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Java Generics

Posted on 2007-03-20
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Last Modified: 2012-05-05
Hi guys. I have a program which I've successfully implemented that uses Hash maps. The problem is that I have done it the 'old way' and am struggling to update it to Generics.

Rather than try to get you to update my code, I wondered if you could take the example below and show me how that would be implemented in Generics. I know the changes needed are minor.

Thanks.

This example is found at http://www.exampledepot.com/egs/java.util/coll_HashTables.html?l=rel
// Create a hash table
    Map map = new HashMap();    // hash table
    map = new TreeMap();        // sorted map
   
    // Add key/value pairs to the map
    map.put("a", new Integer(1));
    map.put("b", new Integer(2));
    map.put("c", new Integer(3));
   
    // Get number of entries in map
    int size = map.size();        // 2
   
    // Adding an entry whose key exists in the map causes
    // the new value to replace the old value
    Object oldValue = map.put("a", new Integer(9));  // 1
   
    // Remove an entry from the map and return the value of the removed entry
    oldValue = map.remove("c");  // 3
   
    // Iterate over the keys in the map
    Iterator it = map.keySet().iterator();
    while (it.hasNext()) {
        // Get key
        Object key = it.next();
    }
   
    // Iterate over the values in the map
    it = map.values().iterator();
    while (it.hasNext()) {
        // Get value
        Object value = it.next();
    }
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Question by:pendulumx
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6 Comments
 
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by:
TimYates earned 100 total points
ID: 18756888
   Map<String,Integer> map = new HashMap<String,Integer>();    // hash table
    map = new TreeMap<String,Integer>();        // sorted map
   
    // Add key/value pairs to the map
    map.put("a", new Integer(1));
    map.put("b", new Integer(2));
    map.put("c", new Integer(3));
   
    // Get number of entries in map
    int size = map.size();        // 2
   
    // Adding an entry whose key exists in the map causes
    // the new value to replace the old value
    Integer oldValue = map.put("a", new Integer(9));  // 1
   
    // Remove an entry from the map and return the value of the removed entry
    oldValue = map.remove("c");  // 3
   
    // Iterate over the keys in the map
    for( String key : map.keySet() )
    {
    }
   
    // Iterate over the values in the map
    for( Integer value : map.values() )
    {
    }

Should do it...
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LVL 30

Expert Comment

by:Mayank S
ID: 18756956
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Assisted Solution

by:Mayank S
Mayank S earned 25 total points
ID: 18756981
You can also make use of autoboxing:

>> map.put("a", new Integer(1));

map.put ( "a", 1 ) ;
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LVL 35

Expert Comment

by:TimYates
ID: 18757041
*shudder*

;-)
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Author Comment

by:pendulumx
ID: 18757208
Excellent - thank you :)
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Expert Comment

by:Mayank S
ID: 18757419
:-)
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