public static void checkState(boolean expression,Object errorMessage){
  if (ExoPlayerLibraryInfo.ASSERTIONS_ENABLED && !expression) {
    throw new IllegalStateException(String.valueOf(errorMessage));
  }
}

public static void checkState ( boolean expression , Object errorMessage ) { if ( ExoPlayerLibraryInfo . ASSERTIONS_ENABLED && ! expression ) { throw new IllegalStateException ( String . valueOf ( errorMessage ) ) ; } }
ensures the truth of an expression involving the state of the calling instance .
