Sainmhíníonn an bheirt conas rudaí a ordú, ach ar dhifferent slí: sainmhíníonn Comparable ord nádúrtha aicme (curtha i bhfeidhm ag an aicme féin), agus sainmhíníonn Comparator ord agus malartach (réad ar leithligh). Braitheann an rogha ar cibé an bhfuil an t-ord intreach nó bunaithe ar chás.
public class Person implements Comparable<Person> {
private String name;
private int age;
@Override
public int compareTo(Person other) { // defines THE natural order
return Integer.compare(this.age, other.age); // by age
}
// return: negative if this < other, 0 if equal, positive if this > other
}
List<Person> people = ...;
Collections.sort(people); // uses compareTo — sorts by age (the natural order)
Taistíonn Comparable istigh san aicme trí compareTo(), ag sainmhíniú a aon ord réamhshocraithe. Úsáideadh go huathoibríoch ag Collections.sort, TreeSet, TreeMap, etc.
// define orderings OUTSIDE the class — as many as you need
Comparator<Person> byName = (a, b) -> a.getName().compareTo(b.getName());
Comparator<Person> byAge = Comparator.comparingInt(Person::getAge);
people.sort(byName); // sort by name
people.sort(byAge.reversed()); // by age, descending
Comparator is réad ar leithligh a thú, ag ligean duit iolra ordanna éagsúla a sainmhíniú don aicme céanna gan a modhnú.
Comparator<Person> comp = Comparator
.comparing(Person::getLastName) // primary: last name
.thenComparing(Person::getFirstName) // tie-break: first name
.thenComparingInt(Person::getAge) // then: age
.reversed(); // reverse the whole thing
people.sort(comp);
Déanann na modhanna comparing/thenComparing ar stíl tógálaí an sórtáil ilréimse casta gonta agus inléite.
Comparable → the class has ONE obvious natural order (numbers by value, strings
alphabetically, dates chronologically); you own the class
Comparator → you need MULTIPLE orderings, situational/custom ordering, OR you
can't modify the class (e.g. sorting a third-party type differently)
Is gá go leanúnach rudaí a ordú — liostaí a sórtáil, TreeSet/TreeMap a úsáid, íosmhéid/uasmhéid a aimsiú.
Tuigint an idirdhealaithe Comparable-vs-Comparator a thabhairt duit rogha a dhéanamh i gceart: Comparable d'ord intreach aonair aicme (ionsuite, úsáidte réamhshocraithe), Comparator don fhoscairt a bheith ag iolra ordanna nó ordanna seachtracha (na sonraí céanna a sórtáil de réir réimsí éagsúla, nó a ordú na cineálacha nach bhfuil smacht agat orthu).
Déanann an API Comparator foluain nua-aimseartha (comparing/thenComparing/reversed) an sórtáil ilthérmach galánta.
A bheith ábalta ar an dá cheann — agus cathain a thagann gach ceann — ríthábhachtach do bhheith ag obair le struchtúir sonraí sórtáilte agus is topaic dheasghnátha phraiticiúil agus agallamh é i Java.