@Override
  public String toString() {
    if (dex == null) {
      return methodHandleType + " " + fieldOrMethodId;
    }
    return methodHandleType
        + " "
        + (methodHandleType.isField()
            ? dex.fieldIds().get(fieldOrMethodId)
            : dex.methodIds().get(fieldOrMethodId));
  }
A method_handle_item:
https://source.android.com/devices/tech/dalvik/dex-format#method-handle-item
android/android_framework/dex-maker/src/main/java/com/android/dex/MethodHandle.java