ConcurrentHashMap - 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-safe. Means any structural modification made to ConcurrentHashMap like adding or removing elements during Iteration won’t throw any Exception.
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import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.concurrent.ConcurrentHashMap;
/** Copyright (c), AnkitMittal JavaMadeSoEasy.com */
public class ConcurrentHashMapFailFastExample {
public static void main(String args[]){
Map<Integer,String> concurrentHashMap=new ConcurrentHashMap<Integer,String>();
concurrentHashMap.put(11, "ankit");
concurrentHashMap.put(21, "javaMadeSoEasy");
System.out.println("\n---1. Iterate on keys, by obtaining iterator on keySet---");
//fail-fast
Iterator<Integer> keyIterator=concurrentHashMap.keySet().iterator();
while(keyIterator.hasNext()){
concurrentHashMap.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=concurrentHashMap.values().iterator();
while(valueIterator.hasNext()){
concurrentHashMap.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=concurrentHashMap.entrySet().iterator();
while(entryIterator.hasNext()){
concurrentHashMap.put(4,"newEle1");//unComment to avoid ConcurrentModificationException
System.out.println(entryIterator.next());
}
}
}
/*OUTPUT
---1. Iterate on keys, by obtaining iterator on keySet---
21
11
---2. Iterate on values, by obtaining iterator on values---
newEle1
javaMadeSoEasy
ankit
---3. Iterate on entry, by obtaining iterator on entrySet---
4=newEle1
21=javaMadeSoEasy
11=ankit
*/
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RELATED LINKS>
HashMap - Iterate on keys by obtaining keySet, Iterate on values by obtaining values, Iterate on entry by obtaining entrySet
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ArrayList - add, add element at specific index methods program
Labels:
Core Java