Differences and Similarities between TreeMap and ConcurrentSkipListMap with program in java
It’s very important to differentiate between java.util.TreeMap and java.util.concurrent.ConcurrentSkipListMap, so in this Collection framework tutorial we will learn what are differences and similarities between java.util.TreeMap and java.util.concurrent.ConcurrentSkipListMap in java.
Contents of page :
  • Differences between java.util.TreeMap and java.util.concurrent.ConcurrentSkipListMap in java >
  • Similarity between java.util.TreeMap and java.util.concurrent.ConcurrentSkipListMap in java >
  • Program 1 to show
    • The iterators returned by the iterator() method of TreeMap are fail-fast in java>
  • Program 2 to show
    • The iterators returned by the iterator() method of ConcurrentSkipListMap are fail-safe in java >


Differences between java.util.TreeMap and java.util.concurrent.ConcurrentSkipListMap in java >

Property
java.util.TreeMap
java.util.concurrent. ConcurrentSkipListMap
1
synchronization
TreeMap is not synchronized  (because 2 threads on same TreeMap object can access it at same time) in java.

ConcurrentSkipListMap is synchronized (because 2 threads on same ConcurrentSkipListMap object cannot access it at same time) in java.
2
Iterator
The iterators returned by the iterator() method of Map's “collection view methods" are fail-fast>
  • map.keySet().iterator()
  • map.values().iterator()
  • map.entrySet().iterator()

all three iterators are fail-fast, means any structural modification made to TreeMap during iteration using any of 3 Iterator will throw ConcurrentModificationException.

As shown in Program 1 below.
The iterators returned by the iterator() method of Map's “collection view methods" are fail-safe >
  • map.keySet().iterator()
  • map.values().iterator()
  • map.entrySet().iterator()

all three iterators are fail-safe.





As shown in Program 2 below.
3
Performance
TreeMap is not synchronized, hence its operations are faster as compared to ConcurrentSkipListMap.
ConcurrentSkipListMap is synchronized, hence its operations are slower as compared to TreeMap.
4
Introduced inin which java version
TreeMap was introduced in second version of java i.e. JDK 2.0
ConcurrentSkipListMap was introduced in sixth version of java i.e. JDK 6.0
5
Package
java.util
java.util.concurrent
6
Implements which interface
Map
SortedMap
NavigableMap
Map
SortedMap
NavigableMap
ConcurrentNavigableMap


So far we have learned what are differences between java.util.TreeMap and java.util.concurrent.ConcurrentSkipListMap in java.
Now we will learn similarities in java.util.TreeMap and java.util.concurrent.ConcurrentSkipListMap in Collection framework in java.
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Similarity between TreeMap and ConcurrentSkipListMap in java>

Property
java.util.TreeMap and java.util.concurrent.ConcurrentSkipListMap
1
Insertion order
TreeMap and ConcurrentSkipListMap both are sorted by natural order of keys in java.
2

TreeMap and ConcurrentSkipListMap both does not allow to store null key but allow many null values in java.
Any attempt to store null key throws runtimeException (NullPointerException).
3
Implements java.util.Map
TreeMap and ConcurrentSkipListMap both are implementation of the java.util.Map interface in java.
4
Complexity
Complexity offered by methods of TreeMap and ConcurrentSkipListMap both of these is same in java.

Operation/ method
Best case
put(K key, V value)
O(log(n))
get(Object key)
O(log(n))
remove
O(log(n))


Example/Program 1 to show
The iterators returned by the iterator() method of TreeMap are fail-fast >
  • map.keySet().iterator()
  • map.values().iterator()
  • map.entrySet().iterator()
all three iterators are fail-fast, means any structural modification made to TreeMap during iteration using any of 3 Iterator will throw ConcurrentModificationException.
Also, iteration done on TreeMap using enhanced for loop is Fail-fast in java.
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeMap;
public class TreeMapExample {
   public static void main(String args[]) {
          Map<Integer, String> treeMap = new TreeMap<Integer, String>();
          treeMap.put(11, "audi");
          treeMap.put(21, "bmw");
          treeMap.put(31, "ferrari");
          //fail-fast
          Iterator<Integer> keyIterator = treeMap.keySet().iterator();
          while (keyIterator.hasNext()) {
                 treeMap.put(4, "porsche");//unComment to avoid ConcurrentModificationException
                 System.out.println(keyIterator.next());
          }
          //enhanced for loop on keys is fail-fast
          Set<Integer> keySet = treeMap.keySet();
          for (Integer key : keySet) {
                 treeMap.put(4, "porsche");//unComment to avoid ConcurrentModificationException
                 System.out.println(key);
          }
         
