Array, Vector, or Hashtable?

I'm wondering what the best way to populate a names list for a chat program is. I need it to be able to set a unique identification to whoever joins the chat. It has to be able to tell who left, and be able to take just that persons name out of the list.

A Hashtable would let you match up user IDs to sockets, if that's your underlying design....

Similar Messages

Sorting a vector of hashtables

I have a vector of hashtables that I need to sort.
The hashtables contain several keys such as FirstName, LastName, ID. I need to sort this vector by the values for the LastName and FirstName keys stored in the hashtables. For example...
Vector containing the following three hashtables.
hashtable1 = {FirstName = Jill, LastName = Smyth, ID=5}
hashtable2 = {FirstName = James, LastName = Smith, ID=6}
hashtable3 = {FirstName = Jill, LastName = Smith, ID=7}
The vector needs to be sorted so the order is:
Hashtable2 (James Smith)
Hashtable3 (Jill Smith)
Hashtable1 (Jill Smyth)
Any ideas on how to do this efficiently?
Any help would be much appreciated
Thanks
--Evan

Write a comparator which can determine if one hashtable is greater than another.
Arrays.sort(myVector, myComparator);

Why is conversion from array/vector of chars to jcharArray not working?

This really is an array/vector of chars, not a string (i.e. not a char* string).
jcharArray convert(JNIEnv* env, const std:vector<char> vect)
     int size = vect.size();
     jcharArray arr = env->NewCharArray( size );
     env->SetCharArrayRegion( arr, 0, size, ( jchar * ) &( vect[ 0 ] ) );
     return arr;
}It returns garble to Java instead of the characters put into the vector. What am I doing wrong?

Presumably you have some reason to think that vect[ 0 ] is going to represent a contigous memory segement for the rest of the characters.
A java "char" and C "char" are not the same size.

ResultSet to Array/Vector

Does anyone have some code that read's data from a resultSet and puts it into a 3D array or Vector that I could look at? (3D array examples would be better).
The code I have is giving me a few problems and I was wondering how other people have implemented the above.

Try that buddy. this is similar taking it from an object and adding it to a vector and the only reason i am returning it cause i am using the vector in a jsp page...
public Vector getRecordE(String ProjectID){
               ResultSet TPRO_E=null;
               try{
               PreparedStatement P_TPRO=conOrcl.prepareStatement("select * from recorde where PROJ_EXT_PROJ_ID=?");
          //assign the ? to the argument passed
               P_TPRO.setString(1,ProjectID);
          //execute the statement
               P_TPRO.execute();
          //execute the query
               TPRO_E= P_TPRO.executeQuery();
          //looping through the resultSet
          while (TPRO_E.next()){
          //create an instance of the class
               JavaBeans ItemE = new JavaBeans();
          // set it to the Bean
               ItemE.setTwinId(TPRO_E.getString("twin_proj_id"));
               ItemE.setprojPhaseCode(TPRO_E.getString("proj_phase_cd"));
               ItemE.setEfund_cd(TPRO_E.getString("fund_cd"));
          //add the object to the vector
     V_itemsE.addElement(ItemE);
          }catch(SQLException w){
               System.out.println(w.getMessage());
          //returning the vector
                    return V_itemsE;
hope it helps... pretty close

Adding and Retriving of Vector through Hashtable

Hi,
I had a list of records from my database and I want to add it to my hashtable before passing it to another class to read. So I add my records into a vector before adding to a hashtable, but how do I read it out? Also how do I loop to store the vector in the hashtable?
(WorkOrder is another class.)
This is part of my code:
String sql_GetOrder= "SELECT * FROM WORK_ORDER WHERE ORDER_ID = '043775122N' OR ORDER_ID = '077888862L'";
rs = stmt.executeQuery(sql_GetOrder);
result = new Vector();
while (rs.next()){
wOrder = new WorkOrder();
wOrder.setOrderID(rs.getString("order_id"));
wOrder.setCompanyBRN(rs.getString("brn"));
wOrder.setSubmitBy(rs.getString("submit_by"));
wOrder.setSubmitDate(rs.getString("submit_date"));
System.out.println("Order ID: " + rs.getString("Order_id"));
result.addElement(wOrder);
myTable.put("cnt", wOrder);
wOrder = null;
System.out.println("My Vector Size: " + result.size());
WorkOrder n = (WorkOrder)myTable.get("cnt");
     if (n != null) {
         System.out.println("cnt = " + n.getOrderID());
     } Thanks

