// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// http://code.google.com/p/protobuf/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
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//
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package com.google.protobuf;
/**
* {@code SingleFieldBuilder} implements a structure that a protocol
* message uses to hold a single field of another protocol message. It supports
* the classical use case of setting an immutable {@link Message} as the value
* of the field and is highly optimized around this.
* <br>
* It also supports the additional use case of setting a {@link Message.Builder}
* as the field and deferring conversion of that {@code Builder}
* to an immutable {@code Message}. In this way, it's possible to maintain
* a tree of {@code Builder}'s that acts as a fully read/write data
* structure.
* <br>
* Logically, one can think of a tree of builders as converting the entire tree
* to messages when build is called on the root or when any method is called
* that desires a Message instead of a Builder. In terms of the implementation,
* the {@code SingleFieldBuilder} and {@code RepeatedFieldBuilder}
* classes cache messages that were created so that messages only need to be
* created when some change occured in its builder or a builder for one of its
* descendants.
*
* @param <MType> the type of message for the field
* @param <BType> the type of builder for the field
* @param <IType> the common interface for the message and the builder
*
* @author jonp@google.com (Jon Perlow)
*/
public class SingleFieldBuilder
<MType extends GeneratedMessage,
BType extends GeneratedMessage.Builder,
IType extends MessageOrBuilder>
implements GeneratedMessage.BuilderParent {
// Parent to send changes to.
private GeneratedMessage.BuilderParent parent;
// Invariant: one of builder or message fields must be non-null.
// If set, this is the case where we are backed by a builder. In this case,
// message field represents a cached message for the builder (or null if
// there is no cached message).
private BType builder;
// If builder is non-null, this represents a cached message from the builder.
// If builder is null, this is the authoritative message for the field.
private MType message;
// Indicates that we've built a message and so we are now obligated
// to dispatch dirty invalidations. See GeneratedMessage.BuilderListener.
private boolean isClean;
public SingleFieldBuilder(
MType message,
GeneratedMessage.BuilderParent parent,
boolean isClean) {
if (message == null) {
throw new NullPointerException();
}
this.message = message;
this.parent = parent;
this.isClean = isClean;
}
public void dispose() {
// Null out parent so we stop sending it invalidations.
parent = null;
}
/**
* Get the message for the field. If the message is currently stored
* as a {@code Builder}, it is converted to a {@code Message} by
* calling {@link Message.Builder#buildPartial} on it. If no message has
* been set, returns the default instance of the message.
*
* @return the message for the field
*/
@SuppressWarnings("unchecked")
public MType getMessage() {
if (message == null) {
// If message is null, the invariant is that we must be have a builder.
message = (MType) builder.buildPartial();
}
return message;
}
/**
* Builds the message and returns it.
*
* @return the message
*/
public MType build() {
// Now that build has been called, we are required to dispatch
// invalidations.
isClean = true;
return getMessage();
}
/**
* Gets a builder for the field. If no builder has been created yet, a
* builder is created on demand by calling {@link Message#toBuilder}.
*
* @return The builder for the field
*/
@SuppressWarnings("unchecked")
public BType getBuilder() {
if (builder == null) {
// builder.mergeFrom() on a fresh builder
// does not create any sub-objects with independent clean/dirty states,
// therefore setting the builder itself to clean without actually calling
// build() cannot break any invariants.
builder = (BType) message.newBuilderForType(this);
builder.mergeFrom(message); // no-op if message is the default message
builder.markClean();
}
return builder;
}
/**
* Gets the base class interface for the field. This may either be a builder
* or a message. It will return whatever is more efficient.
*
* @return the message or builder for the field as the base class interface
*/
@SuppressWarnings("unchecked")
public IType getMessageOrBuilder() {
if (builder != null) {
return (IType) builder;
} else {
return (IType) message;
}
}
/**
* Sets a message for the field replacing any existing value.
*
* @param message the message to set
* @return the builder
*/
public SingleFieldBuilder<MType, BType, IType> setMessage(
MType message) {
if (message == null) {
throw new NullPointerException();
}
this.message = message;
if (builder != null) {
builder.dispose();
builder = null;
}
onChanged();
return this;
}
/**
* Merges the field from another field.
*
* @param value the value to merge from
* @return the builder
*/
public SingleFieldBuilder<MType, BType, IType> mergeFrom(
MType value) {
if (builder == null && message == message.getDefaultInstanceForType()) {
message = value;
} else {
getBuilder().mergeFrom(value);
}
onChanged();
return this;
}
/**
* Clears the value of the field.
*
* @return the builder
*/
@SuppressWarnings("unchecked")
public SingleFieldBuilder<MType, BType, IType> clear() {
message = (MType) (message != null ?
message.getDefaultInstanceForType() :
builder.getDefaultInstanceForType());
if (builder != null) {
builder.dispose();
builder = null;
}
onChanged();
return this;
}
/**
* Called when a the builder or one of its nested children has changed
* and any parent should be notified of its invalidation.
*/
private void onChanged() {
// If builder is null, this is the case where onChanged is being called
// from setMessage or clear.
if (builder != null) {
message = null;
}
if (isClean && parent != null) {
parent.markDirty();
// Don't keep dispatching invalidations until build is called again.
isClean = false;
}
}
//@Override (Java 1.6 override semantics, but we must support 1.5)
public void markDirty() {
onChanged();
}
}