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/* Copyright (c) 2007-2012 Timothy Wall, All Rights Reserved
*
* The contents of this file is dual-licensed under 2
* alternative Open Source/Free licenses: LGPL 2.1 or later and
* Apache License 2.0. (starting with JNA version 4.0.0).
*
* You can freely decide which license you want to apply to
* the project.
*
* You may obtain a copy of the LGPL License at:
*
* http://www.gnu.org/licenses/licenses.html
*
* A copy is also included in the downloadable source code package
* containing JNA, in file "LGPL2.1".
*
* You may obtain a copy of the Apache License at:
*
* http://www.apache.org/licenses/
*
* A copy is also included in the downloadable source code package
* containing JNA, in file "AL2.0".
*/
package com.sun.jna;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
/** Represents a native union. When writing to native memory, the field
* corresponding to the type passed to {@link #setType} 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 {@link #setType}. 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.
*/
public abstract class Union extends Structure {
private StructField activeField;
/** Create a Union whose size and alignment will be calculated
* automatically.
*/
protected Union() { }
/** Create a Union of the given size, using default alignment. */
protected Union(Pointer p) {
super(p);
}
/** Create a Union of the given size and alignment type. */
protected Union(Pointer p, int alignType) {
super(p, alignType);
}
/** Create a Union of the given size and alignment type. */
protected Union(TypeMapper mapper) {
super(mapper);
}
/** Create a Union of the given size and alignment type. */
protected Union(Pointer p, int alignType, TypeMapper mapper) {
super(p, alignType, mapper);
}
/** Unions do not need a field order, so automatically provide a value to
* satisfy checking in the Structure superclass.
*/
@Override
protected List getFieldOrder() {
List flist = getFieldList();
List list = new ArrayList(flist.size());
for (Field f : flist) {
list.add(f.getName());
}
return list;
}
/** Indicates by type which field will be used to write to native memory.
* If there are multiple fields of the same type, use {@link
* #setType(String)} instead with the field name.
* @param type desired active type for the union
* @throws IllegalArgumentException if the type does not correspond to
* any declared union field.
*/
public void setType(Class type) {
ensureAllocated();
for (StructField f : fields().values()) {
if (f.type == type) {
activeField = f;
return;
}
}
throw new IllegalArgumentException("No field of type " + type + " in " + this);
}
/**
* Indicates which field will be used to write to native memory.
* @param fieldName desired field to use for the active union type
* @throws IllegalArgumentException if the name does not correspond to
* any declared union field.
*/
public void setType(String fieldName) {
ensureAllocated();
StructField f = fields().get(fieldName);
if (f != null) {
activeField = f;
}
else {
throw new IllegalArgumentException("No field named " + fieldName
+ " in " + this);
}
}
/** Force a read of the given field from native memory.
* @return the new field value, after updating
* @throws IllegalArgumentException if no field exists with the given name
*/
@Override
public Object readField(String fieldName) {
ensureAllocated();
setType(fieldName);
return super.readField(fieldName);
}
/** Write the given field value to native memory.
* The given field will become the active one.
* @throws IllegalArgumentException if no field exists with the given name
*/
@Override
public void writeField(String fieldName) {
ensureAllocated();
setType(fieldName);
super.writeField(fieldName);
}
/** Write the given field value to the field and native memory.
* The given field will become the active one.
* @throws IllegalArgumentException if no field exists with the given name
*/
@Override
public void writeField(String fieldName, Object value) {
ensureAllocated();
setType(fieldName);
super.writeField(fieldName, value);
}
/** 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;
*
* @param type class type of the Structure field to read
* @return the Structure field with the given type
*/
public Object getTypedValue(Class type) {
ensureAllocated();
for (StructField f : fields().values()) {
if (f.type == type) {
activeField = f;
read();
return getFieldValue(activeField.field);
}
}
throw new IllegalArgumentException("No field of type " + type + " in " + this);
}
/** Set the active type and its value. Convenience method for
*
* Union u;
* Class type;
* u.setType(type);
* u.field = value;
*
* @param object instance of a class which is part of the union
* @return this Union object
*/
public Object setTypedValue(Object object) {
StructField f = findField(object.getClass());
if (f != null) {
activeField = f;
setFieldValue(f.field, object);
return this;
}
throw new IllegalArgumentException("No field of type " + object.getClass() + " in " + this);
}
/** Returns the field in this union with the same type as type,
* if any, null otherwise.
* @param type type to search for
* @return StructField of matching type
*/
private StructField findField(Class type) {
ensureAllocated();
for (StructField f : fields().values()) {
if (f.type.isAssignableFrom(type)) {
return f;
}
}
return null;
}
/** Only the currently selected field will be written. */
@Override
protected void writeField(StructField field) {
if (field == activeField) {
super.writeField(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.
*/
@Override
protected Object readField(StructField field) {
if (field == activeField
|| (!Structure.class.isAssignableFrom(field.type)
&& !String.class.isAssignableFrom(field.type)
&& !WString.class.isAssignableFrom(field.type))) {
return super.readField(field);
}
// Field not accessible
// TODO: read by-value structures, to the extent possible; need a
// "read cautiously" method to "read" to indicate we want to avoid
// pointer-based fields
return null;
}
/** All fields are considered the "first" element. */
@Override
protected int getNativeAlignment(Class type, Object value, boolean isFirstElement) {
return super.getNativeAlignment(type, value, true);
}
}
