SingleFieldBuilder.java

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// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// 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
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
package com.google.protobuf;
 
import static com.google.protobuf.Internal.checkNotNull;
 
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) {
    this.message = checkNotNull(message);
    this.parent = parent;
    this.isClean = isClean;
  }
 
  public void dispose() {
    // Null out parent so we stop sending it invalidations.
    parent = null;
  }
 
  @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;
  }
 
  public MType build() {
    // Now that build has been called, we are required to dispatch
    // invalidations.
    isClean = true;
    return getMessage();
  }
 
  @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;
  }
 
  @SuppressWarnings("unchecked")
  public IType getMessageOrBuilder() {
    if (builder != null) {
      return (IType) builder;
    } else {
      return (IType) message;
    }
  }
 
  public SingleFieldBuilder<MType, BType, IType> setMessage(MType message) {
    this.message = checkNotNull(message);
    if (builder != null) {
      builder.dispose();
      builder = null;
    }
    onChanged();
    return this;
  }
 
  public SingleFieldBuilder<MType, BType, IType> mergeFrom(MType value) {
    if (builder == null && message == message.getDefaultInstanceForType()) {
      message = value;
    } else {
      getBuilder().mergeFrom(value);
    }
    onChanged();
    return this;
  }
 
  @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;
  }
 
  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
  public void markDirty() {
    onChanged();
  }
}