Sorting using comparator interface and Java 8 streams

Question

Below is my code to sort resultSet based on two-parent attributes(Attribute 1 and attribute 2)

Comparator<Parent> byFirst = (e1, e2) -> e2.getAttrib1().compareTo(e1.getAttrib1());

Comparator<Parent> bySecond = (e1, e2) -> e1.getAttrib2().compareTo(e2.getAttrib2());

Comparator<Parent> byThird = byFirst.thenComparing(bySecond);

 

List<Parent> sortedList = resultSet.stream().sorted(byThird).collect(Collectors.toList());

Can anyone tell me how to sort the parentlist on the basis of attributes from the Child class and GrandChild class? 

Answer 1

You can use Comparator.comparing which makes comparators for any attributes which you want to compare. Check out the code below: 

Comparator<Parent> byAttr1ofFirstChild = Comparator.comparing(

    parent -> parent.getChildren().get(0).getAttr1()

);

Comparator<Parent> byAttr1ofFirstGrandChild = Comparator.comparing(

    parent -> parent.getChildren().get(0).getGrandChildren().get(0).getAttr1()

);

 

List<Parent> sortedList = parents.stream()

    .sorted(byAttr1ofFirstChild.thenComparing(byAttr1ofFirstGrandChild))

    .collect(toList());

Comparator.comparing helps you use static imports to code efficiently : 

Comparator<Parent> byFirst = comparing(Parent::getAttrib1, reverseOrder());

Comparator<Parent> bySecond = comparing(Parent::getAttrib2);

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