Allowing Duplicate Keys in Java Collections
Allowing Duplicate Keys in Java Collections
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Java Collections allows you to add one or more elements with the same key by using the MultiValueMap class, found in the Apache org.apache.commons.collections package (http://commons.apache.org/collections/):
package multihashmap.example;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import org.apache.commons.collections.map.MultiValueMap;
public class MultiHashMapExample {
public static void main(String[] args) {
List list;
MultiValueMap map = new MultiValueMap();
map.put("A", 4);
map.put("A", 6);
map.put("B", 7);
map.put("C", 1);
map.put("B", 9);
map.put("A", 5);
Set entrySet = map.entrySet();
Iterator it = entrySet.iterator();
System.out.println(" Object key Object value");
while (it.hasNext()) {
Map.Entry mapEntry = (Map.Entry) it.next();
list = (List) map.get(mapEntry.getKey());
for (int j = 0; j < list.size(); j++) {
System.out.println("\t" + mapEntry.getKey() + "\t " + list.get(j));
}
}
}
}Since Java Core does’t come with some solutions for supporting multiple keys, using the
org.apache.commons.collections seems to be a proper way to deal with multiple keys.
And the output is:
From http://e-blog-java.blogspot.com/2012/02/how-to-allow-duplicate-key-in-java.html
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