1. public DataStreamSource<T> setParallelism(int parallelism) {
    2.     OperatorValidationUtils.validateParallelism(parallelism, this.isParallel);
    3.     super.setParallelism(parallelism);
    4.     return this;
    5. }
    6. public static void validateParallelism(int parallelism, boolean canBeParallel) {
    7.     Preconditions.checkArgument(canBeParallel || parallelism == 1, "The parallelism of non parallel operator must be 1.");
    8.     Preconditions.checkArgument(parallelism > 0 || parallelism == -1, "The parallelism of an operator must be at least 1, or ExecutionConfig.PARALLELISM_DEFAULT (use system default).");
    9. }