com.sun.jna
Class Structure

java.lang.Object
  com.sun.jna.Structure

Direct Known Subclasses:

Structure, Union

public abstract class Structure
extends Object

Represents a native structure with a Java peer class. When used as a function parameter or return value, this class corresponds to struct*. When used as a field within another Structure, it corresponds to struct. The tagging interfaces Structure.ByReference and Structure.ByValue may be used to alter the default behavior.

See the overview for supported type mappings.

Structure alignment and type mappings are derived by default from the enclosing interface definition (if any) by using Native.getStructureAlignment(java.lang.Class) and Native.getTypeMapper(java.lang.Class).

Structure fields corresponding to native fields must be public. The may additionally have the following modifiers:

• volatile JNA will not write the field unless specifically instructed to do so via writeField(String).
• final JNA will overwrite the field via read(), but otherwise the field is not modifiable from Java. Take care when using this option, since the compiler will usually assume all accesses to the field (for a given Structure instance) have the same value.

NOTE: Strings are used to represent native C strings because usage of char * is generally more common than wchar_t *.

NOTE: This class assumes that fields are returned in Class.getFields() in the same or reverse order as declared. If your VM returns them in no particular order, you're out of luck.

Author:

Todd Fast, todd.fast@sun.com, twall@users.sf.net

Nested Class Summary

static interface	Structure.ByReference Tagging interface to indicate the address of an instance of the Structure type is to be used within a Structure definition rather than nesting the full Structure contents.
static interface	Structure.ByValue Tagging interface to indicate the value of an instance of the Structure type is to be used in function invocations rather than its address.

Field Summary

static int	ALIGN_DEFAULT Use the platform default alignment.
static int	ALIGN_GNUC validated for 32-bit x86 linux/gcc; align field size, max 4 bytes
static int	ALIGN_MSVC validated for w32/msvc; align on field size
static int	ALIGN_NONE No alignment, place all fields on nearest 1-byte boundary
protected static int	CALCULATE_SIZE

Constructor Summary

protected	Structure()
protected	Structure(Pointer p) Create a structure cast onto pre-allocated memory.
protected	Structure(Pointer p, int alignment)
protected	Structure(Pointer p, int alignment, TypeMapper mapper)
protected	Structure(TypeMapper mapper)

Method Summary

protected void	allocateMemory() Attempt to allocate memory if sufficient information is available.
protected void	allocateMemory(int size) Provided for derived classes to indicate a different size than the default.
void	autoRead()
static void	autoRead(Structure[] ss)
void	autoWrite()
static void	autoWrite(Structure[] ss)
protected void	cacheTypeInfo(Pointer p)
void	clear()
protected void	ensureAllocated()
boolean	equals(Object o) This structure is equal to another based on the same data type and visible data fields.
boolean	getAutoRead() Returns whether the struture is written to native memory prior to a native function call.
boolean	getAutoWrite() Returns whether the structure is read from native memory after a native function call.
protected Integer	getBitsAnnotation(Field field) Override this in a subclass to support bit fields (@link http://en.wikipedia.org/wiki/C_syntax#Bit_fields) : package com.sun.jna; import java.lang.annotation
protected List	getFieldOrder()
protected int	getNativeAlignment(Class type, Object value, boolean isFirstElement) Overridable in subclasses.
Pointer	getPointer() Return a Pointer object to this structure.
protected int	getStructAlignment()
int	hashCode() Since equals(java.lang.Object) depends on the native address, use that as the hash code.
static Structure	newInstance(Class type) Create a new Structure instance of the given type
void	read() Reads the fields of the struct from native memory
Object	readField(String name) Force a read of the given field from native memory.
protected void	setAlignType(int alignType) Change the alignment of this structure.
void	setAutoRead(boolean auto) Set whether the struture is written to native memory prior to a native function call.
void	setAutoSynch(boolean auto) Set whether the structure is automatically synched to native memory before and after a native function call.
void	setAutoWrite(boolean auto) Set whether the structure is read from native memory after a native function call.
protected void	setFieldOrder(String[] fields) Provided for VMs where the field order as returned by Class.getFields() is not predictable.
protected void	setTypeMapper(TypeMapper mapper) Change the type mapping for this structure.
int	size()
protected void	sortFields(Field[] fields, String[] names) Sort the structure fields according to the given array of names.
Structure[]	toArray(int size) Returns a view of this structure's memory as an array of structures.
Structure[]	toArray(Structure[] array) Returns a view of this structure's memory as an array of structures.
String	toString()
protected void	useMemory(Pointer m) Set the memory used by this structure.
protected void	useMemory(Pointer m, int offset) Set the memory used by this structure.
void	write() Writes the fields of the struct to native memory
void	writeField(String name) Write the given field to native memory.
void	writeField(String name, Object value) Write the given field value to the field and native memory.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

ALIGN_DEFAULT

public static final int ALIGN_DEFAULT

Use the platform default alignment.

See Also:

Constant Field Values

ALIGN_NONE

public static final int ALIGN_NONE

No alignment, place all fields on nearest 1-byte boundary

See Also:

Constant Field Values

ALIGN_GNUC

public static final int ALIGN_GNUC

validated for 32-bit x86 linux/gcc; align field size, max 4 bytes

See Also:

Constant Field Values

ALIGN_MSVC

public static final int ALIGN_MSVC

validated for w32/msvc; align on field size

See Also:

Constant Field Values

CALCULATE_SIZE

protected static final int CALCULATE_SIZE

See Also:

Constant Field Values

Constructor Detail

Structure

protected Structure()

Structure

protected Structure(TypeMapper mapper)

Structure

protected Structure(Pointer p)

Create a structure cast onto pre-allocated memory.

