Shulou(Shulou.com)06/02 Report--

This article is to share with you about the four ways of traversing ConcurrentHashMap in Java. The editor thinks it is very practical, so I share it with you. I hope you can get something after reading this article. Let's take a look at it.

Method 1: use entries in the for-each loop to traverse

System.out.println ("method 1: use entries to traverse in a for-each loop")

For (Map.Entry entry: map.entrySet ()) {

System.out.println ("Key =" + entry.getKey () + ", Value =" + entry.getValue ())

}

Method 2: traverse keys or values in the for-each loop, which is suitable for situations where values or keys are needed. Method 2 is 10% faster than method 1.

System.out.println ("method 2: traversing keys or values in a for-each loop, which is suitable for situations where a value or key is required"); / / traversing key for (String key: map.keySet ()) {System.out.println ("key =" + key);} / / traversing value for (String value: map.values ()) {System.out.println ("value =" + value);}

Method 3: use Iterator traversal, use concurrent collections to report no exceptions, and the performance is similar to method 2.

/ / use generic Iterator entries = map.entrySet () .iterator (); System.out.println ("use Iterator traversal and use generics:")

While (entries.hasNext ()) {Map.Entry entry = entries.next ()

System.out.println ("Key =" + entry.getKey () + ", Value =" + entry.getValue ()); / / Note that the collection is manipulated here, and the traversal below will not print 0 again.

If ("0" .equals (entry.getKey () {map.remove (entry.getKey ())

}

}

/ / do not use generics

Iterator entrys = map.entrySet () .iterator ()

System.out.println ("use Iterator traversal and do not use generics")

While (entrys.hasNext) {Map.Entry entry = (Map.Entry) entrys.next ()

String key = (String) entry.getKey ()

String value = (String) entry.getValue ()

System.out.println ("Key =" + key + ", Value =" + value)

}

Method 4: traversing by finding values through keys, this method is quite inefficient and is not recommended.

System.out.println ("Mode 4: traversing values through keys")

For (String key: map.keySet ()) {String value = map.get (key)

System.out.println ("Key =" + key + ", Value =" + value)

}

}

These are the four ways to traverse ConcurrentHashMap in Java. The editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

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