          //fail-fast
          Iterator<String> valueIterator = treeMap.values().iterator();
          while (valueIterator.hasNext()) {
                 treeMap.put(4, "porsche");//unComment to avoid ConcurrentModificationException
                 System.out.println(valueIterator.next());
          }
          //enhanced for loop on values is fail-fast
          Collection<String> collection = treeMap.values();
          for (String value : collection) {
                 treeMap.put(4, "porsche");//unComment to avoid ConcurrentModificationException
                 System.out.println(value);
          }
          //fail-fast
          Iterator<Entry<Integer, String>> entryIterator = treeMap.entrySet()
                       .iterator();
          while (entryIterator.hasNext()) {
                 treeMap.put(4, "porsche");//unComment to avoid ConcurrentModificationException
                 System.out.println(entryIterator.next());
          }
          //enhanced for loop on entry is fail-fast
          Set<Entry<Integer, String>> entrySet = treeMap.entrySet();
          for (Entry<Integer, String> entry : entrySet) {
                 treeMap.put(4, "porsche");//unComment to avoid ConcurrentModificationException
                 System.out.println(entry);
          }
   }
}
In above program structural modification was made to TreeMap during iteration, and that didn’t throwed ConcurrentModificationException.


Example/Program 2 to show
The iterators returned by the iterator() method of ConcurrentSkipListMap are fail-safe >
  • map.keySet().iterator()
  • map.values().iterator()
  • map.entrySet().iterator()
all three iterators are fail-safe.
Also, iteration done on ConcurrentSkipListSet using enhanced for loop is Fail-safe in java.
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.concurrent.ConcurrentSkipListMap;
public class ConcurrentSkipListMapExample {
   public static void main(String args[]) {
          Map<Integer, String> concurrentSkipListMap = new ConcurrentSkipListMap<Integer, String>();
          concurrentSkipListMap.put(11, "audi");
          concurrentSkipListMap.put(21, "bmw");
          concurrentSkipListMap.put(31, "ferrari");
         
          // fail-safe
          Iterator<Integer> keyIterator = concurrentSkipListMap.keySet()
                       .iterator();
          while (keyIterator.hasNext()) {
                 System.out.println(keyIterator.next());
          }
          // enhanced for loop on keys is fail-safe
          Set<Integer> keySet = concurrentSkipListMap.keySet();
          for (Integer key : keySet) {
                 concurrentSkipListMap.put(4, "porsche");
                 System.out.println(key);
          }
          // fail-safe
          Iterator<String> valueIterator = concurrentSkipListMap.values()
                       .iterator();
          while (valueIterator.hasNext()) {
                 concurrentSkipListMap.put(5, "porsche");
                 System.out.println(valueIterator.next());
          }
          // enhanced for loop on values is fail-safe
          Collection<String> collection = concurrentSkipListMap.values();
          for (String value : collection) {
                 concurrentSkipListMap.put(6, "porsche");
                 System.out.println(value);
          }
          // fail-safe
          Iterator<Entry<Integer, String>> entryIterator = concurrentSkipListMap
                       .entrySet().iterator();
          while (entryIterator.hasNext()) {
                 concurrentSkipListMap.put(7, "porsche");
                 System.out.println(entryIterator.next());
          }
          // enhanced for loop on entry is fail-safe
          Set<Entry<Integer, String>> entrySet = concurrentSkipListMap.entrySet();
          for (Entry<Integer, String> entry : entrySet) {
                 concurrentSkipListMap.put(8, "porsche");
                 System.out.println(entry);
          }
   }
}
In above program structural modification was made to ConcurrentSkipListMap during iteration, but that didn’t throw ConcurrentModificationException in java.


So in this Collection framework tutorial we learned what are differences and similarities between java.util.TreeMap and java.util.concurrent.ConcurrentSkipListMap in java.



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