Table of Contents
- 1 Can we store object in HashMap?
- 2 Can we use employee class as key in HashMap?
- 3 Can you store an array in a Hashtable?
- 4 Can we store custom object as key in HashMap?
- 5 Does HashMap store key?
- 6 What is the difference between Hashtable and HashMap in Java?
- 7 How to use employee as a key in a hash based structure?
Can we store object in HashMap?
Internal working. All instances of Entry class are stored in an array declard as ‘transient Entry[] table’ . For each key-value to be stored in HashMap, a hash value is calculated using the key’s hash code. This hash value is used to calculate the index in the array for storing Entry object.
Can you store objects in Hashtable?
The Hashtable class implements a hash table, which maps keys to values. To successfully store and retrieve objects from a hashtable, the objects used as keys must implement the hashCode method and the equals method.
Can we use employee class as key in HashMap?
Answer to your question is yes, objects of custom classes can be used as a key in a HashMap.
Can we add employee object as key in HashMap?
Can you store an array in a Hashtable?
You can easily put them into a Hashtable of int -> float . The following method will use their index in the array as the key.
Which class can be used to store key value pairs?
Java HashMap class
Java HashMap class implements the Map interface which allows us to store key and value pair, where keys should be unique.
Can we store custom object as key in HashMap?
What will happen if you try to store null key in HashMap?
For HashMap, it allows one null key and there is a null check for keys, if the key is null then that element will be stored in a zero location in Entry array.
Does HashMap store key?
The basic idea of HashMap is this: A HashMap is really an array of special objects that hold both Key and Value. The array has some amount of buckets (slots), say 16. The hashing algorithm is provided by the hashCode() method that every object has.
What is the use of HashMap class?
* This class provides custom implementation of HashMap (without using java api’s)- which allows us to store data in key-value pair form. * insertion order of key-value pairs is not maintained.
What is the difference between Hashtable and HashMap in Java?
One object is used as a key (index) to another object (value). If you try to insert the duplicate key, it will replace the element of the corresponding key. HashMap is similar to HashTable, but it is unsynchronized. It allows to store the null keys as well, but there should be only one null key object and there can be any number of null values.
Why can’t I get the value of myemployee in a hashmap?
Employee is a mutable object. That will create problems with a HashMap. Let’s look at the code below: Once the Employee Object is mutated, the hashcode of that object is going to change. Now, if we try to retrieve it in step 3 (with the different hashcode), it will go to a different bucket and not be able to get the value.
How to use employee as a key in a hash based structure?
Now we can use Employee as a key in a Hash based structures. We can create HashSet and HashMap: Going further to the source code of the HashSet – we see that it actually use a HashMap inside and add our values as a HashMap’s keys with a dummy internal object as each Map’s entry value, check the constructor and add method: