Collections.max function is returning hashcodes (I think)

Collections.max function is returning hashcodes (I think)

By : faisalalicpy
Date : November 22 2020, 10:38 AM
help you fix your problem System.out.println(maxTree);calls toString() on maxTree. Since you did not override it, it calls the method on Object, which just outputs the full class name and some additional information.
You need to implement toString()yourself to get an more readable output.
code :
public class Tree {
    public double suitability = Math.random();
    public int id;
    public static int count = 1;

    public Tree(double suitability, int id) {
        this.id = count;

    public double getSuit() {
        return suitability;

    public void setSuit(double suitability) {
        this.suitability = suitability;

    public void measureSuit() {
        System.out.println("Tree number " + id + " has a suitability of " + suitability);

    public String toString() {
        return "I am the tree with id " + id;

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Java Hashtable .containsKey(String key) is returning true even when the strings and hashcodes are different... How?

Java Hashtable .containsKey(String key) is returning true even when the strings and hashcodes are different... How?

By : user2946601
Date : March 29 2020, 07:55 AM
I wish this help you I've reread your question, and as I understand it you have the following problem:
You do
code :
bol.put(somePuzzle.key, somePuzzle)
How hashcodes for enums are calculated in Java, and combining enum hashCodes for a HashMap's key

How hashcodes for enums are calculated in Java, and combining enum hashCodes for a HashMap's key

By : Big Al
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further Yes, you are right in that the hashcode of an enum element will come from the static instance, bound to memory positions, and be unique.
On the other hand, there are better ways of generating a hashcode with less collision probability. Check out, for example, the defaults that eclipse can autogenerate for you (right click, Source> Generate hashCode and equals)
code :
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((enum1 == null) ? 0 : enum1.hashCode());
    result = prime * result + ((enum2 == null) ? 0 : enum2.hashCode());
    return result;
VersionControlServer.QueryHistory returning System.Collections.IEnumerable / System.Collections.Generic.IEnumerable

VersionControlServer.QueryHistory returning System.Collections.IEnumerable / System.Collections.Generic.IEnumerable

By : Orlando Fernando Mar
Date : March 29 2020, 07:55 AM
I wish this helpful for you If you're sure the collection only contains ChangeSet items you can use the Linq extension method Cast():
code :
IEnumerable myCollection = ...
IEnumerable<ChangeSet> myGenericCollection = myCollection.Cast<ChangeSet>();
IEnumerable myCollection = ...
IEnumerable<ChangeSet> myGenericCollection = myCollection.OfType<ChangeSet>();
Objects.hash returning different hashCodes for equal objects

Objects.hash returning different hashCodes for equal objects

By : user3643350
Date : March 29 2020, 07:55 AM
This might help you As you noted, if objects A and B are equal (in the sense that A.equals(B) returns true, they should have the same hash code. By extension, if you implement your equals method by checking the equality of a series of fields, using Objects.hash should provide a proper hashcode.
But this isn't what you're doing here - you're using Arrays.equals to compare two arrays - as you should. Arrays with the same contents are not equal, and thus may (and probably will) have different hash codes. Instead, you can use Arrays#hashCode to get value's hash code:
code :
public int hashCode() {
    return Objects.hash(owner, Arrays.hashCode(value));
    // Here -------------------^
Collections.sort Hashcodes

Collections.sort Hashcodes

By : quinn
Date : March 29 2020, 07:55 AM
I hope this helps . A List is an ordered collection. This means that a List with [1, 2] is not equal to a List [2, 1] nor should the hashCode() be the same (ideally)
When you sort the collection you change it's order and thus it's hashCode. Note this is not guarenteed for all types. e.g. all Long of the formula ((x + y) & 0xFFFFFFFF) + y << 32) have the same hashCode for the same value of x. This means you have a list of Long where each long has the same hashCode and thus the list of these numbers will have the same hashCode regardless of order.
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