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How do i use an iterator to get data from a hashtable?

Posted on 2002-04-03
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Last Modified: 2010-05-18
I am having a bit of trouble understanding collections in Java and how they relate to iterators.

I have a hashtable  - ResTable(res, value); and i need to use an iterator to go through each element in my hash table and copy the value res into a string array and also copy value into a separate int array.  How do i go about defining the iterator for my hashtable?
 
 
private static void CopyToArray(){
       
// I know that i have to define my collection by something like...  
   Collection myCollection = .....;  //  do i assign ResTable equal to mycollection?    How??
//Then i can say...
   Iterator i = myCollection.iterator();
   while (i.hasNext()){
      System.out.println(i.next());
      // Do what i need to to convert data from hash table to array
      //Cast datatype etc
   }
}
 

Any seggestion in either code format, psuedocode or basic english would be much appreciated.

Nutty
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Question by:Nuttman
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5 Comments
 
LVL 3

Expert Comment

by:rjackman
ID: 6917143
it seems that u want to get the values without knowing the keys in the table then u can do the following
Set keys = ResTable.keySet();
for(Iterator itr = keys.iterator();itr.hasNext();)
{
   String key = (String)itr.next();
   System.our.println("Keys---->"+key);
   System.out.println("Value--->"+ResTable.get(key));
}

cheers
RJ
0
 
LVL 6

Expert Comment

by:kotan
ID: 6917259
You don't need to assign ResTable to Collection. Because it is already a Collection.

To extract the keys of ResTable into String array,
String[] strArr = (String[]) ResTable.keySet().toArray(new String[0]);

For values, You can only copy into Integer object but not int primitive type.

Integer[] iArr = (Integer[]) ResTable.values().toArray(new Integer[0]);
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LVL 1

Accepted Solution

by:
jose_tijo earned 25 total points
ID: 6917692
/*
 * HashToArray.java
 *
 * Created on 04 April 2002, 10:47
 */

/**
 *
 * @author  Tijo Jose
 * @version 1.0
 */
public class HashToArray {

    java.util.Hashtable hashTable;
   
    String[] stringArray;
   
    int[] intArray;
   
    Object[] objArray;
   
    java.util.Enumeration enumeration;
   
    public int Count;
   
    /** Creates new HashToArray */
    public HashToArray() {
        hashTable = new java.util.Hashtable();
        hashTable.put("One", "1" );
        hashTable.put("Two", "2");
        hashTable.put("Three", "3");
        stringArray = new String[hashTable.size()];
        intArray = new int[hashTable.size()];
    }

    /**
    * @param args the command line arguments
    */
    public static void main (String args[]) {
        HashToArray hta = new HashToArray();
        hta.CopyToArray();
    }

    public void CopyToArray() {
        objArray = hashTable.values().toArray();
        Count = 0;
        while(objArray.length > Count) {
            intArray[Count] = (new Integer(objArray[Count].toString())).intValue();
            Count ++;
        }
        Count = 0;
        while(intArray.length > Count) {
            System.out.println("Int - > " + intArray[Count]);
            Count++;
        }
       
        Count = 0;
        stringArray = (String[])hashTable.keySet().toArray(new String[0]);
        if(this.stringArray != null) {
            while(stringArray.length > Count) {
                System.out.println("String - > " + stringArray[Count]);
                Count++;
            }
        }
    }
}
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LVL 5

Expert Comment

by:vemul
ID: 7898939
No comment has been added lately, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area that this question is:

- points to jose_tijo

Please leave any comments here within the
next seven days.

PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER !

vemul
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Expert Comment

by:Computer101
ID: 7959864
Comment from expert accepted as answer

Computer101
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