ch07_comparators

7. Comparators

Related interfaces

• Comparator - int Comparator<T>#compare(T, T)
• Comparable - int Comparable<T>#compareTo(T)

Collection sorting before Java 8

• with util class Collections -> methods Collections#sort
  • void sort(List) - list entities must implement Comparable
  • void sort(List, Comparator) - list entities not need implement Comparable because the second argument is Comparator

Collection sorting since Java 8

• exists method void List#sort(Comparator)
• Stream API provides the (stateful intermediate) operation Stream Stream#sorted(Comparator)
• in both cases the input Comparator is possible to write as lambda expression
  • or better way is use the Comparator#comparing - see bellow

Comparator#comparing

• are new static methods since Java 8
• provides great objects comparing support and better usage in Streams
• is possible to write as method reference
• existing methods are:
  • Comparator#comparing(Function)
  • Comparator#comparing(Function, Comparator)
  • Comparator#comparing(ToIntFunction) - ToLongFunction or ToDoubleFunction can be used instead of ToIntFunction
• is possible to write more complex comparison expressions in combination with methods:
  • thenComparing(Comparator)
  • thenComparing(Function)
  • thenComparing(Function, Comparator)
  • reversed()