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OK we're not done with the collection hierarchy.

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Now it's time to look at the map hierarchy which is a second inheritance tree in the collections framework

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.

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Let's begin by looking at the map interface which is the root of the map hierarchy.

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We pretty much discuss all of these points during our discussion on hash table.

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But let's quickly glanced through them once again not a map store key value pairs and they're useful

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for Fras lookups.

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Biccies IMAP implementation like a hash map is also referred to as an associate the way maps can not

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have duplicate IIS but duplicate values are fine on each key maps to at most one value not some map

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implementations allow only one Halki while others do not allow any Nalco at all.

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Similarly null values may be allowed or they may be prohibited.

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One of the like in the case of collection map also comes with a skeletal implementation abstract map

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.

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So limitations like hash map extend this particular class just know that it's not just map collection

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interfaces which come with skeletally implementations even list certain new interfaces.

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Also combat's little implementations under also appropriately named as abstract list abstract set an

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abstract Q On all three of them.

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Extend that abstract collection.

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And here is the declaration of map interface similar to collection and office.

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This interface also has methods which are classified and do basic operations on bulk operations collection

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interface.

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Also how are the operations and we don't how anything of that sort in the map interface.

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But map has something called collection view operations and B-ble will soon we'll get them look at Unlike

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collection map interface does not extend the interface but the elements can still be detected and we

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will see how that can be done.

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And here are the methods which follow the basic operations.

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Not that here the genetics notation involves the letters K and the V K would stand for key while before

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value but don't bother about them as we still did not discuss genetics.

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But we know that Canvey can represent anything.

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Right.

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So that's what genetics is about.

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And that anything will be specified at the object creation.

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That is when we are creating an instance of a particular map implementation on the first method.

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Here is the put method.

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It simply asks that given key and value pair into the map.

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If there is already a mapping with the same key then the value in that mapping will be overwritten with

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the new value.

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We already discussed it when covering hash table.

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Also the old value will be returned by the matter.

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So that's the reason the written type for this method is V where we would be the all value.

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But if there was no mapping with that key then the new mapping will be inserted and the null value will

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be returned.

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But if the map implementation allows it not you.

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And there is a matching key with a null value then the null value would be written.

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So in this case we cannot tell whether the null value that was written was due to inserting an entirely

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new mapping or if it was due to overwriting an existing mapping which had a null value.

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But to distinguish these two cases we can invoke the Kandinsky method which returns a true if the input

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key is present in the map.

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Next is the get method.

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Undertreatment the value corresponding by a given key.

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If there is no mapping with that key then a null is written the moment that would remove the mapping

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for a key under a corresponding value attribute in a null.

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If the mapping with a matching key was not for it it is because contains key convinced volume that would

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return true if the map contains the specified value size would read and the size of the map is empty

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.

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Would return true if the size of the map is zero which means that it is empty.

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And here are the bulk operations.

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Put all method what are all the mappings from the input map into the current map.

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So it is similar to the idle method in the collection interface and cleared matter.

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Simply remove all the mappings from the map.

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Even the collection interface had an identical method and he had a collection view operations you would

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use the first method.

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He said if you want to view all the keys present in the map.

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So this method would it an asset.

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If you want to remove one element from the ribbon set you can invoke the return method on the return

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set and then you can invoke the remote method on the return to do it.

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Alternatively we can also use set methods like Rimmel.

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Remove all retain all and clear.

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However you cannot work either add or are all methods and you will get an unsupported operation exception

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.

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If you invoke these matters not that the return set is bad but the origin Alima.

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So any changes made in the returns it will be reflected in the original map and vice versa.

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Next is a values motard and it will return a collection view of all the values in the map on all the

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properties we just discussed.

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For the keyset method will also apply for this method.

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Note that in case of keyset a set was written whereas in this case a collection is being written.

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And can you guess the reason for that.

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It is just because Keys are unique and so a set is returned the rest values can contain duplicate and

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hence a collection is written.

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Not a third method and Chrisette is an interesting method and it can be used for creating them up.

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It returns a set view of all the mappings in the map on each mapping is an instance of this interface

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called entry which is a nested interface within the map interface so it is not just a process but we

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can also how interfaces as an interface is a nice thing about such a nested interface is that it improves

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the readability.

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No how did been a separate individual interface served as a separate file.

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Then it would unnecessarily pollute the namespace even though it is used only by MAP implementations

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.

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So someone looking at this package might do.

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HUME That angry interface is very widely used but now in this case since it is part of the map interface

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one would assume that it has something to do with only maps.

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Now here each instance of entry corresponds to a mapping in MAP unsoiled stores both he as well as value

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on hence pro-white my thoughts like get it and get value.

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So any derating them up these methods can be invoked.

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There is also the set value method which can be used to update the value in a particular mapping.

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Anyway we were tested.

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In the next question.

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When we look at hash map just know that like the other two collection will return the set that is returned

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.

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But this particular method is backed by the original map and so all properties with regards to making

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any changes will also apply here.

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Finally just note that you should be very careful if the keys you use are immutable.

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You would want to use keys which are immutable like the strings.

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The reason is if you start a mutable object esky and then later you change the state of the object.

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Then when you search for that same key the map method and a null value for instance if the map is a

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hash map then the hash function might give a different index value.

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That is the bucket number after the object stood was changed.

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That is the hash function so logic is dependent on the objects state.

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Even if it was the same bucket number the subsequent equals method might see that no matching mapping

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was found in the corresponding linked list.

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Anyway Robert does this out later in the demo.

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So let's not worry if it's not really clear to you.

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So that's up with the map interface in the next lesson.

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They will look at hash map and maybe just all the matters that we have seen in this lesson.

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So just state your own and it's going to be an interesting them.

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Thank you