Learning lambda expressions encountered in the pit

A recent study using java8 lambda expressions. According to the literal meaning of the method, it is easy to understand and use to get started.

But recently encountered when using a lambda expression problem, code logic without any problems, but the result is not satisfactory.

First the old code:

testOneList.stream().distinct().filter(item ->

　　!testTowList.stream().map(TestTwoModel::getCode).collect(Collectors.toList()).contains(item)

).map(item -> testTwoList.add(new TestTwoModel(item,.....)));

I began to wonder if I am using the wrong method, so do not use this method? Yeah unreasonable. Search the Internet for a long time, continuous testing and commissioning, we did not find the problem.

 

Finally, request the great God, we will see to the mistake. Read:

testOneList.stream().distinct().filter(item ->

　　!testTowList.stream().map(TestTwoModel::getCode).collect(Collectors.toList()).contains(item)

).forEach(item -> testTwoList.add(new TestTwoModel(item,.....)));

 

map itself is not an end point, placed at the end it will be ignored, and we wanted to change forEach or later add collect will work.