@PublicEvolving
	public SingleOutputStreamOperator<T> forceNonParallel() {
		transformation.setParallelism(1);
		transformation.setMaxParallelism(1);
		nonParallel = true;
		return this;
	}
@ PublicEvolving public SingleOutputStreamOperator < T > forceNonParallel ( ) { transformation . setParallelism ( 1 ) ; transformation . setMaxParallelism ( 1 ) ; nonParallel = true ; return this ; }
Sets the parallelism and maximum parallelism of this operator to one.
And mark this operator cannot set a non-1 degree of parallelism.

@return The operator with only one parallelism.