comparable

What is the difference between returning 0 , returning 1 and returning -1 in compareTo() in Java? Official Definition From the reference docs of Comparable.compareTo(T) : Compares this object with the specified object for order. Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object. The implementor must ensure sgn(x.compareTo(y)) == -sgn(y.compareTo(x)) for all x and y. (This implies that x.compareTo(y) must throw an exception iff y.compareTo(x) throws an exception.) The implementor must also ensure that the relation

I am trying to sort List of employees by name then age using Java8 Comparator , I have created below Comparator but it gives me a compiler error Type mismatch: cannot convert from Comparator<Object> to <unknown> Comparator<String> c = Comparator.comparing(s -> s.split("\\s+")[0]) .thenComparingInt(s -> Integer.parseInt(s.split("\\s+")[1])); //compile error but it works if I explicitly specify the Type Comparator<String> c = Comparator.<String, String> comparing(s -> s.split("\\s+")[0]) .thenComparingInt(s -> Integer.parseInt(s.split("\\s+")[1])); //works or by creating two Compartor s and

I have this code: package org.optimization.geneticAlgorithm; import org.optimization.geneticAlgorithm.selection.Pair; public abstract class Chromosome implements Comparable<Chromosome> { public abstract double fitness(); public abstract Pair<Chromosome> crossover(Chromosome parent); public abstract void mutation(); public int compareTo(Chromosome o) { int rv = 0; if (this.fitness() > o.fitness()) { rv = -1; } else if (this.fitness() < o.fitness()) { rv = 1; } return rv; } } And every time I run this code I get this error: Exception in thread "main" java.lang.IllegalArgumentException:

What is the standard way of making a class comparable in Python 3? (For example, by id.) For a full set of comparison functions I have used the following mixin, which you could put in say for example a mixin.py in your module. class ComparableMixin(object): def _compare(self, other, method): try: return method(self._cmpkey(), other._cmpkey()) except (AttributeError, TypeError): # _cmpkey not implemented, or return different type, # so I can't compare with "other". return NotImplemented def __lt__(self, other): return self._compare(other, lambda s, o: s < o) def __le__(self, other): return self

If I implement java.lang.Comparable for a class, do I still have to override the equals() method? Or will the Comparable work for equals as well? If the answer is no , then what if some discrepancy arises? Let's say the way I term two objects as equal within the equals() method is different from the way I term two objects of the same class as equal within the compareTo() of the Comparable . Moreover, if I implement Comparable , do I also have to override equals() ? While it is recommended (and pretty sensible) that having a.compareTo(b) == 0 imply that a.equals(b) (and visa versa), it is not

An enum in Java implements the Comparable interface. It would have been nice to override Comparable 's compareTo method, but here it's marked as final. The default natural order on Enum 's compareTo is the listed order. Does anyone know why a Java enums have this restriction? For consistency I guess... when you see an enum type, you know for a fact that its natural ordering is the order in which the constants are declared. To workaround this, you can easily create your own Comparator<MyEnum> and use it whenever you need a different ordering: enum MyEnum { DOG("woof"), CAT("meow"); String sound

If I have a list of elements I would like to sort, Java offers two ways to go about this. For example, lets say I have a list of Movie objects and I’d like to sort them by title. One way I could do this is by calling the one-argument version of the static java.util.Collections.sort( ) method with my movie list as the single argument. So I would call Collections.sort(myMovieList). In order for this to work, the Movie class would have to be declared to implement the java.lang.Comparable interface, and the required method compareTo( ) would have to be implemented inside this class. Another way to