Package Summary Overview Summary

Module jdk.incubator.foreign
Package jdk.incubator.foreign

# Class GroupLayout

java.lang.Object
jdk.incubator.foreign.GroupLayout

All Implemented Interfaces:
  `Constable`, `MemoryLayout`

public final class GroupLayout extends Object implements MemoryLayout
A group layout is used to combine multiple member layouts . There are two ways in which member layouts can be combined: if member layouts are laid out one after the other, the resulting group layout is said to be a struct (see `MemoryLayout.structLayout(MemoryLayout...)`); conversely, if all member layouts are laid out at the same starting offset, the resulting group layout is said to be a union (see `MemoryLayout.unionLayout(MemoryLayout...)`).

This is a value-based class; programmers should treat instances that are equal as interchangeable and should not use instances for synchronization, or unpredictable behavior may occur. For example, in a future release, synchronization may fail. The `equals` method should be used for comparisons.

Unless otherwise specified, passing a `null` argument, or an array argument containing one or more `null` elements to a method in this class causes a `NullPointerException` to be thrown.

Implementation Requirements:
  This class is immutable and thread-safe.

- ## Nested Class Summary

  ## Nested classes/interfaces declared in interface jdk.incubator.foreign.MemoryLayout

  `MemoryLayout.PathElement`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `final long`
  `bitAlignment()`
  Returns the alignment constraint associated with this layout, expressed in bits.
  `long`
  `bitSize()`
  Returns the layout size, in bits.
  `long`
  `byteSize()`
  Returns the layout size, in bytes.
  `Optional<DynamicConstantDesc<GroupLayout>>`
  `describeConstable()`
  Returns an `Optional` containing the nominal descriptor for this layout, if one can be constructed, or an empty `Optional` if one cannot be constructed.
  `boolean`
  `equals (Object other)`
  Indicates whether some other object is "equal to" this one.
  `int`
  `hashCode()`
  Returns a hash code value for the object.
  `boolean`
  `hasSize()`
  Returns `true` if this layout has a specified size.
  `boolean`
  `isPadding()`
  Returns true, if this layout is a padding layout.
  `boolean`
  `isStruct()`
  Returns `true`, if this group layout is a struct.
  `boolean`
  `isUnion()`
  Returns `true`, if this group layout is a union.
  `List<MemoryLayout>`
  `memberLayouts()`
  Returns the member layouts associated with this group.
  `final Optional<String>`
  `name()`
  Returns the name (if any) associated with this layout.
  `String`
  `toString()`
  Returns a string representation of the object.
  `GroupLayout`
  `withBitAlignment (long alignmentBits)`
  Creates a new layout which features the desired alignment constraint.
  `GroupLayout`
  `withName (String name)`
  Creates a new layout which features the desired layout name.

  ### Methods declared in class java.lang.Object

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

  ### Methods declared in interface jdk.incubator.foreign.MemoryLayout

  `bitAlignment, bitOffset, bitOffsetHandle, bitSize, byteAlignment, byteOffset, byteOffsetHandle, byteSize, hasSize, isPadding, map, name, select, sliceHandle, varHandle`

- ## Method Details

  - ### memberLayouts

    public List<MemoryLayout> memberLayouts()
    Returns the member layouts associated with this group.
    API Note:
      the order in which member layouts are returned is the same order in which member layouts have been passed to one of the group layout factory methods (see `MemoryLayout.structLayout(MemoryLayout...)`, `MemoryLayout.unionLayout(MemoryLayout...)`).
    Returns:
      the member layouts associated with this group.

  - ### toString

    public String toString()
    Description copied from class: `Object`
    Returns a string representation of the object.
    Specified by:
      `toString` in interface `MemoryLayout`
    Overrides:
      `toString` in class `Object`
    Returns:
      a string representation of the object.

  - ### isStruct

    public boolean isStruct()
    Returns `true`, if this group layout is a struct.
    Returns:
      `true`, if this group layout is a struct

  - ### isUnion

    public boolean isUnion()
    Returns `true`, if this group layout is a union.
    Returns:
      `true`, if this group layout is a union

  - ### equals

    public boolean equals (Object other)
    Description copied from class: `Object`
    Indicates whether some other object is "equal to" this one.

    The `equals` method implements an equivalence relation on non-null object references:

    - It is reflexive: for any non-null reference value `x`, `x.equals(x)` should return `true`.
    - It is symmetric: for any non-null reference values `x` and `y`, `x.equals(y)` should return `true` if and only if `y.equals(x)` returns `true`.
    - It is transitive: for any non-null reference values `x`, `y`, and `z`, if `x.equals(y)` returns `true` and `y.equals(z)` returns `true`, then `x.equals(z)` should return `true`.
    - It is consistent: for any non-null reference values `x` and `y`, multiple invocations of `x.equals(y)` consistently return `true` or consistently return `false`, provided no information used in `equals` comparisons on the objects is modified.
    - For any non-null reference value `x`, `x.equals(null)` should return `false`.

