Question-181. What is the difference between Iterator and Enumeration ?
Answer-
| Iterator | Enumeration |
|---|---|
| 1) Iterator can traverse legacy and non-legacy elements. | 1) Enumeration can traverse only legacy elements. |
| 2) Iterator is fail-fast. | 2) Enumeration is not fail-fast. |
| 3) Iterator is slower than Enumeration. | 3) Enumeration is faster than Iterator. |
Question-182. What is the difference between List and Set ?
Answer- List can contain duplicate elements whereas Set contains only unique elements.
Question-183. What is the difference between HashSet and TreeSet ?
Answer- HashSet maintains no order whereas TreeSet maintains ascending order.
Question-184. What is the difference between Set and Map ?
Answer- Set contains values only whereas Map contains key and values both.
Question-185. What is the difference between HashSet and HashMap ?
Answer- HashSet contains only values whereas HashMap contains entry(key,value). HashSet can be iterated but HashMap need to convert into Set to be iterated.
Question-186. What is the difference between HashMap and TreeMap ?
Answer- HashMap maintains no order but TreeMap maintains ascending order.
Question-187. What is the difference between HashMap and Hashtable ?
Answer-
| HashMap | Hashtable |
|---|---|
| 1) HashMap is not synchronized. | 1) Hashtable is synchronized. |
| 2) HashMap can contain one null key and multiple null values. | 2) Hashtable cannot contain any null key or null value. |
Question-189. What is the difference between Collection and Collections ?
Answer- Collection is an interface whereas Collections is a class. Collection interface provides normal functionality of data structure to List, Set and Queue. But, Collections class is to sort and synchronize collection elements.
Question-190. What is the difference between Comparable and Comparator ?
Answer-
| Comparable | Comparator |
|---|---|
| 1) Comparable provides only one sort of sequence. | 1) Comparator provides multiple sort of sequences. |
| 2) It provides one method named compareTo(). | 2) It provides one method named compare(). |
| 3) It is found in java.lang package. | 3) it is found in java.util package. |
| 4) If we implement Comparable interface, actual class is modified. | 4) Actual class is not modified |