Java Essentials - Hash map in java

HashMap in Java

What is HashMap? HashMap uses hash table and implements the map interface

And there are some basic differences between this hash table and also the hash map

So let us go for some further discussion on it. The HashMap in Java collection

The HashMap class uses a hash table to implement the map interface

And this allows the execution time of basic operations, such as your gates put to remain constant even for large data sets

And that is one of the advantages. And also, it also takes key value paired like our hash table and to store data into the map

So that means in our previous discussion, we have discussed that hash table stores the value

in the form of key value pair. And same thing will be followed here in case of hash map

and to store data onto the map in this case. The main differences between the hash table and hash map are, so point number one

hash map is not thread safe and not synchronized, but hash tables are threat safe

So that's why for the multi-threated environment, it is our suggestion to use these hash tables

Next one is that hash map can accept one null value, but hash table does not support null values

So that is another difference between this hash map and hash table So let us go for some practical demonstration to show you that how this hash map can be implemented can be used in our Java code

So here is the demonstration for you. In this program, we are discussing hash map and hash map objects

Now, what is the hash map? So here you can find that hash table based implementation of the map interface

And this implementation provides all of the option. map operations and permits null values and the null key the hash map class is

roughly equivalent to the hash table except that it is unsynchronized and permits

null but in case of hash table we didn't allow to insert any null key or the null

values but here in case of hash map the null values and the null keys are permitted

this class makes no guarantee as to the order of the map in

particular it does not guarantee that the order will remain constant constant

over the time also so let us go for one hash map object the name of the object

is employee hash it has got instantiated it will be holding this integer

wrapper class object as the key and string object as the value here so how to

add item to this hash map object the method is put so here the key is 12 and

the value is programmer key is 14 values instructor in this way we have added

five such values there so if we print this employee hash then what will be the outcome you can easily find that so the employee hash map will be having the value that is 18 tester 21 is equal to casual 12 is equal to programmer 13 is equal to programmer and 14 is

equal to instructed you see the order in which I added I put all these items

so they are not occurring in the same order and also you can find that the

value has got repeated but the key cannot get repeated here you see the value has got repeated so here we are having

this programmer here also are having this programmer but the key values are

different here so if you go for another one say if I put this one say for this

12 for this 21 rather I'm putting this one as debugger

so you can find that this 21 has got updated with the text debugger here so let us let us go so it is

my debugger so I'm changing the spelling here actually so that you see 21 is

now debugger so what is happening as the key values key are the same so that's

why the debugger is not a new item for this employee hash but this 21 the

respective value casual has got replaced and updated by the value debugger here so if it is this line and if you go on executing we can find that against this by 21 key the value is casual now see we going to search how to how to

search a particular item against the key so if employee has dot contents key

18 so you see 18 is present so that's why the true will be the outcome you can see the

contents key is returns bullion contents key returns bullion and it is under the

package Java dot util under the class hash map contents key is the respective

method name which will take one object as input argument object key as input

argument here we have passed this integer class wrapper class object 18 as input argument and it returns bullion to check whether the value the key

has been found there or not so in case of 18 the type of the employee

there is a system dot out of print talent the type of the employee will be employee has got

get 18 you can easily find that it is printing tester because against 18 we're

having the value tester here so tested is getting printed but what about this

108 so 108 is this respective key is not present here so it will go on

printing the key is not found so in this way in this particular demonstration

we have discussed into details with the demonstration and the sample programming

code hash map its concept and how to define objects and how to define and how to access

different methods from this object as well thanks for watching this video