hashcode « HashMap « Java Collection Q&A

1. Double in HashMap    stackoverflow.com

I was thinking of using a Double as the key to a HashMap but I know floating point comparisons are unsafe, that got me thinking. Is the equals method on the ...

2. How should I implement this HashMap's equals and hashCode methods to represent an automaton state?    stackoverflow.com

I want to put State objects (which are HashMaps with Character as key and State as Value into an ArrayList named allStates. Should I override the equals and hashCode methods here? ...

3. Understanding the workings of equals and hashCode in a HashMap    stackoverflow.com

I have this test code:

import java.util.*;

class MapEQ {

  public static void main(String[] args) {
   Map<ToDos, String> m = new HashMap<ToDos, String>();
   ToDos t1 = new ToDos("Monday");
 ...

4. hashCode, implementation, and relation to HashMap    stackoverflow.com

So I asked another related question here: java string hash function with avalanche effect, but I have a different, related question now. What I established in that question was that the ...

5. Overriding equals() and hashCode() methods of HashMap implementation    stackoverflow.com

I have a hashmap of the type HashMap<Long, ArrayList<String>>. I need to override the equals() and hashCode() methods to gain in performance. What should be the overriding function like, for this ...

6. Testing / Profiling a hashcode function for java hashmap    stackoverflow.com

How do I test / profile a hashCode() implementation in Java? i.e. is it distributing my test data reasonably evenly etc? Is there any simple crude way in java API itself? ...

7. How does Java hashmap work?    stackoverflow.com

As per my understanding I think:

1. Its perfectly legal for two objects to have same hashcode.
2. If two objects are equal (using equals ) then they have same hashcode.
3. If two object are ...

8. Why does hashCode() return zero before items are added to HashMap?    stackoverflow.com

Map map = new HashMap();
System.out.println("hashCode:"+map.hashCode()); //hashcode==0 why?

map.put("test","test");
System.out.println("hashCode:"+map.hashCode()); //hashcode be okay here

9. If I override .equals(), do I need to override .hashCode() even if I don't use a HashMap?    stackoverflow.com

If I choose never to store my objects in the collection, do I need to override hashcode or can I have the same hashcode for my objects? Is it good or ...

10. StackOverflowError using hashCode() in HashMap in recursive method    coderanch.com

Hi everyone, OK, I'm really stumped here. I'm getting a StackOverflowError, which is occurring on the first line of my overridden hashCode() method of my POJO. hashCode() is being called from the get() method of HashMap, which is used in a recursive method. The map is not self-referential. Here's a snippet of hashCode(). public int hashCode() { final int PRIME = ...

11. how hashCode() is used in HashMap?    coderanch.com

12. Hashmap trying to understand hashCode(), equals(), get()    java-forums.org

Java Code: import java.util.*; class Dog{ public String name; public Dog(String n) { name = n; } public boolean equals(Object o){ System.out.println("i'm inside equals"); if((o instanceof Dog) && (((Dog)o).name == this.name)){ return true;} else{ return false;} } public int hashCode(){ return name.length(); } } public class MapTest { public static void main(String[] args) { Map m = new HashMap(); ...