Module java.base
Package java.lang.foreign

Class ValueLayout

java.lang.Object
java.lang.foreign.ValueLayout
All Implemented Interfaces:
MemoryLayoutPREVIEW
Direct Known Subclasses:
ValueLayout.OfAddressPREVIEW, ValueLayout.OfBooleanPREVIEW, ValueLayout.OfBytePREVIEW, ValueLayout.OfCharPREVIEW, ValueLayout.OfDoublePREVIEW, ValueLayout.OfFloatPREVIEW, ValueLayout.OfIntPREVIEW, ValueLayout.OfLongPREVIEW, ValueLayout.OfShortPREVIEW
public sealed class ValueLayout extends Object implements MemoryLayoutPREVIEW permits ValueLayout.OfBytePREVIEW, ValueLayout.OfShortPREVIEW, ValueLayout.OfCharPREVIEW, ValueLayout.OfIntPREVIEW, ValueLayout.OfFloatPREVIEW, ValueLayout.OfLongPREVIEW, ValueLayout.OfDoublePREVIEW, ValueLayout.OfBooleanPREVIEW, ValueLayout.OfAddressPREVIEW
ValueLayout is a preview API of the Java platform.
Programs can only use ValueLayout when preview features are enabled.
Preview features may be removed in a future release, or upgraded to permanent features of the Java platform.
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 accessingPREVIEW 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.

Implementation Requirements:
This class and its subclasses are immutable, thread-safe and value-based.
Since:
19

  • Field Details

    • ADDRESS

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

    • JAVA_BYTE

      public static final ValueLayout.OfBytePREVIEW 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.OfBooleanPREVIEW 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.OfCharPREVIEW JAVA_CHAR
      A value layout constant whose size is the same as that of a Java char, bit alignment set to 16, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      MemoryLayout.valueLayout(char.class, ByteOrder.nativeOrder()).withBitAlignment(16);

    • JAVA_SHORT

      public static final ValueLayout.OfShortPREVIEW JAVA_SHORT
      A value layout constant whose size is the same as that of a Java short, bit alignment set to 16, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      MemoryLayout.valueLayout(short.class, ByteOrder.nativeOrder()).withBitAlignment(16);

    • JAVA_INT

      public static final ValueLayout.OfIntPREVIEW JAVA_INT
      A value layout constant whose size is the same as that of a Java int, bit alignment set to 32, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      MemoryLayout.valueLayout(int.class, ByteOrder.nativeOrder()).withBitAlignment(32);

    • JAVA_LONG

      public static final ValueLayout.OfLongPREVIEW JAVA_LONG
      A value layout constant whose size is the same as that of a Java long, bit alignment set to 64, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      MemoryLayout.valueLayout(long.class, ByteOrder.nativeOrder()).withBitAlignment(64);

    • JAVA_FLOAT

      public static final ValueLayout.OfFloatPREVIEW JAVA_FLOAT
      A value layout constant whose size is the same as that of a Java float, bit alignment set to 32, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      MemoryLayout.valueLayout(float.class, ByteOrder.nativeOrder()).withBitAlignment(32);

    • JAVA_DOUBLE

      public static final ValueLayout.OfDoublePREVIEW JAVA_DOUBLE
      A value layout constant whose size is the same as that of a Java double, bit alignment set to 64, and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      MemoryLayout.valueLayout(double.class, ByteOrder.nativeOrder()).withBitAlignment(64);

  • Method Details

    • order

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

    • withOrder

      public ValueLayoutPREVIEW withOrder(ByteOrder order)
      Returns a value layout with the same carrier, alignment constraints and name as this value layout, but with the specified byte order.
      Parameters:
      order - the desired byte order.
      Returns:
      a value layout with the given byte order.

