81. Which of these standard collection classes implements a linked list data structure?

1. 1. AbstractSet

   
   
   

   2. HashSet

   
   
   

   3. AbstractList

   
   
   

   4. LinkedList

   
   
   

   5. None of these

   
   
   

---

1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   LinkedList

---

82. If large number of items are stored in hash bucket, what happens to the internal structure?

1. 1. Any further addition throws Overflow exception

   
   
   

   2. The LinkedList will be replaced by another hashmap

   
   
   

   3. The bucket will increase its size by a factor of load size defined

   
   
   

   4. The bucket will switch from LinkedList to BalancedTree

   
   
   

   5. None of these

   
   
   

---

1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   BalancedTree will improve performance from O(n) to O(log n) by reducing hash collisions.

---

---

83. What is the output of below snippet?
    

    import java.util.*;
    public class Map_Example
    {
      public static void main(String[] args)
      {
    		Map mapSample = new TreeMap();
    		mapSample.put(4, null); 
    		mapSample.put(0, null); 
    		mapSample.put(3, null); 
    		mapSample.put(2, null); 
    		mapSample.put(1, null); 
     
           System.out.println(mapSample);
       }
    }
    

1. 1. {0=null, 1=null, 2=null, 3=null, 4=null}

   
   
   

   2. Runtime Error

   
   
   

   3. Compilation Error

   
   
   

   4. {3=null, 0=null, 2=null, 1=null, 4=null}

   
   
   

   5. None of these

   
   
   

---

1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   HashMap needs unique keys. TreeMap sorts the keys while storing objects.

---

84. How to externally synchronize hashmap?

1. 1. Collections.synchronize(new HashMap());

   
   
   

   2. Collections.synchronizedMap(new HashMap());

   
   
   

   3. HashMap.synchronize(HashMap a);

   
   
   

   4. HashMap a = new HashMap();
      a.synchronize();

   
   
   

   5. None of these

   
   
   

---

1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   Collections.synchronizedMap() synchronizes entire map. ConcurrentHashMap provides thread safety without synchronizing entire map.

---

---

85. If two threads access the same hashmap at the same time, what would happen?

1. 1. RuntimeException

   
   
   

   2. ClassNotFoundException

   
   
   

   3. NullPointerException

   
   
   

   4. ConcurrentModificationException

   
   
   

   5. None of these

   
   
   

---

1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   The code will throw ConcurrentModificationException if two threads access the same hashmap at the same time.

---