public Builder setLinearVelocity(
          org.box2d.proto.Box2D.PbVec2.Builder builderForValue) {
        if (linearVelocityBuilder_ == null) {
          linearVelocity_ = builderForValue.build();
          onChanged();
        } else {
          linearVelocityBuilder_.setMessage(builderForValue.build());
        }
        bitField0_ |= 0x00000010;
        return this;
      }