` parameter is for use when reading module descriptors from legacy module-artifact formats that do not record the set of packages in the descriptor itself.
    Parameters:
      `in` - The input stream
      `packageFinder` - A supplier that can produce the set of packages
    Returns:
      The module descriptor
    Throws:
      `InvalidModuleDescriptorException` - If an invalid module descriptor is detected or the set of packages returned by the `packageFinder` does not include all of the packages obtained from the module descriptor
      `IOException` - If an I/O error occurs reading from the input stream or `UncheckedIOException` is thrown by the package finder

  - ### read

    public static ModuleDescriptor read(InputStream in) throws IOException
    Reads the binary form of a module declaration from an input stream as a module descriptor. This method works exactly as specified by the 2-arg `read` method with the exception that a package finder is not used to find additional packages when the module descriptor read from the stream does not indicate the set of packages.
    Parameters:
      `in` - The input stream
    Returns:
      The module descriptor
    Throws:
      `InvalidModuleDescriptorException` - If an invalid module descriptor is detected
      `IOException` - If an I/O error occurs reading from the input stream

  - ### read

    public static ModuleDescriptor read(ByteBuffer bb, Supplier<Set<String>> packageFinder)
    Reads the binary form of a module declaration from a byte buffer as a module descriptor.

    If the descriptor encoded in the byte buffer does not indicate a set of packages in the module then the `packageFinder` will be invoked. The set of packages that the `packageFinder` returns must include all the packages that the module exports, opens, as well as the packages of the service implementations that the module provides, and the package of the main class (if the module has a main class). If the `packageFinder` throws an `UncheckedIOException` then `IOException` cause will be re-thrown.

    The module descriptor is read from the buffer starting at index `p`, where `p` is the buffer's `position` when this method is invoked. Upon return the buffer's position will be equal to `p + n` where `n` is the number of bytes read from the buffer.

    If there are bytes following the module descriptor then it is implementation specific as to whether those bytes are read, ignored, or reported as an `InvalidModuleDescriptorException`. If this method fails with an `InvalidModuleDescriptorException` then it may do so after some, but not all, bytes have been read.

    API Note:
      The `packageFinder` parameter is for use when reading module descriptors from legacy module-artifact formats that do not record the set of packages in the descriptor itself.
    Parameters:
      `bb` - The byte buffer
      `packageFinder` - A supplier that can produce the set of packages
    Returns:
      The module descriptor
    Throws:
      `InvalidModuleDescriptorException` - If an invalid module descriptor is detected or the set of packages returned by the `packageFinder` does not include all of the packages obtained from the module descriptor

  - ### read

    public static ModuleDescriptor read(ByteBuffer bb)
    Reads the binary form of a module declaration from a byte buffer as a module descriptor. This method works exactly as specified by the 2-arg `read` method with the exception that a package finder is not used to find additional packages when the module descriptor encoded in the buffer does not indicate the set of packages.
    Parameters:
      `bb` - The byte buffer
    Returns:
      The module descriptor
    Throws:
      `InvalidModuleDescriptorException` - If an invalid module descriptor is detected