public V putIfAbsent(K key, V value)
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What do putIfAbsent method do>
If map does not contain specified key, put specified key-value pair in map and return null.
If map already contains specified key, return value corresponding to specified key.
putIfAbsent method is equivalent to writing following code >
synchronized (map){
if (!map.containsKey(key))
return map.put(key, value);
else
return map.get(key);
}
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Full Program to use putIfAbsent method >
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
/** Copyright (c), AnkitMittal JavaMadeSoEasy.com */
public class ConcurrentHashMapTest {
public static void main(String args[]) {
ConcurrentMap<Integer, String> concurrentHashMap =
new ConcurrentHashMap<Integer, String>();
concurrentHashMap.put(1, "javaMadeSoEasy");
System.out.println("concurrentHashMap : "+concurrentHashMap);
System.out.println("\n putIfAbsent method >> "+
concurrentHashMap.putIfAbsent(1, "ankit"));
System.out.println("concurrentHashMap : "+concurrentHashMap);
System.out.println("\n putIfAbsent method >> "+
concurrentHashMap.putIfAbsent(2, "audi"));
System.out.println("concurrentHashMap : "+concurrentHashMap);
}
}
/*OUTPUT
concurrentHashMap : {1=javaMadeSoEasy}
putIfAbsent method >> javaMadeSoEasy
concurrentHashMap : {1=javaMadeSoEasy}
putIfAbsent method >> null
concurrentHashMap : {2=audi, 1=javaMadeSoEasy}
*/
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concurrentHashMap.putIfAbsent(1, "ankit") > returned javaMadeSoEasy because map was already having that key.
concurrentHashMap.putIfAbsent(2, "audi") > putted specified key-value pair in map and returned null because map wasn’t having that key.
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Labels:
Collection programs
Core Java