third_party/protobuf/3.6.1/java/core/src/main/java/com/google/protobuf/LazyField.java

// Protocol Buffers - Google's data interchange format
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// https://developers.google.com/protocol-buffers/
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package com.google.protobuf;

import java.util.Iterator;
import java.util.Map.Entry;

/**
 * LazyField encapsulates the logic of lazily parsing message fields. It stores
 * the message in a ByteString initially and then parse it on-demand.
 *
 * Most of key methods are implemented in {@link LazyFieldLite} but this class
 * can contain default instance of the message to provide {@code hashCode()},
 * {@code euqals()} and {@code toString()}.
 *
 * @author xiangl@google.com (Xiang Li)
 */
public class LazyField extends LazyFieldLite {

  /**
   * Carry a message's default instance which is used by {@code hashCode()}, {@code euqals()} and
   * {@code toString()}.
   */
  private final MessageLite defaultInstance;

  public LazyField(MessageLite defaultInstance,
      ExtensionRegistryLite extensionRegistry, ByteString bytes) {
    super(extensionRegistry, bytes);

    this.defaultInstance = defaultInstance;
  }

  @Override
  public boolean containsDefaultInstance() {
    return super.containsDefaultInstance() || value == defaultInstance;
  }

  public MessageLite getValue() {
    return getValue(defaultInstance);
  }

  @Override
  public int hashCode() {
    return getValue().hashCode();
  }

  @Override
  public boolean equals(Object obj) {
    return getValue().equals(obj);
  }

  @Override
  public String toString() {
    return getValue().toString();
  }

  // ====================================================

  /**
   * LazyEntry and LazyIterator are used to encapsulate the LazyField, when
   * users iterate all fields from FieldSet.
   */
  static class LazyEntry<K> implements Entry<K, Object> {
    private Entry<K, LazyField> entry;

    private LazyEntry(Entry<K, LazyField> entry) {
      this.entry = entry;
    }

    @Override
    public K getKey() {
      return entry.getKey();
    }

    @Override
    public Object getValue() {
      LazyField field = entry.getValue();
      if (field == null) {
        return null;
      }
      return field.getValue();
    }

    public LazyField getField() {
      return entry.getValue();
    }

    @Override
    public Object setValue(Object value) {
      if (!(value instanceof MessageLite)) {
        throw new IllegalArgumentException(
            "LazyField now only used for MessageSet, "
            + "and the value of MessageSet must be an instance of MessageLite");
      }
      return entry.getValue().setValue((MessageLite) value);
    }
  }

  static class LazyIterator<K> implements Iterator<Entry<K, Object>> {
    private Iterator<Entry<K, Object>> iterator;

    public LazyIterator(Iterator<Entry<K, Object>> iterator) {
      this.iterator = iterator;
    }

    @Override
    public boolean hasNext() {
      return iterator.hasNext();
    }

    @Override
    @SuppressWarnings("unchecked")
    public Entry<K, Object> next() {
      Entry<K, ?> entry = iterator.next();
      if (entry.getValue() instanceof LazyField) {
        return new LazyEntry<K>((Entry<K, LazyField>) entry);
      }
      return (Entry<K, Object>) entry;
    }

    @Override
    public void remove() {
      iterator.remove();
    }
  }
}