    • toString

      public String toString()
      Returns the string representation of this layout.
      Specified by:
      toString in interface MemoryLayoutPREVIEW
      Returns:
      the string representation of this layout

    • equals

      public boolean equals(Object other)
      Compares the specified object with this layout for equality. Returns true if and only if the specified object is also a layout, and it is equal to this layout. Two layouts are considered equal if they are of the same kind, have the same size, name and alignment constraints. Furthermore, depending on the layout kind, additional conditions must be satisfied:
      Specified by:
      equals in interface MemoryLayoutPREVIEW
      Parameters:
      other - the object to be compared for equality with this layout.
      Returns:
      true if the specified object is equal to this layout.
      See Also:

    • arrayElementVarHandle

      public VarHandle arrayElementVarHandle(int... shape)
      Creates a strided access var handle that can be used to dereference a multi-dimensional array. The layout of this array is a sequence layout with shape.length nested sequence layouts. The element layout of the sequence layout at depth shape.length is this value layout. As a result, if shape.length == 0, the array layout will feature only one dimension.

      The resulting var handle will feature sizes.length + 1 coordinates of type long, which are used as indices into a multi-dimensional array.

      For instance, the following method call: 

      VarHandle arrayHandle = ValueLayout.JAVA_INT.arrayElementVarHandle(10, 20);
      Can be used to access a multi-dimensional array whose layout is as follows: 
      SequenceLayout arrayLayout = MemoryLayout.sequenceLayout(-1,
                                     MemoryLayout.sequenceLayout(10,
                                                 MemoryLayout.sequenceLayout(20, ValueLayout.JAVA_INT)));
      The resulting var handle arrayHandle will feature 3 coordinates of type long; each coordinate is interpreted as an index into the corresponding sequence layout. If we refer to the var handle coordinates, from left to right, as x, y and z respectively, the final offset dereferenced by the var handle can be computed with the following formula: 
      
 offset = (10 * 20 * 4 * x) + (20 * 4 * y) + (4 * z)
      Additionally, the values of x, y and z are constrained as follows:
      • 0 <= x < arrayLayout.elementCount()
      • 0 <= y < 10
      • 0 <= z < 20

      Consider the following access expressions: 

      int value1 = arrayHandle.get(10, 2, 4); // ok, accessed offset = 8176
int value2 = arrayHandle.get(0, 0, 30); // out of bounds value for z
      In the first case, access is well-formed, as the values for x, y and z conform to the bounds specified above. In the second case, access fails with IndexOutOfBoundsException, as the value for z is outside its specified bounds.
      Parameters:
      shape - the size of each nested array dimension.
      Returns:
      a var handle which can be used to dereference a multi-dimensional array, featuring shape.length + 1 long coordinates.
      Throws:
      IllegalArgumentException - if shape[i] < 0, for at least one index i.
      UnsupportedOperationException - if bitAlignment() > bitSize().
      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()
      Returns the hash code value for this layout.
      Specified by:
      hashCode in interface MemoryLayoutPREVIEW
      Returns:
      the hash code value for this layout
      See Also:

    • withName

      public ValueLayoutPREVIEW withName(String name)
      Returns a memory layout with the same size and alignment constraints as this layout, but with the specified name.
      Specified by:
      withName in interface MemoryLayoutPREVIEW
      Parameters:
      name - the layout name.
      Returns:
      a memory layout with the given name.
      See Also:

    • withBitAlignment

      public ValueLayoutPREVIEW withBitAlignment(long alignmentBits)
      Returns a memory layout with the same size and name as this layout, but with the specified alignment constraints (in bits).
      Specified by:
      withBitAlignment in interface MemoryLayoutPREVIEW
      Parameters:
      alignmentBits - the layout alignment constraint, expressed in bits.
      Returns:
      a memory layout with the given alignment constraints.

    • 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 MemoryLayoutPREVIEW
      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)PREVIEW), then this method returns the natural alignment constraint (in bits) associated with this layout.
      Specified by:
      bitAlignment in interface MemoryLayoutPREVIEW
      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 MemoryLayoutPREVIEW
      Returns:
      the layout size, in bytes

    • bitSize

      public long bitSize()
      Description copied from interface: MemoryLayout
      Returns the layout size, in bits.
      Specified by:
      bitSize in interface MemoryLayoutPREVIEW
      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 MemoryLayoutPREVIEW
      Returns:
      true, if this layout is a padding layout