HashMap Methods and its use

Question 1

1. What is the difference between remove (key) and remove(key, value ) pair?
2. What is the use of put, put all, remove(Key) and remove(Key value) , get(key), clear(), size(), isEmpty()., replace, replaceall().
3. Does collection have length or Size?

Answer 1

1. If we give remove (key) we will get the value in output.
   If we give remove(Key, value) we will get true .
2. 1Put() - Is used to add all the (Key, value) pair,
   after that in syso we can pass the reference object (hm) and print all the values
   2.Put all() - it a void return type it won’t return anything , we need to create a new object and pass the parent class Map object inside this pull and print the statement using second object which is created.
   3.remove (key) will remove and give the value ./if we give outside it will remove and won’t give anything if we give in print statement it will give the value in output
   remove(key , value ) will print true or false. //if we give outside it will remove(key value) and won’t give true or false it will just remove if we give in print statement it will give the value in output
   4.get(key) - if we removed already the get key value which we gonna use not it will print output as null.
   getKey() returns a keyset() method of set.

either it will print the “ value” of the key
5.Clear is used to clear() all the keys and values .
6.size() will check and give whether 3 or 4 according to ur inputs
7.Isempty() will check whether it is Empty or not.

3. Collections have only size , length is used for Strings and Arrays.

Question 2

1.What is mean by Entry?
2. Does Key value-> have duplicates?
3. why in hashmap key says as keyset()?
4.Can we say values as List in hahsmap?
5. Is map is a separate entity?
6.collection view of map and its methods?

Answer 2

1.Key + value = Entry, collection of entries is called Map
2.No Key value -> entry don’t have duplicate . Entry should be unique.
3.Because set have unique value so here key also have unique value so we call it as keyset()
4. yes we can say it , but it can also be list when it don’t have duplicate values. it is said as value list , value set.
5. yes map is a separate entity, collection of view : Map
6. Set keyset(), collectionvalues(), Set entry set().

Question 3

1. What are all the Interfaces you know?
2. What are the methods entry have?
3. What is map.entry?

Answer 3

1. Collection, List, Set comparator, comparable, navigableset, sorted set, navigablemap,
2. getkey(), get value() return type for this is Object
3. Without map there is no entry so we use Map.entry

Question 4

1. What is the use of entryset()
   2.What is the use of collectionvalues
   3..What is the use of keyset

Answer 4

1. entry set will give all the entries in [] only if we give
   Set sc = reference name(hm) .entrySet(). if we just give
   hm.entySet() and in print statment to hm it will print in curly braces
2. Same as above Collections cc = hm.values();
   it will give only values of the entries.
3. Same as above cc = hm.values();
   it will give only keys of the entries.