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
A group layout is used to combine together 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.ofStruct(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.ofUnion(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.

  • 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.ofStruct(MemoryLayout...), MemoryLayout.ofUnion(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. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

      The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of: 

       getClass().getName() + '@' + Integer.toHexString(hashCode())
      Specified by:
      toString in interface MemoryLayout
      Overrides:
      toString in class Object
      Returns:
      a string representation of the object.

    • isStruct

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

    • isUnion

      public boolean isUnion()
      Is this group layout 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.

      The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

      Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

      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(Object) 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 Object.equals(java.lang.Object) 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.
      Returns:
      An Optional containing the resulting nominal descriptor, 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.

      This is equivalent to the following code: 

      
    withAttribute(LAYOUT_NAME, 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 to 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 to it.

    • withAttribute

      public GroupLayout withAttribute​(String name, Constable value)
      Returns a new memory layout which features the same attributes as this layout, plus the newly specified attribute. If this layout already contains an attribute with the same name, the existing attribute value is overwritten in the returned layout.
      Specified by:
      withAttribute in interface MemoryLayout
      Parameters:
      name - the attribute name.
      value - the attribute value.
      Returns:
      a new memory layout which features the same attributes as this layout, plus the newly specified attribute.

    • name

      public final Optional<String> name()
      Description copied from interface: MemoryLayout
      Return the name (if any) associated with this layout.

      This is equivalent to the following code: 

      
    attribute(LAYOUT_NAME).map(String.class::cast);
      Specified by:
      name in interface MemoryLayout
      Returns:
      the layout name (if any).
      See Also:
      MemoryLayout.withName(String)

    • attribute

      public Optional<Constable> attribute​(String name)
      Description copied from interface: MemoryLayout
      Returns the attribute with the given name (if it exists).
      Specified by:
      attribute in interface MemoryLayout
      Parameters:
      name - the attribute name
      Returns:
      the attribute with the given name (if it exists).

    • attributes

      public Stream<String> attributes()
      Description copied from interface: MemoryLayout
      Returns a stream of the attribute names associated with this layout.
      Specified by:
      attributes in interface MemoryLayout
      Returns:
      a stream of the attribute names associated with this layout.

    • 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.

    • hasSize

      public boolean hasSize()
      Description copied from interface: MemoryLayout
      Does this layout have 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.ofPaddingBits(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
      Computes 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
      Is this a padding layout (e.g. a layout created from MemoryLayout.ofPaddingBits(long)) ?
      Specified by:
      isPadding in interface MemoryLayout
      Returns:
      true, if this layout is a padding layout.