com.sun.jna
Class Union

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

public abstract class Union
extends Structure

Represents a native union. When writing to native memory, the field corresponding to the type passed to setType(java.lang.Class) will be written to native memory. Upon reading from native memory, Structure, String, or WString fields will not be initialized unless they are the current field as identified by a call to setType(java.lang.Class). The current field is always unset by default to avoid accidentally attempting to read a field that is not valid. In the case of a String, for instance, an invalid pointer may result in a memory fault when attempting to initialize the String.

Nested Class Summary

Nested classes/interfaces inherited from class com.sun.jna.Structure

Structure.ByReference, Structure.ByValue, Structure.FFIType, Structure.StructField

Field Summary

(package private) Structure.StructField

biggestField

Fields inherited from class com.sun.jna.Structure

ALIGN_DEFAULT, ALIGN_GNUC, ALIGN_MSVC, ALIGN_NONE, CALCULATE_SIZE, isPPC, isSPARC

Constructor Summary

protected	Union() Create a Union whose size and alignment will be calculated automatically.
protected	Union(Pointer p) Create a Union of the given size, using default alignment.
protected	Union(Pointer p, int alignType) Create a Union of the given size and alignment type.
protected	Union(Pointer p, int alignType, TypeMapper mapper) Create a Union of the given size and alignment type.
protected	Union(TypeMapper mapper) Create a Union of the given size and alignment type.

Method Summary

(package private) int	calculateSize(boolean force) Adjust the size to be the size of the largest element, and ensure all fields begin at offset zero.
protected int	getNativeAlignment(java.lang.Class type, java.lang.Object value, boolean isFirstElement) All fields are considered the "first" element.
java.lang.Object	getTypedValue(java.lang.Class type) Reads the Structure field of the given type from memory, sets it as the active type and returns it.
(package private) Pointer	getTypeInfo() Avoid calculating type information until we know our biggest field.
java.lang.Object	readField(java.lang.String name) Force a read of the given field from native memory.
(package private) java.lang.Object	readField(Structure.StructField field) Avoid reading pointer-based fields and structures unless explicitly selected.
void	setType(java.lang.Class type) Indicates which field will be used to write to native memory.
java.lang.Object	setTypedValue(java.lang.Object object) Set the active type and its value.
void	writeField(java.lang.String name) Write the given field value to native memory.
void	writeField(java.lang.String name, java.lang.Object value) Write the given field value to the field and native memory.
(package private) void	writeField(Structure.StructField field) Only the currently selected field will be written.

Methods inherited from class com.sun.jna.Structure

allocateMemory, allocateMemory, autoAllocate, autoRead, autoRead, autoWrite, autoWrite, busy, cacheTypeInfo, calculateAlignedSize, clear, ensureAllocated, equals, fields, getAutoRead, getAutoWrite, getField, getFieldOrder, getFields, getPointer, getStructAlignment, getTypeInfo, hashCode, newInstance, read, reading, setAlignType, setAutoRead, setAutoSynch, setAutoWrite, setField, setFieldOrder, setTypeMapper, size, sortFields, toArray, toArray, toString, updateStructureByReference, useMemory, useMemory, write

Methods inherited from class java.lang.Object

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

Field Detail

biggestField

Structure.StructField biggestField

Constructor Detail

Union

protected Union()

Create a Union whose size and alignment will be calculated automatically.

Union

protected Union(Pointer p)

Create a Union of the given size, using default alignment.

Union

protected Union(Pointer p,
                int alignType)

Create a Union of the given size and alignment type.

Union

protected Union(TypeMapper mapper)

Create a Union of the given size and alignment type.

Union

protected Union(Pointer p,
                int alignType,
                TypeMapper mapper)

Create a Union of the given size and alignment type.

Method Detail

setType

public void setType(java.lang.Class type)

Indicates which field will be used to write to native memory.

Throws:

java.lang.IllegalArgumentException - if the type does not correspond to any declared union field.

readField

public java.lang.Object readField(java.lang.String name)

Force a read of the given field from native memory.

Overrides:

readField in class Structure

Returns:

the new field value, after updating

Throws:

java.lang.IllegalArgumentException - if no field exists with the given name

writeField

public void writeField(java.lang.String name)

Write the given field value to native memory. The given field will become the active one.

Overrides:

writeField in class Structure

Throws:

java.lang.IllegalArgumentException - if no field exists with the given name

writeField

public void writeField(java.lang.String name,
                       java.lang.Object value)

Write the given field value to the field and native memory. The given field will become the active one.

Overrides:

writeField in class Structure

Throws:

java.lang.IllegalArgumentException - if no field exists with the given name

getTypedValue

public java.lang.Object getTypedValue(java.lang.Class type)

Reads the Structure field of the given type from memory, sets it as the active type and returns it. Convenience method for

 Union u;
 Class type;
 u.setType(type);
 u.read();
 value = u.field;
 

Parameters:

type - class type of the Structure field to read

Returns:

the Structure field with the given type

setTypedValue

public java.lang.Object setTypedValue(java.lang.Object object)

Set the active type and its value. Convenience method for

 Union u;
 Class type;
 u.setType(type);
 u.field = value;
 

Parameters:

object - instance of a class which is part of the union

Returns:

this Union object

writeField

void writeField(Structure.StructField field)

Only the currently selected field will be written.

Overrides:

writeField in class Structure

readField

java.lang.Object readField(Structure.StructField field)

Avoid reading pointer-based fields and structures unless explicitly selected. Structures may contain pointer-based fields which can crash the VM if not properly initialized.

Overrides:

readField in class Structure

calculateSize

int calculateSize(boolean force)

Adjust the size to be the size of the largest element, and ensure all fields begin at offset zero.

Overrides:

calculateSize in class Structure

getNativeAlignment

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

All fields are considered the "first" element.

Overrides:

getNativeAlignment in class Structure

getTypeInfo

Pointer getTypeInfo()

Avoid calculating type information until we know our biggest field. Return type information for the largest field to ensure all available bits are used.

Overrides:

getTypeInfo in class Structure