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| Tags/Keywords : key-and-value-pair - Composite-keys-in-Hashtable - Coding-Tips-on-Java Example
Author : Amit
Date (Year/Month/Date): 2009-01-25
Using Composite keys in Hashtable in Java Technology | | | | |
|
Some of the data structures
implemented in Java Technology,
such as Hashtable, HashMap,
takes key and value as Serializable
Object, if Hashtable is to be
persisted out of JVM environment.
Key to this Hashtable is stored as
value, not as instance reference.
It is always easy to use a String
object as key, but if requirements
is to provide multiple Java type as key.
Suppose key to Hashtable is composed
of multiple fields like
String name
int age
boolean status
|
How is it possible?
Any guesses!!!
Yes, it is possible, by defining a user defined class with these fields
and main thing is to override equals and hashCode method, so that
object identity can be defined as follows:
public boolean equals(Object obj)
{
if( this.name != null && this.name.equals(((CompositeKeys)obj).name)
&& this.phone == ((CompositeKeys)obj).phone && this.status ==
((CompositeKeys)obj).status)
return true;
else
return false;
}
public int hashCode()
{
return (name+""+phone+""+status).hashCode();
}
equals method returns true or false depending on the values of these fields.
hashCode method returns hash value based on the field values.
If all the field values for different objects are same, then it makes key
for Hashtable as same.
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Commented By ->
kalpana | I want to add a value to hashtable in java at runtime.For eg.,If my table alredy contains 5 values i want to
add the new element as the sixth one
Looking forward for your answer
Thanks in advance |
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