Package com.sun.jna

# Class Union

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

Direct Known Subclasses:
  `Kstat2.Kstat2NV.UNION`, `LibKstat.KstatNamed.UNION`, `Ntifs.REPARSE_DATA_BUFFER.REPARSE_UNION`, `NTSecApi.LSA_FOREST_TRUST_RECORD.UNION`, `OaIdl.BINDPTR`, `OaIdl.CURRENCY`, `OaIdl.DECIMAL._DECIMAL1`, `OaIdl.DECIMAL._DECIMAL2`, `OaIdl.ELEMDESC._ELEMDESC`, `OaIdl.TYPEDESC._TYPEDESC`, `OaIdl.VARDESC._VARDESC`, `Perfstat.perfstat_protocol_t.AnonymousUnionPayload`, `ShTypes.STRRET.UNION`, `Variant.VARIANT`, `Variant.VARIANT._VARIANT.__VARIANT`, `WinBase.SYSTEM_INFO.UNION`, `Wincon.INPUT_RECORD.Event`, `WinCrypt.CERT_STRONG_SIGN_PARA.DUMMYUNION`, `Winevt.EVT_VARIANT.field1_union`, `Wininet.INTERNET_CACHE_ENTRY_INFO.UNION`, `WinNT.LARGE_INTEGER.UNION`, `WinNT.SYSTEM_LOGICAL_PROCESSOR_INFORMATION.AnonymousUnionPayload`, `WinRas.RASTUNNELENDPOINT.UNION`, `Winspool.NOTIFY_DATA`, `WinUser.INPUT.INPUT_UNION`, `X11.XClientMessageEvent.Data`, `X11.XEvent`

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.FieldOrder, Structure.StructField, Structure.StructureSet`

## Field Summary

### Fields inherited from class com.sun.jna.Structure

`ALIGN_DEFAULT, ALIGN_GNUC, ALIGN_MSVC, ALIGN_NONE, CALCULATE_SIZE, fieldOrder, layoutInfo`

## Constructor Summary

Constructors
Modifier
Constructor
Description
`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

Modifier and Type
Method
Description
`protected List<String>`
`getFieldOrder()`
Unions do not need a field order, so automatically provide a value to satisfy checking in the Structure superclass.
`protected int`
`getNativeAlignment(Class<?> type, Object value, boolean isFirstElement)`
All fields are considered the "first" element.
`Object`
`getTypedValue(Class<?> type)`
Reads the Structure field of the given type from memory, sets it as the active type and returns it.
`protected Object`
`readField(Structure.StructField field)`
Avoid reading pointer-based fields and structures unless explicitly selected.
`Object`
`readField(String fieldName)`
Force a read of the given field from native memory.
`void`
`setType(Class<?> type)`
Indicates by type which field will be used to write to native memory.
`void`
`setType(String fieldName)`
Indicates which field will be used to write to native memory.
`Object`
`setTypedValue(Object object)`
Set the active type and its value.
`protected void`
`writeField(Structure.StructField field)`
Only the currently selected field will be written.
`void`
`writeField(String fieldName)`
Write the given field value to native memory.
`void`
`writeField(String fieldName, Object value)`
Write the given field value to the field and native memory.

### Methods inherited from class com.sun.jna.Structure

`allocateMemory, allocateMemory, autoAllocate, autoRead, autoRead, autoWrite, autoWrite, busy, cacheTypeInfo, calculateSize, calculateSize, clear, conditionalAutoRead, createFieldsOrder, createFieldsOrder, createFieldsOrder, createFieldsOrder, dataEquals, dataEquals, ensureAllocated, equals, fieldOffset, fields, getAutoRead, getAutoWrite, getFieldList, getFields, getFieldTypeInfo, getFieldValue, getNativeSize, getNativeSize, getPointer, getStringEncoding, getStructAlignment, getTypeInfo, getTypeInfo, getTypeMapper, hashCode, newInstance, newInstance, read, reading, setAlignType, setAutoRead, setAutoSynch, setAutoWrite, setFieldValue, setStringEncoding, size, size, size, sortFields, toArray, toArray, toString, toString, updateStructureByReference, useMemory, useMemory, useMemory, validate, write`

### Methods inherited from class java.lang.Object

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

## Constructor Details

### 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 Details

### getFieldOrder

protected List<String> getFieldOrder()
Unions do not need a field order, so automatically provide a value to satisfy checking in the Structure superclass.

Overrides:
  `getFieldOrder` in class `Structure`
Returns:
  ordered list of field names

### setType

public void setType(Class<?> type)
Indicates by type which field will be used to write to native memory. If there are multiple fields of the same type, use `setType(String)` instead with the field name.

Parameters:
  `type` - desired active type for the union
Throws:
  `IllegalArgumentException` - if the type does not correspond to any declared union field.

### setType

public void setType(String fieldName)
Indicates which field will be used to write to native memory.

Parameters:
  `fieldName` - desired field to use for the active union type
Throws:
  `IllegalArgumentException` - if the name does not correspond to any declared union field.

### readField

public Object readField(String fieldName)
Force a read of the given field from native memory.

Overrides:
  `readField` in class `Structure`
Parameters:
  `fieldName` - field to be read
Returns:
  the new field value, after updating
Throws:
  `IllegalArgumentException` - if no field exists with the given name

### writeField

public void writeField(String fieldName)
Write the given field value to native memory. The given field will become the active one.

Overrides:
  `writeField` in class `Structure`
Parameters:
  `fieldName` - which field to synch
Throws:
  `IllegalArgumentException` - if no field exists with the given name

### writeField

public void writeField(String fieldName, 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`
Parameters:
  `fieldName` - field to write
  `value` - value to write
Throws:
  `IllegalArgumentException` - if no field exists with the given name

### getTypedValue

public Object getTypedValue(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 Object setTypedValue(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

protected void writeField(Structure.StructField field)
Only the currently selected field will be written.

Overrides:
  `writeField` in class `Structure`
Parameters:
  `field` - internal field representation to synch to native memory

### readField

protected 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`
Parameters:
  `field` - field to be read
Returns:
  value of the requested field

### getNativeAlignment

protected int getNativeAlignment(Class<?> type, Object value, boolean isFirstElement)
All fields are considered the "first" element.

Overrides:
  `getNativeAlignment` in class `Structure`
Parameters:
  `type` - field type
  `value` - field value, if available
  `isFirstElement` - is this field the first element in the struct?
Returns:
  the native byte alignment