May 1, 2024
March 10, 2022
Comparable (Java SE 21 & JDK 21) with Examples.
You will find code examples on most Comparable<T> methods.
Summary
This interface imposes a total ordering on the objects of each class that implements it. This ordering is referred to as the class's natural ordering, and the class's compareTo method is referred to as its natural comparison method.
See also : Comparator
// The String class implements the Comparable interface.
final Comparable<String> comparable = "bbb";
System.out.println(comparable.compareTo("aaa")); // 1
System.out.println(comparable.compareTo("bbb")); // 0
System.out.println(comparable.compareTo("ccc")); // -1
final var list = List.of("ddd", "bbb", "ccc", "aaa");
System.out.println(list); // [ddd, bbb, ccc, aaa]
final var sorted = list.stream().sorted().toList();
System.out.println(sorted); // [aaa, bbb, ccc, ddd]
Methods
int compareTo (T o)
Compares this object with the specified object for order.
// The String class implements the Comparable interface.
final var list = List.of("ddd", "bbb", "ccc", "aaa");
System.out.println(list); // [ddd, bbb, ccc, aaa]
final var sorted = list.stream().sorted().toList();
System.out.println(sorted); // [aaa, bbb, ccc, ddd]
record Sample(String text, int num) implements Comparable<Sample> {
@Override
public String toString() {
return "(%s, %d)".formatted(text, num);
}
@Override
public int compareTo(Sample o) {
if (!text.equals(o.text())) {
return text.compareTo(o.text());
} else {
return num - o.num();
}
}
}
final var list = List.of(
new Sample("bbb", 2), new Sample("bbb", 3), new Sample("bbb", 1),
new Sample("aaa", 3), new Sample("aaa", 1), new Sample("aaa", 2)
);
// [(bbb, 2), (bbb, 3), (bbb, 1), (aaa, 3), (aaa, 1), (aaa, 2)]
System.out.println(list);
final var sorted = list.stream().sorted().toList();
// [(aaa, 1), (aaa, 2), (aaa, 3), (bbb, 1), (bbb, 2), (bbb, 3)]
System.out.println(sorted);