The difference between Hashtable and HashMap

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Summarize

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One important difference between these two things is that Hashtable is thread-safe, and HashMap is thread insecure.

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HashMap to achieve synchronization through an additional synchronization mechanism: a static method of the general collections is resolved: Map m = collections.synchronizedmap (new HashMap (...));

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This method returns a synchronized map that encapsulates all the methods of the underlying hashmap, making the underlying hashmap secure even in multi-threaded environments.

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In addition Hashtable key and value are not null, and HashMap can,HashMap can be used Null is a key (of course there can be only one), and a null value is allowed, which can be used by one or more keys to correspond to a null value.

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Another important difference is that Hashtable inherits from the dictionary class and HashMap inherits from the map interface.

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Test

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For example, I also add 2,000,000 the same string to the two data structures to compare the time of its insertion

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117 Millis have passed when using HashTable.

Millis have passed when using HASHMAP.

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Test code

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public class Hashmapandhashtable {

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private static final String base = "base string.";

private static final int count = 2000000;

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public static void Hashmaptest () {

String key= "Hello";

String value= "World";

Long begin, end;

Begin = System.currenttimemillis ();

Hashmap<string, string> hashmap=new hashmap<> ();

for (int i = 0; i < count; i++) {

Hashmap.put (key, value);

}

End = System.currenttimemillis ();

System.out.println ((End-begin)

+ "Millis have passed when using HashMap.");

}

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public static void Hashtabletest () {

String key= "Hello";

String value= "World";

Long begin, end;

Begin = System.currenttimemillis ();

Hashtable<string, String>hashtable=new hashtable<> ();

for (int i = 0; i < count; i++) {

Hashtable.put (key, value);

}

End = System.currenttimemillis ();

System.out.println ((End-begin)

+ "Millis have passed when using HashTable.");

}

public static void Main (string[] args) {

TODO auto-generated Method Stub

Hashtabletest ();

Hashmaptest ();

}

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}

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The difference between Hashtable and HashMap