Class ValueLayout

java.lang.Object
jdk.incubator.foreign.ValueLayout
All Implemented Interfaces:
Constable, MemoryLayout
Direct Known Subclasses:
ValueLayout.OfAddress, ValueLayout.OfBoolean, ValueLayout.OfByte, ValueLayout.OfChar, ValueLayout.OfDouble, ValueLayout.OfFloat, ValueLayout.OfInt, ValueLayout.OfLong, ValueLayout.OfShort

A value layout. A value layout is used to model the memory layout associated with values of basic data types, such as integral types (either signed or unsigned) and floating-point types. Each value layout has a size, an alignment (in bits), a byte order, and a carrier, that is, the Java type that should be used when accessing a memory region using the value layout.

This class defines useful value layout constants for Java primitive types and addresses. The layout constants in this class make implicit alignment and byte-ordering assumption: all layout constants in this class are byte-aligned, and their byte order is set to the platform default, thus making it easy to work with other APIs, such as arrays and ByteBuffer.

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.
  • Field Details

    • ADDRESS

      public static final ValueLayout.OfAddress ADDRESS
      A value layout constant whose size is the same as that of a machine address (size_t), bit alignment set to 8, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code:
      MemoryLayout.valueLayout(MemoryAddress.class, ByteOrder.nativeOrder()).withBitAlignment(8);
      
    • JAVA_BYTE

      public static final ValueLayout.OfByte JAVA_BYTE
      A value layout constant whose size is the same as that of a Java byte, bit alignment set to 8, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code:
      MemoryLayout.valueLayout(byte.class, ByteOrder.nativeOrder()).withBitAlignment(8);
      
    • JAVA_BOOLEAN

      public static final ValueLayout.OfBoolean JAVA_BOOLEAN
      A value layout constant whose size is the same as that of a Java boolean, bit alignment set to 8, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code:
      MemoryLayout.valueLayout(boolean.class, ByteOrder.nativeOrder()).withBitAlignment(8);
      
    • JAVA_CHAR

      public static final ValueLayout.OfChar JAVA_CHAR
      A value layout constant whose size is the same as that of a Java char, bit alignment set to 8, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code:
      MemoryLayout.valueLayout(char.class, ByteOrder.nativeOrder()).withBitAlignment(8);
      
    • JAVA_SHORT

      public static final ValueLayout.OfShort JAVA_SHORT
      A value layout constant whose size is the same as that of a Java short, bit alignment set to 8, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code:
      MemoryLayout.valueLayout(short.class, ByteOrder.nativeOrder()).withBitAlignment(8);
      
    • JAVA_INT

      public static final ValueLayout.OfInt JAVA_INT
      A value layout constant whose size is the same as that of a Java int, bit alignment set to 8, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code:
      MemoryLayout.valueLayout(int.class, ByteOrder.nativeOrder()).withBitAlignment(8);
      
    • JAVA_LONG

      public static final ValueLayout.OfLong JAVA_LONG
      A value layout constant whose size is the same as that of a Java long, bit alignment set to 8, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code:
      MemoryLayout.valueLayout(long.class, ByteOrder.nativeOrder()).withBitAlignment(8);
      
    • JAVA_FLOAT

      public static final ValueLayout.OfFloat JAVA_FLOAT
      A value layout constant whose size is the same as that of a Java float, bit alignment set to 8, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code:
      MemoryLayout.valueLayout(float.class, ByteOrder.nativeOrder()).withBitAlignment(8);
      
    • JAVA_DOUBLE

      public static final ValueLayout.OfDouble JAVA_DOUBLE
      A value layout constant whose size is the same as that of a Java double, bit alignment set to 8, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code:
      MemoryLayout.valueLayout(double.class, ByteOrder.nativeOrder()).withBitAlignment(8);
      
  • Method Details

    • order

      public ByteOrder order()
      Returns the value's byte order.
      Returns:
      the value's byte order
    • withOrder

      public ValueLayout withOrder(ByteOrder order)
      Returns a new value layout with given byte order.
      Parameters:
      order - the desired byte order.
      Returns:
      a new value layout with given byte order.
    • 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.
    • 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:
    • carrier

      public Class<?> carrier()
      Returns the carrier associated with this value layout.
      Returns:
      the carrier associated with this value layout
    • 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:
    • describeConstable

      public Optional<DynamicConstantDesc<ValueLayout>> 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 ValueLayout 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:
    • withBitAlignment

      public ValueLayout 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:
    • 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