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Showing content from https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/foreign/ValueLayout.html below:

ValueLayout (Java SE 21 & JDK 21)

All Superinterfaces:: MemoryLayout^PREVIEW

All Known Subinterfaces:: AddressLayout^PREVIEW, ValueLayout.OfBoolean^PREVIEW, ValueLayout.OfByte^PREVIEW, ValueLayout.OfChar^PREVIEW, ValueLayout.OfDouble^PREVIEW, ValueLayout.OfFloat^PREVIEW, ValueLayout.OfInt^PREVIEW, ValueLayout.OfLong^PREVIEW, ValueLayout.OfShort^PREVIEW

ValueLayout is a preview API of the Java platform.

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^PREVIEW a region of memory using the value layout.

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

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 Class Hierarchy Graph:
Since:: 19

Nested Class Summary
Nested Classes

static interface

Preview.

A value layout whose carrier is boolean.class.

static interface

Preview.

A value layout whose carrier is byte.class.

static interface

Preview.

A value layout whose carrier is char.class.

static interface

Preview.

A value layout whose carrier is double.class.

static interface

Preview.

A value layout whose carrier is float.class.

static interface

Preview.

A value layout whose carrier is int.class.

static interface

Preview.

A value layout whose carrier is long.class.

static interface

Preview.

A value layout whose carrier is short.class.
Field Summary
Fields

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()
.

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()
.

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()
.

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()
.

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()
.

An unaligned value layout constant whose size is the same as that of a Java
char
and byte order set to
ByteOrder.nativeOrder()
.

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()
.

An unaligned value layout constant whose size is the same as that of a Java
double
and byte order set to
ByteOrder.nativeOrder()
.

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()
.

An unaligned value layout constant whose size is the same as that of a Java
float
and byte order set to
ByteOrder.nativeOrder()
.

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()
.

An unaligned value layout constant whose size is the same as that of a Java
int
and byte order set to
ByteOrder.nativeOrder()
.

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()
.

An unaligned value layout constant whose size is the same as that of a Java
long
and byte order set to
ByteOrder.nativeOrder()
.

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()
.

An unaligned value layout constant whose size is the same as that of a Java
short
and byte order set to
ByteOrder.nativeOrder()
.
Method Summary
Creates a strided var handle that can be used to access a memory segment as multi-dimensional array.

Returns the carrier associated with this value layout.

Returns the value's byte order.

Returns a memory layout with the same characteristics as this layout, but with the given alignment constraint (in bytes).

Returns a memory layout with the same characteristics as this layout, but with the given name.

Returns a value layout with the same characteristics as this layout, but with the given byte order.

Returns a memory layout with the same characteristics as this layout, but with no name.
Methods declared in interface java.lang.foreign.MemoryLayout^PREVIEWbyteAlignment, byteOffset, byteOffsetHandle, byteSize, equals, hashCode, name, select, sliceHandle, toString, varHandle

Field Details
- 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
  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
  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
  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
  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
  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
  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
  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
  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
  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
  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
  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
  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
  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
  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
  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
  Returns the value's byte order.
  
  Returns:
  
  the value's byte order
- withOrder
  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
  Returns a memory layout with the same characteristics as this layout, but with no name.
  Specified by:
  
  withoutName in interface MemoryLayout^PREVIEW
  
  Returns:
  
  a memory layout with the same characteristics as this layout, but with no name
  
  See Also:
  - MemoryLayout.name()^PREVIEW
- arrayElementVarHandle VarHandle arrayElementVarHandle(int... shape)
  Creates a
  strided
  var handle that can be used to access a memory segment as multi-dimensional array. This array has a notional sequence layout featuring
  shape.length
  nested sequence layouts. The element layout of the innermost sequence layout in the notional sequence layout is this value layout. The resulting var handle is obtained as if calling the
  MemoryLayout.varHandle(PathElement...)^PREVIEW
  method on the notional layout, with a layout path containing exactly
  shape.length + 1 open sequence layout path elements^PREVIEW
  .
  
  For instance, the following method call:
```
VarHandle arrayHandle = ValueLayout.JAVA_INT.arrayElementVarHandle(10, 20);
```
  Is equivalent to the following code:
```
 SequenceLayout notionalLayout = MemoryLayout.sequenceLayout(
                                         MemoryLayout.sequenceLayout(10, MemoryLayout.sequenceLayout(20, ValueLayout.JAVA_INT)));
 VarHandle arrayHandle = notionalLayout.varHandle(PathElement.sequenceElement(),
                                                  PathElement.sequenceElement(),
                                                  PathElement.sequenceElement());
```
  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 < notionalLayout.elementCount()
  - 0 <= y < 10
  - 0 <= z < 20
  Consider the following access expressions:
```
int value1 = (int) arrayHandle.get(10, 2, 4); // ok, accessed offset = 8176
int value2 = (int) 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 byteAlignment() > byteSize().
  
  See Also:
- carrier
  Returns the carrier associated with this value layout.
  
  Returns:
  
  the carrier associated with this value layout
- withName
  Returns a memory layout with the same characteristics as this layout, but with the given name.
  Specified by:
  
  withName in interface MemoryLayout^PREVIEW
  
  Parameters:
  
  name - the layout name.
  
  Returns:
  
  a memory layout with the same characteristics as this layout, but with the given name
  
  See Also:
  - MemoryLayout.name()^PREVIEW
- withByteAlignment
  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^PREVIEW
  
  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.

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