hashset

Have the following class: public class Member { private int x; private long y; private double d; public Member(int x, long y, double d) { this.x = x; this.y = y; this.d = d; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + x; result = (int) (prime * result + y); result = (int) (prime * result + Double.doubleToLongBits(d)); return result; } @Override public boolean equals(Object obj) { if (this == obj) { return true; } if (obj instanceof Member) { Member other = (Member) obj; return other.x == x && other.y == y && Double.compare(d, other.d) ==

Looking at the source of Java 6, HashSet<E> is actually implemented using HashMap<E,Object> , using dummy object instance on every entry of the Set. I think that wastes 4 byte (on 32-bit machines) for the size of the entry itself. But, why is it still used? Is there any reason to use it besides making it easier to maintain the codes? JXG Actually, it's not just HashSet . All implementations of the Set interface in Java 6 are based on an underlying Map . This is not a requirement; it's just the way the implementation is. You can see for yourself by checking out the documentation for the various

I have implemented a method which simply loops around a set of CSV files that contain data on a number of different module. This then adds the 'moduleName' into a hashSet. (Code shown below) I have used a hashSet as it guarantees no duplicates are inserted instead of an ArrayList which would have to use the contain() method and iterate through the list to check if it is already there. I believe using the hash set has a better performance than an array list. Am I correct in stating that? Also, can somebody explain to me: How to work the performance for each data structure if used? What is the

Why do the second and third sets preserve order: Integer[] j = new Integer[]{3,4,5,6,7,8,9}; LinkedHashSet<Integer> i = new LinkedHashSet<Integer>(); Collections.addAll(i,j); System.out.println(i); HashSet<Integer> hi = new HashSet<Integer>(i); System.out.println(hi); LinkedHashSet<Integer> o = new LinkedHashSet<Integer>(hi); System.out.println(o); Here's the output I get: 3,4,5,6,7,8,9 3,4,5,6,7,8,9 3,4,5,6,7,8,9 Behrang The second one (just using HashSet ) is only a coincidence. From the JavaDocs : This class implements the Set interface, backed by a hash table (actually a HashMap instance).