public Builder clear() {
        super.clear();
        tag_ = 0L;
        bitField0_ = (bitField0_ & ~0x00000001);
        if (gravityBuilder_ == null) {
          gravity_ = org.box2d.proto.Box2D.PbVec2.getDefaultInstance();
        } else {
          gravityBuilder_.clear();
        }
        bitField0_ = (bitField0_ & ~0x00000002);
        allowSleep_ = false;
        bitField0_ = (bitField0_ & ~0x00000004);
        autoClearForces_ = false;
        bitField0_ = (bitField0_ & ~0x00000008);
        warmStarting_ = false;
        bitField0_ = (bitField0_ & ~0x00000010);
        continuousPhysics_ = false;
        bitField0_ = (bitField0_ & ~0x00000020);
        subStepping_ = false;
        bitField0_ = (bitField0_ & ~0x00000040);
        if (bodiesBuilder_ == null) {
          bodies_ = java.util.Collections.emptyList();
          bitField0_ = (bitField0_ & ~0x00000080);
        } else {
          bodiesBuilder_.clear();
        }
        if (jointsBuilder_ == null) {
          joints_ = java.util.Collections.emptyList();
          bitField0_ = (bitField0_ & ~0x00000100);
        } else {
          jointsBuilder_.clear();
        }
        return this;
      }