I can't do this way as you had mention:
myTable.put(wOrder.getOrderID(), wOrder);I am passing my orders to another class and the orderid is unknown to the class, so how can the other class identfiy my key?
I had done something like this:
To put in the hashtable:
String sql_GetOrder= "SELECT * FROM WORK_ORDER WHERE ORDER_ID = '043775122N'";
rs = stmt.executeQuery(sql_GetOrder);
result = new Vector();
while (rs.next()){
wOrder = new WorkOrder();
wOrder.setOrderID(rs.getString("order_id"));
System.out.println("Order ID: " + rs.getString("Order_id"));
result.addElement(wOrder);
wOrder = null;
if(result.size() > 0){
System.out.println("My result Vector Size: " + result.size());
listRecord = new Vector();
listRecord.addElement(result);
System.out.println("My listRecord Vector Size: " + listRecord.size());
myTable.put("cnt", listRecord);
}To get from hashtable:
if(!dTable.isEmpty())
Vector vList = (Vector)dTable.get("cnt");
Vector readList = new Vector();
if (vList != null) {
readList = (Vector)vList.get(0);
for (int i=0; i<readList.size(); i++){
WorkOrder w_order = new WorkOrder();
w_order = (WorkOrder)readList.get(i);
System.out.println("cnt = " + w_order.getOrderID());

Problem in converting vector to array of strings

hi
i am having a vector which in turn contains hashtable as elements
Vector v=new Vector()
Hashtable ht=new Hashtable();
v.add(ht.add("key1",value1))
v.add(ht.add("key2",value2))
v.add(ht.add("key3",value3))
v.add(ht.add("key4",value4))now i am trying to conver this vector in to a array of string like
String[] str=(String[])v.toArray(new String[v.size()]);but i am getting java.lang.ArrayStoreExceptioncan anybody help me plz
Thanks

Hi,
The api for public Object[] toArray(Object[] a) says
Returns an array containing all of the elements in this Vector in the correct order; the runtime type of the returned array is that of the specified array.
ArrayStoreException will be thrown if the runtime type of a is not a supertype of the runtime type of every element in this Vector.
The runtime type of the elements of the vector is Hashtable.
Because String is not a supertype of Hashtable the ArrayStoreException is thrown.

How to obtain Hashtable element (array) base type?

