Module java.base
Package java.lang.foreign

Interface ValueLayout

All Superinterfaces:
MemoryLayout
All Known Subinterfaces:
AddressLayout, ValueLayout.OfBoolean, ValueLayout.OfByte, ValueLayout.OfChar, ValueLayout.OfDouble, ValueLayout.OfFloat, ValueLayout.OfInt, ValueLayout.OfLong, ValueLayout.OfShort
public sealed interface ValueLayout extends MemoryLayout permits ValueLayout.OfBoolean, ValueLayout.OfByte, ValueLayout.OfChar, ValueLayout.OfShort, ValueLayout.OfInt, ValueLayout.OfFloat, ValueLayout.OfLong, ValueLayout.OfDouble, AddressLayout
A layout that models values of basic data types. Examples of values modelled by a value layout are integral values (either signed or unsigned), floating-point values and address values.

Each value layout has a size, an alignment (both expressed in bytes), a byte order, and a carrier, that is, the Java type that should be used when accessing a region of memory using the value layout.

This class defines useful value layout constants for Java primitive types and addresses.

Since:
22
API Note:
Some characteristics of the Java layout constants are platform-dependent. For instance, the byte order of these constants is set to the native byte order, thus making it easy to work with other APIs, such as arrays and ByteBuffer. Moreover, the alignment constraint of JAVA_LONG and JAVA_DOUBLE is set to 8 bytes on 64-bit platforms, but only to 4 bytes on 32-bit platforms.
Implementation Requirements:
implementing classes and subclasses are immutable, thread-safe and value-based.
Sealed Graph:

  • Field Details

    • ADDRESS

      static final AddressLayout ADDRESS
      An address layout constant whose size is the same as that of a machine address (size_t), byte alignment set to sizeof(size_t), byte order set to ByteOrder.nativeOrder().

    • JAVA_BYTE

      static final ValueLayout.OfByte JAVA_BYTE
      A value layout constant whose size is the same as that of a Java byte, byte alignment set to 1, and byte order set to ByteOrder.nativeOrder().

    • JAVA_BOOLEAN

      static final ValueLayout.OfBoolean JAVA_BOOLEAN
      A value layout constant whose size is the same as that of a Java boolean, byte alignment set to 1, and byte order set to ByteOrder.nativeOrder().

    • JAVA_CHAR

      static final ValueLayout.OfChar JAVA_CHAR
      A value layout constant whose size is the same as that of a Java char, byte alignment set to 2, and byte order set to ByteOrder.nativeOrder().

    • JAVA_SHORT

      static final ValueLayout.OfShort JAVA_SHORT
      A value layout constant whose size is the same as that of a Java short, byte alignment set to 2, and byte order set to ByteOrder.nativeOrder().

    • JAVA_INT

      static final ValueLayout.OfInt JAVA_INT
      A value layout constant whose size is the same as that of a Java int, byte alignment set to 4, and byte order set to ByteOrder.nativeOrder().

    • JAVA_LONG

      static final ValueLayout.OfLong JAVA_LONG
      A value layout constant whose size is the same as that of a Java long, (platform-dependent) byte alignment set to ADDRESS.byteSize(), and byte order set to ByteOrder.nativeOrder().

    • JAVA_FLOAT

      static final ValueLayout.OfFloat JAVA_FLOAT
      A value layout constant whose size is the same as that of a Java float, byte alignment set to 4, and byte order set to ByteOrder.nativeOrder().

    • JAVA_DOUBLE

      static final ValueLayout.OfDouble JAVA_DOUBLE
      A value layout constant whose size is the same as that of a Java double, (platform-dependent) byte alignment set to ADDRESS.byteSize(), and byte order set to ByteOrder.nativeOrder().

    • ADDRESS_UNALIGNED

      static final AddressLayout ADDRESS_UNALIGNED
      An unaligned address 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.withByteAlignment(1);
      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.OfChar 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.withByteAlignment(1);
      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.OfShort 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.withByteAlignment(1);
      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.OfInt 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.withByteAlignment(1);
      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.OfLong 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.withByteAlignment(1);
      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.OfFloat 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.withByteAlignment(1);
      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.OfDouble 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.withByteAlignment(1);
      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

      ValueLayout withOrder(ByteOrder order)
      Returns a value layout with the same characteristics as this layout, but with the given byte order.
      Parameters:
      order - the desired byte order.
      Returns:
      a value layout with the same characteristics as this layout, but with the given byte order

    • withoutName

      ValueLayout withoutName()
      Returns a memory layout with the same characteristics as this layout, but with no name.
      Specified by:
      withoutName in interface MemoryLayout
      Returns:
      a memory layout with the same characteristics as this layout, but with no name
      See Also:

    • carrier

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

    • withName

      ValueLayout withName(String name)
      Returns a memory layout with the same characteristics as this layout, but with the given name.
      Specified by:
      withName in interface MemoryLayout
      Parameters:
      name - the layout name.
      Returns:
      a memory layout with the same characteristics as this layout, but with the given name
      See Also:

    • withByteAlignment

      ValueLayout withByteAlignment(long byteAlignment)
      Returns a memory layout with the same characteristics as this layout, but with the given alignment constraint (in bytes).
      Specified by:
      withByteAlignment in interface MemoryLayout
      Parameters:
      byteAlignment - the layout alignment constraint, expressed in bytes.
      Returns:
      a memory layout with the same characteristics as this layout, but with the given alignment constraint (in bytes)
      Throws:
      IllegalArgumentException - if byteAlignment is not a power of two.

    • varHandle

      VarHandle varHandle()
      Returns a var handle which can be used to access values described by this value layout, in a given memory segment..

      The returned var handle's var type is the carrier type of this value layout, and the list of coordinate types is (MemorySegment, long), where the memory segment coordinate corresponds to the memory segment to be accessed, and the long coordinate corresponds to the byte offset into the accessed memory segment at which the access occurs.

      The returned var handle checks that accesses are aligned according to this value layout's alignment constraint.

      Returns:
      a var handle which can be used to access values described by this value layout, in a given memory segment.
      See Also:
      API Note:
      This method is similar, but more efficient, than calling MemoryLayout#varHandle(PathElement...) with an empty path element array, as it avoids the creation of the var args array., The returned var handle features certain access mode restrictions common to all memory access var handles derived from memory layouts.