Module java.base
Package java.lang.foreign

Interface ValueLayout

All Superinterfaces:
MemoryLayoutPREVIEW
All Known Subinterfaces:
ValueLayout.OfAddressPREVIEW, ValueLayout.OfBooleanPREVIEW, ValueLayout.OfBytePREVIEW, ValueLayout.OfCharPREVIEW, ValueLayout.OfDoublePREVIEW, ValueLayout.OfFloatPREVIEW, ValueLayout.OfIntPREVIEW, ValueLayout.OfLongPREVIEW, ValueLayout.OfShortPREVIEW
public sealed interface ValueLayout extends 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 region of memory 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.

Since:
19
Implementation Requirements:
implementing classes and subclasses are immutable, thread-safe and value-based.

  • Field Details

    • ADDRESS

      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, byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      MemoryLayout.valueLayout(MemorySegment.class, ByteOrder.nativeOrder());

    • JAVA_BYTE

      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());

    • JAVA_BOOLEAN

      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());

    • JAVA_CHAR

      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());

    • JAVA_SHORT

      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());

    • JAVA_INT

      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());

    • JAVA_LONG

      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());

    • JAVA_FLOAT

      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

      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());

    • ADDRESS_UNALIGNED

      static final ValueLayout.OfAddressPREVIEW ADDRESS_UNALIGNED
      An unaligned value layout constant whose size is the same as that of a machine address (size_t), and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      ADDRESS.withBitAlignment(8);
      API Note:
      Care should be taken when using unaligned value layouts as they may induce performance and portability issues.

    • JAVA_CHAR_UNALIGNED

      static final ValueLayout.OfCharPREVIEW JAVA_CHAR_UNALIGNED
      An unaligned value layout constant whose size is the same as that of a Java char and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      JAVA_CHAR.withBitAlignment(8);
      API Note:
      Care should be taken when using unaligned value layouts as they may induce performance and portability issues.

    • JAVA_SHORT_UNALIGNED

      static final ValueLayout.OfShortPREVIEW JAVA_SHORT_UNALIGNED
      An unaligned value layout constant whose size is the same as that of a Java short and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      JAVA_SHORT.withBitAlignment(8);
      API Note:
      Care should be taken when using unaligned value layouts as they may induce performance and portability issues.

    • JAVA_INT_UNALIGNED

      static final ValueLayout.OfIntPREVIEW JAVA_INT_UNALIGNED
      An unaligned value layout constant whose size is the same as that of a Java int and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      JAVA_INT.withBitAlignment(8);
      API Note:
      Care should be taken when using unaligned value layouts as they may induce performance and portability issues.

    • JAVA_LONG_UNALIGNED

      static final ValueLayout.OfLongPREVIEW JAVA_LONG_UNALIGNED
      An unaligned value layout constant whose size is the same as that of a Java long and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      JAVA_LONG.withBitAlignment(8);
      API Note:
      Care should be taken when using unaligned value layouts as they may induce performance and portability issues.

    • JAVA_FLOAT_UNALIGNED

      static final ValueLayout.OfFloatPREVIEW JAVA_FLOAT_UNALIGNED
      An unaligned value layout constant whose size is the same as that of a Java float and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      JAVA_FLOAT.withBitAlignment(8);
      API Note:
      Care should be taken when using unaligned value layouts as they may induce performance and portability issues.

    • JAVA_DOUBLE_UNALIGNED

      static final ValueLayout.OfDoublePREVIEW JAVA_DOUBLE_UNALIGNED
      An unaligned value layout constant whose size is the same as that of a Java double and byte order set to ByteOrder.nativeOrder(). Equivalent to the following code: 
      JAVA_DOUBLE.withBitAlignment(8);
      API Note:
      Care should be taken when using unaligned value layouts as they may induce performance and portability issues.

  • Method Details

    • order

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

    • withOrder

      ValueLayoutPREVIEW withOrder(ByteOrder order)
      Returns a value layout with the same carrier, alignment constraint 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.

    • arrayElementVarHandle

      VarHandle arrayElementVarHandle(int... shape)
      Creates a strided access var handle that can be used to access a memory segment as 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(
                                      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 accessed 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 access a memory segment as 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

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

    • withName

      ValueLayoutPREVIEW withName(String name)
      Returns a memory layout of the same type with the same size and alignment constraint 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

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