Help need to know hashcode() and Equals method

Hi ,
Now i'm working under hashtable functions. In that all are asking me to overwrite hashCode and equals method. Why?
Please let me know briefly...........

jverd wrote:
euph wrote:
jverd wrote:
euph wrote:
REFTY5_ wrote:
Hi ,
Now i'm working under hashtable functions. In that all are asking me to overwrite hashCode and equals method. Why?
Please let me know briefly...........Thery're asking you to override the equals and hashCode methods. Override means replace.So does "overwrite." However, as you point out, "override" is the correct word here.So you think "overwrite" means the same as "replace"?To the same extent that "override" does. But both are in the general sense. Override has a specific meaning in this Java context, and overwrite does not.Don't tell me. That's what I said in my original reply.
To my ear it doesn't. To me "overwrite" means the original is destroyed, whereas when something is "replaced" the fate of the original is unknown. So I think there's a slight semantic difference between these words.Fair enough.Fair enougth, but the next time I suggest you're better sorted.

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When we override Hashcode and Equal Methods

Hi....I have doubt regading Hashcode and equal methods
why we override this two methods....
why we override hashcode method when we are overriding equal method,
i would very thankful to give answser
Thank you
Ramesh

hash code is computed to check the equality of two
objects ,
that is why if u change the default equal method
implementation , u need to change the hashcode method
as well.That's an incomplete answer at best.
The hashcode method is used by hashing algorithms and data strcutures such as HashMap. This value is used to determine what 'bucket' the reference will go into. It cannot, by itself determine equality.
If you are still unsure, I suggest looking up 'hash table' on google. I'm sure there's a decent explanation on wikipedia.

Why do we need to override Hascode and Equals method?

Hi,
== checks if the two references are equal and .equlas will check if the value is same, if we want .equals to take care of both reference and value are correct. why cant I just override equals with an extra check that references are equal(==).
Please someone elaborate on this and also tell me what role hashcode plays in this.
thanks
Anirudh

anirudh1983 wrote:
if we want .equals to take care of both reference and value are correct. why cant I just override equals with an extra check that references are equal(==).Many equals() methods do run an '==' check first for efficiency (and I would recommend it if you're writing one yourself).
Please someone elaborate on this and also tell me what role hashcode plays in this.The reason that it is good practise to override equals() and hashCode() together is to maintain consistency.
Hashcodes are used by all Java collections that contain the word 'Hash' in their name, and may also be used by other programs that need a hash code for identification; so if you supply one, you must follow the rules (which you can find in the API for Object.equals() and Object.hashCode()).
The main rule is this: *objects that are equal() must have equal hashcodes*.
Note that the reverse is NOT true: objects that are not equal() do not have to have different hashcodes, but it is usually better if they do.
There is quite a lot to know about hashcodes, and what makes a good one, so I suggest you follow dcminter's advice if you want to be a happy and prosperous Java programmer.
Winston

Use of hashCode and equals method in java(Object class)

What is the use of hashCode and in which scenario it can be used?similarly use of equals method in a class when it overides form Object class. i.e i have seen many scenario the above said method is overridden into the class.so why and in which scenario it has to override?Please help me.

You could find that out easily with google, that is a standard junior developer interview question.

Do I need to override enum's hashCode() and equals()?

Hi all:
I have a enum type let's say it is
public enum Type
ONE,
TWO;
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Type a = Type.ONE;
Type b = Type.TWO;should I use a.equals(b) or (a == b) If I want to use it as another class's key field, and I want to override this class hashCode() and equals() methods.
Can enum Type return the correctly hash code?
For example the class is like:
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pubilc boolean equals(Object other)
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Answered by the test code by myself.
We can use either equals or (==) to see if they are the same value.
The enum's hashCode() use System.identityHashCode() to generate the hashCode and they are always correct

Method Overriding-toString(),hashCode() and equals()?

Hi,
In some Java Classes, I saw that
toString()
hashCode()
equals()
these 3 methods of Object Class is overloaded.
I don't understand why and in what situation we have to override these 3 methods of Object Class.
Thanks in advance for ur Knowledge Sharing.
Regards,
S.Prabu

toString() is typically overridden in subclasses so as to output something useful about a class like instance variable values instead of just a hashvalue representing the object reference as per Object.
hashCode() and equals() are overridden typically for use within the collections framework though you need to fully understand the hashing contract before starting to override these as they can cause strange results if not overridden correctly.
Take a look at collections and specifically the hashing functionality of HashMap and HashSet for more info on these.

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Dear All,
Please let me know in which circumstances we write our own Hashcode method and equals method not the default one provided by java.Kindly give me complete code and scenario.
Thanks
Sumit

Thanks for your reply
I have one more question.
When equal method of Object class give the same result as equals we override then why should we override equals.For example see the below code
public class EqualsTest{
public EqualsTest() {
super();
public static void main(String[] args) {
Moof one =new Moof(8);
Moof two =new Moof(8);
if(one.equals(two))
System.out.println("one is equals to two");
class Moof {
private int moofvalue;
Moof(int val){
System.out.println("val inside moof constructor"+val);
moofvalue=val;
System.out.println("moofvalue inside moof constructor" +moofvalue);
public int getMoofValue()
System.out.println("moofvalue inside getmoffvalue method "+moofvalue);
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moofvalue inside moof constructor8
val inside moof constructor8
moofvalue inside moof constructor8
Object o in equalsMoof@119c082
moofvalue inside getmoffvalue method 8
true
one is equals to two
The last output "one is equals to two" gives the same result as overridng equals by us.So why should we override equals here.
Thanks
Sumit

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Help need to know hashcode() and Equals method

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