This should work for all classes that extend Number, and are Comparable to themselves. By adding the & Comparable you allow to remove all the type checks and provides runtime type checks and error throwing for free when compared to Sarmun answer. class NumberComparator<T extends Number & Comparable> implements Comparator<T> { public int compare( T … Read more
It’s worth mentioning that the following expression: new Long(10).equals(new Integer(10)) is always false, which tends to trip everyone up at some point or another. So not only can you not compare arbitrary Numbers but you can’t even determine if they’re equal or not. Also, with the real primitive types (float, double), determining if two values … Read more
Java needs to know a type of all variables. In many lambdas it can infer a type, but in your first code snippet, it cannot guess the type of s. I think the standard way to solve that problem would be to declare it explicitly: Comparator<String> c = Comparator.comparing((String s) -> s.split(“\\s+”)[0]) .thenComparingInt(s -> Integer.parseInt(s.split(“\\s+”)[1])); … Read more
This is the right way to compare strings: int studentCompare = this.lastName.compareTo(s.getLastName()); This won’t even compile: if (this.getLastName() < s.getLastName()) Use if (this.getLastName().compareTo(s.getLastName()) < 0) instead. So to compare fist/last name order you need: int d = getFirstName().compareTo(s.getFirstName()); if (d == 0) d = getLastName().compareTo(s.getLastName()); return d;
Guava is more elegant: return ComparisonChain.start() .compare(d1.weight, d2.weight) .compare(d1.age, d2.age) .compare(d1.name, d2.name) .result(); Apache commons-lang has a similar construct, CompareToBuilder.
Use Comparable if you want to define a default (natural) ordering behaviour of the object in question, a common practice is to use a technical or natural (database?) identifier of the object for this. Use Comparator if you want to define an external controllable ordering behaviour, this can override the default ordering behaviour.
You just have to define that Animal implements Comparable<Animal> i.e. public class Animal implements Comparable<Animal>. And then you have to implement the compareTo(Animal other) method that way you like it. @Override public int compareTo(Animal other) { return Integer.compare(this.year_discovered, other.year_discovered); } Using this implementation of compareTo, animals with a higher year_discovered will get ordered higher. I … Read more
When your class implements Comparable, the compareTo method of the class is defining the “natural” ordering of that object. That method is contractually obligated (though not demanded) to be in line with other methods on that object, such as a 0 should always be returned for objects when the .equals() comparisons return true. A Comparator … Read more
The text below comes from Comparator vs Comparable Comparable A comparable object is capable of comparing itself with another object. The class itself must implements the java.lang.Comparable interface in order to be able to compare its instances. Comparator A comparator object is capable of comparing two different objects. The class is not comparing its instances, … Read more
> is a numerical comparison operator, and according to JLS Sec 15.20.1: The type of each of the operands of a numerical comparison operator must be a type that is convertible (ยง5.1.8) to a primitive numeric type, or a compile-time error occurs. Your Time type cannot be converted to a primitive numeric type, because it’s … Read more