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Core Java - Interview Questions and Answers for 'Treemap' - 17 question(s) found - Order By Newest

Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q1. Difference between TreeMap and HashMap ?Core Java
Ans. They are different the way their elements are stored in memory. TreeMap stores the Keys in order whereas HashMap stores the key value pairs randomly.

  Sample Code for treemap

  Sample Code for hashmap

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 Q2. What is comparator interface used for ?Core Java
Ans. The purpose of comparator interface is to compare objects of the same class to identify the sorting order. Sorted Collection Classes ( TreeSet, TreeMap ) have been designed such to look for this method to identify the sorting order, that is why class need to implement Comparator interface to qualify its objects to be part of Sorted Collections.

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 Q3. Which of the following collection maintain its elements in Natural Sorted order ?

a. HashMap
b. TreeMap
c. LinkedHashMap
d. LinkedMap
Ans. TreeMap

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 Q4. Which are the sorted collections ?Core Java
Ans. TreeSet and TreeMap

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 Q5. How can we reverse the order in the TreeMap ?
Ans. Using Collections.reverseOrder()

Map tree = new TreeMap(Collections.reverseOrder());

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 Q6. TreeMap orders the elements on which field ?
Ans. Keys

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 Q7. How TreeMap orders the elements if the Key is a String ?
Ans. As String implements Comparable, It refers to the String compareTo method to identify the order relationship among those elements.

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 Q8. Can we add heterogeneous elements into TreeMap ?
Ans. No, Sorted collections don't allow addition of heterogeneous elements as they are not comparable.

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 Q9. Will it create any problem if We add elements with key as user defined object into the TreeMap ?
Ans. It won't create any problem if the objects are comparable i.e we have that class implementing Comparable interface.

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  Q10. Can we have null keys in TreeMap ?Core Java
Ans. No, results in exception.

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 Q11. Can value be null in TreeMap ?Core Java
Ans. Yes.

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 Q12. Which interface TreeMap implements ?
Ans. TreeMap implements NavigableMap, SortedMap, Serializable and Clonable.

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 Q13. Which tree is used to implement TreeMap in Java?
Ans. Red Black Tree

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 Q14. If we add Enum constants to a sorted collection ( Treemap , TreeSet ), What will be the order in which they will be maintained ?

a. Sorted Collection wont maintain them in any order.
b. Insertion Order
c. Order in which constants are declared.
d. Natural Sorting Order.
Ans. Order in which constants are declared.

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 Q15. What is the difference between TreeSet and TreeMap ?Core Java
Ans. TreeSet contains only values as elements whereas TreeMap contains Key value pairs.

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 Q16. How to sort objects based on one of the field ?Core Java
Ans. Using comparable and comparator and sorted collections like TreeSet or TreeMap.

or

use stream api from java 8 onwards which internally refers to comparable and comparator through lambda expressions

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 Q17. Difference between TreeMap and SortedMap ?Core Java
Ans. sortedMap is an interface ,while TreeMap is an implementation of sortMap.

We can not create an instance of sortedMap but we can create an instance of treeMap

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