How to use

checkFieldDescriptor

method

in

com.google.protobuf.MapEntry$Builder

@Override
public Message.Builder newBuilderForField(FieldDescriptor field) {
 checkFieldDescriptor(field);;
 // This method should be called for message fields and in a MapEntry
 // message only the value field can possibly be a message field.
 if (field.getNumber() != 2
   || field.getJavaType() != FieldDescriptor.JavaType.MESSAGE) {
  throw new RuntimeException(
    "\"" + field.getFullName() + "\" is not a message value field.");
 }
 return ((Message) value).newBuilderForType();
}

@SuppressWarnings("unchecked")
@Override
public Builder<K, V> setField(FieldDescriptor field, Object value) {
 checkFieldDescriptor(field);
 if (field.getNumber() == 1) {
  setKey((K) value);
 } else {
  if (field.getType() == FieldDescriptor.Type.ENUM) {
   value = ((EnumValueDescriptor) value).getNumber();
  } else if (field.getType() == FieldDescriptor.Type.MESSAGE) {
   if (value != null && !metadata.defaultValue.getClass().isInstance(value)) {
    // The value is not the exact right message type.  However, if it
    // is an alternative implementation of the same type -- e.g. a
    // DynamicMessage -- we should accept it.  In this case we can make
    // a copy of the message.
    value =
      ((Message) metadata.defaultValue).toBuilder().mergeFrom((Message) value).build();
   }
  }
  setValue((V) value);
 }
 return this;
}

@Override
public Message.Builder newBuilderForField(FieldDescriptor field) {
 checkFieldDescriptor(field);;
 // This method should be called for message fields and in a MapEntry
 // message only the value field can possibly be a message field.
 if (field.getNumber() != 2
   || field.getJavaType() != FieldDescriptor.JavaType.MESSAGE) {
  throw new RuntimeException(
    "\"" + field.getFullName() + "\" is not a message value field.");
 }
 return ((Message) value).newBuilderForType();
}

@Override
public Builder<K, V> clearField(FieldDescriptor field) {
 checkFieldDescriptor(field);
 if (field.getNumber() == 1) {
  clearKey();
 } else {
  clearValue();
 }
 return this;
}

@SuppressWarnings("unchecked")
@Override
public Builder<K, V> setField(FieldDescriptor field, Object value) {
 checkFieldDescriptor(field);
 if (field.getNumber() == 1) {
  setKey((K) value);
 } else {
  if (field.getType() == FieldDescriptor.Type.ENUM) {
   value = ((EnumValueDescriptor) value).getNumber();
  }
  setValue((V) value);
 }
 return this;
}

@Override
public Object getField(FieldDescriptor field) {
 checkFieldDescriptor(field);
 Object result = field.getNumber() == 1 ? getKey() : getValue();
 // Convert enums to EnumValueDescriptor.
 if (field.getType() == FieldDescriptor.Type.ENUM) {
  result = field.getEnumType().findValueByNumberCreatingIfUnknown((Integer) result);
 }
 return result;
}

@Override
public boolean hasField(FieldDescriptor field) {
 checkFieldDescriptor(field);
 return true;
}

@Override
public Object getField(FieldDescriptor field) {
 checkFieldDescriptor(field);
 Object result = field.getNumber() == 1 ? getKey() : getValue();
 // Convert enums to EnumValueDescriptor.
 if (field.getType() == FieldDescriptor.Type.ENUM) {
  result = field.getEnumType().findValueByNumberCreatingIfUnknown((Integer) result);
 }
 return result;
}

@Override
public boolean hasField(FieldDescriptor field) {
 checkFieldDescriptor(field);
 return field.getNumber() == 1 ? hasKey : hasValue;
}

@Override
public Builder<K, V> clearField(FieldDescriptor field) {
 checkFieldDescriptor(field);
 if (field.getNumber() == 1) {
  clearKey();
 } else {
  clearValue();
 }
 return this;
}