hashset

My Custom class that will be contained by HashSet public class Person { String name; int age; public Person(String name, int age) { this.name = name; this.age = age; } @Override public String toString() { return "Person{" + "hashcode='" + this.hashCode() + '\'' + "name='" + name + '\'' + ", age=" + age + '}'; } @Override public boolean equals(Object o) { if (this == o) return true; if (!(o instanceof Person)) return false; Person person = (Person) o; if (age != person.age) return false; if (!name.equals(person.name)) return false; return true; } @Override public int hashCode() { int result =

I've got a HashSet<Integer> with a bunch of Integers in it. I want to turn it into an array, but calling hashset.toArray(); returns an Object[] . Is there a better way to cast it to an array of int other than iterating through every element manually? I want to pass the array to void doSomething(int[] arr) which won't accept the Object[] array, even if I try casting it like doSomething((int[]) hashSet.toArray()); Matthew Flaschen Apache's ArrayUtils has this (it still iterates behind the scenes ): doSomething(ArrayUtils.toPrimitive(hashset.toArray())); They're always a good place to check for

For lists, we use the Collections.sort(List) method. What if we want to sort a HashSet ? isak gilbert A HashSet does not guarantee any order of its elements. If you need this guarantee, consider using a TreeSet to hold your elements. However if you just need your elements sorted for this one occurrence, then just temporarily create a List and sort that: Set<?> yourHashSet = new HashSet<>(); ... List<?> sortedList = new ArrayList<>(yourHashSet); Collections.sort(sortedList); Add all your objects to the TreeSet , you will get a sorted Set. Below is a raw example. HashSet myHashSet = new HashSet(

I have been trying to understand the internal implementation of java.util.HashMap and java.util.HashSet . Following are the doubts popping in my mind for a while: Whats is the importance of the @Override public int hashcode() in a HashMap/HashSet? Where is this hash code used internally? I have generally seen the key of the HashMap be a String like myMap<String,Object> . Can I map the values against someObject (instead of String) like myMap<someObject, Object> ? What all contracts do I need to obey for this happen successfully? Thanks in advance ! EDIT: Are we saying that the hash code of the

As a result of another question I asked here I want to use a HashSet for my objects I will create objects containing a string and a reference to its owner. public class Synonym { private string name; private Stock owner; public Stock(string NameSynonym, Stock stock) { name=NameSynonym; owner=stock } // [+ 'get' for 'name' and 'owner'] } I understand I need a comparer , but never used it before. Should I create a separate class? like: public class SynonymComparer : IComparer<Synonym> { public int Compare(Synonym One, Synonym Two) { // Should I test if 'One == null' or 'Two == null' ???? return