Structure

protected Structure(Pointer p,
                    int alignment)

Structure

protected Structure(Pointer p,
                    int alignment,
                    TypeMapper mapper)

Method Detail

setTypeMapper

protected void setTypeMapper(TypeMapper mapper)

Change the type mapping for this structure. May cause the structure to be resized and any existing memory to be reallocated. If null, the default mapper for the defining class will be used.

setAlignType

protected void setAlignType(int alignType)

Change the alignment of this structure. Re-allocates memory if necessary. If alignment is ALIGN_DEFAULT, the default alignment for the defining class will be used.

useMemory

protected void useMemory(Pointer m)

Set the memory used by this structure. This method is used to indicate the given structure is nested within another or otherwise overlaid on some other memory block and thus does not own its own memory.

useMemory

protected void useMemory(Pointer m,
                         int offset)

Set the memory used by this structure. This method is used to indicate the given structure is nested within another or otherwise overlaid on some other memory block and thus does not own its own memory.

ensureAllocated

protected void ensureAllocated()

allocateMemory

protected void allocateMemory()

Attempt to allocate memory if sufficient information is available. Returns whether the operation was successful.

allocateMemory

protected void allocateMemory(int size)

Provided for derived classes to indicate a different size than the default. Returns whether the operation was successful. Will leave memory untouched if it is non-null and not allocated by this class.

size

public int size()

clear

public void clear()

getPointer

public Pointer getPointer()

Return a Pointer object to this structure. Note that if you use the structure's pointer as a function argument, you are responsible for calling write() prior to the call and read() after the call. These calls are normally handled automatically by the Function object when it encounters a Structure argument or return value.

read

public void read()

Reads the fields of the struct from native memory

readField

public Object readField(String name)

Force a read of the given field from native memory. The Java field will be updated from the current contents of native memory.

Returns:

the new field value, after updating

Throws:

IllegalArgumentException - if no field exists with the given name

write

public void write()

Writes the fields of the struct to native memory

writeField

public void writeField(String name)

Write the given field to native memory. The current value in the Java field will be translated into native memory.

Throws:

IllegalArgumentException - if no field exists with the given name

writeField

public void writeField(String name,
                       Object value)

Write the given field value to the field and native memory. The given value will be written both to the Java field and the corresponding native memory.

Throws:

IllegalArgumentException - if no field exists with the given name

getFieldOrder

protected List getFieldOrder()

setFieldOrder

protected void setFieldOrder(String[] fields)

Provided for VMs where the field order as returned by Class.getFields() is not predictable.

sortFields

protected void sortFields(Field[] fields,
                          String[] names)

Sort the structure fields according to the given array of names.

getBitsAnnotation

protected Integer getBitsAnnotation(Field field)

Override this in a subclass to support bit fields (@link http://en.wikipedia.org/wiki/C_syntax#Bit_fields) : package com.sun.jna; import java.lang.annotation.*;

getStructAlignment

protected int getStructAlignment()

getNativeAlignment

protected int getNativeAlignment(Class type,
                                 Object value,
                                 boolean isFirstElement)

Overridable in subclasses.

toString

public String toString()

Overrides:

toString in class Object

toArray

public Structure[] toArray(Structure[] array)

Returns a view of this structure's memory as an array of structures. Note that this Structure must have a public, no-arg constructor. If the structure is currently using auto-allocated Memory backing, the memory will be resized to fit the entire array.

toArray

public Structure[] toArray(int size)

Returns a view of this structure's memory as an array of structures. Note that this Structure must have a public, no-arg constructor. If the structure is currently using auto-allocated Memory backing, the memory will be resized to fit the entire array.

equals

public boolean equals(Object o)

This structure is equal to another based on the same data type and visible data fields.

Overrides:

equals in class Object

hashCode

public int hashCode()

Since equals(java.lang.Object) depends on the native address, use that as the hash code.

Overrides:

hashCode in class Object

cacheTypeInfo

protected void cacheTypeInfo(Pointer p)

setAutoSynch

public void setAutoSynch(boolean auto)

Set whether the structure is automatically synched to native memory before and after a native function call. Convenience method for

        boolean auto = ...;
        setAutoRead(auto);
        setAutoWrite(auto);
        

setAutoRead

public void setAutoRead(boolean auto)

Set whether the struture is written to native memory prior to a native function call.

getAutoRead

public boolean getAutoRead()

Returns whether the struture is written to native memory prior to a native function call.

setAutoWrite

public void setAutoWrite(boolean auto)

Set whether the structure is read from native memory after a native function call.

getAutoWrite

public boolean getAutoWrite()

Returns whether the structure is read from native memory after a native function call.

newInstance

public static Structure newInstance(Class type)
                             throws IllegalArgumentException

Create a new Structure instance of the given type

Parameters:

type -

Returns:

the new instance

Throws:

IllegalArgumentException - if the instantiation fails

autoRead

public static void autoRead(Structure[] ss)

autoRead

public void autoRead()

autoWrite

public static void autoWrite(Structure[] ss)

autoWrite

public void autoWrite()