TreeMap program to find Iterator on keySet, values and entrySet is fail-fast in java


TreeMap - Iterator on keySet, values and  entrySet is  fail-safe or fail-fast?

The iterators returned by the iterator() method of the collections returned by all three Map's “collection view methods" are fail-fast. Means any structural modification made to TreeMap  like adding or removing elements during Iteration will throw java.util.ConcurrentModificationException.



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import java.util.TreeMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
/** Copyright (c), AnkitMittal JavaMadeSoEasy.com */
public class TreeMapFailFastExample {
public static void main(String args[]){
  
   Map<Integer,String> treeMap=new TreeMap<Integer,String>();
   treeMap.put(11, "ankit");
   treeMap.put(21, "javaMadeSoEasy");
  
   System.out.println("\n---1. Iterate on keys, by obtaining iterator on keySet---");
   //fail-fast
   Iterator<Integer> keyIterator=treeMap.keySet().iterator();
   while(keyIterator.hasNext()){
          treeMap.put(4,"newEle1");//unComment to avoid ConcurrentModificationException
          System.out.println(keyIterator.next());
   }
  
   System.out.println("\n---2. Iterate on values, by obtaining iterator on values---");
   //fail-fast
   Iterator<String> valueIterator=treeMap.values().iterator();  
   while(valueIterator.hasNext()){
          treeMap.put(4,"newEle1");//unComment to avoid ConcurrentModificationException
          System.out.println(valueIterator.next());
   }
   System.out.println("\n---3. Iterate on entry, by obtaining iterator on entrySet---");
   //fail-fast
   Iterator<Entry<Integer, String>> entryIterator=treeMap.entrySet().iterator();
   while(entryIterator.hasNext()){
          treeMap.put(4,"newEle1");//unComment to avoid ConcurrentModificationException
          System.out.println(entryIterator.next());
   }
}
}
/*OUTPUT
---1. Iterate on keys, by obtaining iterator on keySet---
Exception in thread "main" java.util.ConcurrentModificationException
   at java.util.TreeMap$PrivateEntryIterator.nextEntry(Unknown Source)
   at java.util.TreeMap$KeyIterator.next(Unknown Source)
   at TreeMapFailFastExample.main(TreeMapFailFastExample.java:24)
*/


RELATED LINKS>


HashMap - Iterate on keys by obtaining keySet, Iterate on values by obtaining values, Iterate on entry by obtaining entrySet


HashMap - synchronizing map using Collections.synchronizedMap




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