    An equivalence relation partitions the elements it operates on into equivalence classes ; all the members of an equivalence class are equal to each other. Members of an equivalence class are substitutable for each other, at least for some purposes.

    Specified by:
      `equals` in interface `MemoryLayout`
    Parameters:
      `other` - the reference object with which to compare.
    Returns:
      `true` if this object is the same as the obj argument; `false` otherwise.
    See Also:
      - `Object.hashCode()`
      - `HashMap`

  - ### hashCode

    public int hashCode()
    Description copied from class: `Object`
    Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by `HashMap`.

    The general contract of `hashCode` is:

    - Whenever it is invoked on the same object more than once during an execution of a Java application, the `hashCode` method must consistently return the same integer, provided no information used in `equals` comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
    - If two objects are equal according to the `equals` method, then calling the `hashCode` method on each of the two objects must produce the same integer result.
    - It is not required that if two objects are unequal according to the `equals` method, then calling the `hashCode` method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.
    Specified by:
      `hashCode` in interface `MemoryLayout`
    Returns:
      a hash code value for this object.
    See Also:
      - `Object.equals(java.lang.Object)`
      - `System.identityHashCode(java.lang.Object)`

  - ### describeConstable

    public Optional<DynamicConstantDesc<GroupLayout>> describeConstable()
    Description copied from interface: `MemoryLayout`
    Returns an `Optional` containing the nominal descriptor for this layout, if one can be constructed, or an empty `Optional` if one cannot be constructed.
    Specified by:
      `describeConstable` in interface `Constable`
    Specified by:
      `describeConstable` in interface `MemoryLayout`
    Returns:
      an `Optional` containing the nominal descriptor for this layout, if one can be constructed, or an empty `Optional` if one cannot be constructed

  - ### withName

    public GroupLayout withName (String name)
    Creates a new layout which features the desired layout name.
    Specified by:
      `withName` in interface `MemoryLayout`
    Parameters:
      `name` - the layout name.
    Returns:
      a new layout which is the same as this layout, except for the name associated with it.
    See Also:
      - `MemoryLayout.name()`

  - ### withBitAlignment

    public GroupLayout withBitAlignment (long alignmentBits)
    Creates a new layout which features the desired alignment constraint.
    Specified by:
      `withBitAlignment` in interface `MemoryLayout`
    Parameters:
      `alignmentBits` - the layout alignment constraint, expressed in bits.
    Returns:
      a new layout which is the same as this layout, except for the alignment constraint associated with it.

  - ### name

    public final Optional<String> name()
    Description copied from interface: `MemoryLayout`
    Returns the name (if any) associated with this layout.
    Specified by:
      `name` in interface `MemoryLayout`
    Returns:
      the name (if any) associated with this layout
    See Also:
      - `MemoryLayout.withName(String)`

  - ### bitAlignment

    public final long bitAlignment()
    Description copied from interface: `MemoryLayout`
    Returns the alignment constraint associated with this layout, expressed in bits. Layout alignment defines a power of two `A` which is the bit-wise alignment of the layout. If `A <= 8` then `A/8` is the number of bytes that must be aligned for any pointer that correctly points to this layout. Thus:
    - `A=8` means unaligned (in the usual sense), which is common in packets.
    - `A=64` means word aligned (on LP64), `A=32` int aligned, `A=16` short aligned, etc.
    - `A=512` is the most strict alignment required by the x86/SV ABI (for AVX-512 data).
    If no explicit alignment constraint was set on this layout (see `MemoryLayout.withBitAlignment(long)`), then this method returns the natural alignment constraint (in bits) associated with this layout.
    Specified by:
      `bitAlignment` in interface `MemoryLayout`
    Returns:
      the layout alignment constraint, in bits.

  - ### byteSize

    public long byteSize()
    Description copied from interface: `MemoryLayout`
    Returns the layout size, in bytes.
    Specified by:
      `byteSize` in interface `MemoryLayout`
    Returns:
      the layout size, in bytes

  - ### hasSize

    public boolean hasSize()
    Description copied from interface: `MemoryLayout`
    Returns `true` if this layout has a specified size. A layout does not have a specified size if it is (or contains) a sequence layout whose size is unspecified (see `SequenceLayout.elementCount()`). Value layouts (see `ValueLayout`) and padding layouts (see `MemoryLayout.paddingLayout(long)`) always have a specified size, therefore this method always returns `true` in these cases.
    Specified by:
      `hasSize` in interface `MemoryLayout`
    Returns:
      `true`, if this layout has a specified size.

  - ### bitSize

    public long bitSize()
    Description copied from interface: `MemoryLayout`
    Returns the layout size, in bits.
    Specified by:
      `bitSize` in interface `MemoryLayout`
    Returns:
      the layout size, in bits

  - ### isPadding

    public boolean isPadding()
    Description copied from interface: `MemoryLayout`
    Returns true, if this layout is a padding layout.
    Specified by:
      `isPadding` in interface `MemoryLayout`
    Returns:
      true, if this layout is a padding layout