Hi,
     I have read the thread
          http://forum.java.sun.com/thread.jspa?forumID=52&threadID=531561
     on determining the base type of an object array.
     I tried applying the technique to my Hashtable where the element are arrays, this is how I am setting up my Hashtable to pass on to my native method
Hashtable ht = new Hashtable();
Float Kd[] = new Float[1];
Kd[0] = 0.1f;
Float from[] = new Float[3];
from[0] = -4.0f;
from[1] = 2.0f;
from[2] = 1.0f;
Integer indices[] = new Integer[4];
indices[0] = 217;
indices[1] = 17;
indices[2] = 769;
indices[3] = 23;
     myNativeMethod("dbname",ht);
     In my native method, I have the following which is able to determine the array size so I think it is kind of working/correct but when I tried to determine the base type of the array, I keep getting Bus error.
     Here is my native code (as part of my SWIG code)
     Should I be handling arrays obtained from Hashtable differently, can someone point out to me what the correct approach is?
Regards
8<------8<------8<------8<------8<------8<------8<------8<------
if ($input != 0) {
std::cout << "SWIG ...parameterlist..." << std::endl;
// Generated typemap code
const jclass hashtable = jenv->FindClass("java/util/Hashtable");
if (hashtable != 0) {
const jclass enumeration = jenv->FindClass("java/util/Enumeration");
const jmethodID keys =
     jenv->GetMethodID(hashtable, "keys",
               "()Ljava/util/Enumeration;");
const jmethodID get =
     jenv->GetMethodID(hashtable, "get",
               "(Ljava/lang/Object;)Ljava/lang/Object;");
if (enumeration != 0) {
     const jmethodID hasMoreElements =
     jenv->GetMethodID(enumeration,
               "hasMoreElements", "()Z");
     const jmethodID nextElement =
     jenv->GetMethodID(enumeration,
               "nextElement", "()Ljava/lang/Object;");
     for (jobject keyset = jenv->CallObjectMethod($input, keys);
     jenv->CallBooleanMethod(keyset, hasMoreElements) == JNI_TRUE;) {
     jstring key = (jstring)jenv->CallObjectMethod(keyset, nextElement);
     jarray value = (jarray)jenv->CallObjectMethod($input, get, key);
     jclass valueClass = jenv->GetObjectClass(value);
     jclass valueClassClass = jenv->GetObjectClass(valueClass);
     const jmethodID getName =
     jenv->GetMethodID(valueClass,
               "getName", "()Ljava/lang/String;");
     jstring valueClassClassName =
     (jstring)jenv->CallObjectMethod(value, getName);
     const char *vccptr = jenv->GetStringUTFChars(valueClassClassName,
                              0);
     std::cout << "vccptr is " << vccptr << std::endl;
     jenv->ReleaseStringUTFChars(valueClassClassName, vccptr);
     const char *keyptr = jenv->GetStringUTFChars(key, 0);
     std::cout << "key is " << keyptr << std::endl;
     int numElements = jenv->GetArrayLength(value);
     std::cout << "value array size is " << numElements << std::endl;
     // const char *valptr = jenv->GetStringUTFChars(value, 0);
     // $1 = CSLAddNameValue($1, keyptr, valptr);
     jenv->ReleaseStringUTFChars(key, keyptr);
     // jenv->ReleaseStringUTFChars(value, valptr);
8<------8<------8<------8<------8<------8<------8<------8<------
Regards
Message was edited by:
nicholas_yue

You've asked the same thing before. Assuming that you've defined the function prototype correctly when you built the DLL from the VI, you should be able to call it and get the results from it. You do not need to change the return type when you build the DLL. Read the information at http://zone.ni.com/devzone/conceptd.nsf/webmain/7D6A20FE02EDBF318625690700704CF3. Even though it was written for LabVIEW 6, the section on Accessing LabVIEW 6x Arrays from Microsoft Visual C++ is still valid.

Size restrictions on arrays and vectors

Hi all!!!
I want to know whether there is any restriction on maximum size of array and vectors.
If I have thousands of records to be displayed on browser through JSP, can I initialise the arrays/vectors with that no.
Whether it will have adverse effect on performance.
Thanks in anticipation

Array lists (and vectors) use an array as backing data store. And since array indices are ints, the maximum number of elements in an array list is Integer.MAX_VALUE (2 ^ 31 - 1).
About the performance: if you know how many elements you are going to add (albeit not precisely), you can create the array list with an initial capacity. This will improve performance because a new array is created when an element is to be added but the capacity has been reached.
Kind regards,
Levi

How to add vector elements to Hashtable

Hi all,
Iam having two variables like name and value.
I choosed a hashtable. I took name as key and value as value.
Now Iam willing to add another variable called order to hashtable.
I want to get both the value and order by name(key).
How can I add this order variable by Vector.
I will be very happy if write the piece of code.
Thanks a lot.
Bye

You retrieve the item from the Map in the same way you did previously.
Vector v = (Vector) myHashTable.get(key);
String value = (String) v.get(0);
String order = (String) v.get(1);
IMO it would be preferable rather than having a vector, you have a class representing the value:
public class MyObject{
String name;
String value;
String order;
}You could then put a MyObject instance into the map rather than using vectors for this.
Also note that while Vectors and Hashtables are not deprecated, there are newer (and better) equivalents in ArrayList and HashMap. You should use those in preference. For maximum flexibility declare any variables as just type List or Map - it doesn't tie you to one specific class.

Hashtables and Vectors

Hi there !!!
Today I made some stuff but still a lot more needs to be done.
So first of all let me explain what is all about.
I have to make a hashtable that contains a String as a key and a vector as a value associated with that String.The following classes extend Relation (this is an interface)
Analogy,Cause and so on.
The instances have as fields DestinationID and SourceID .
The table sorts the instances as follows : the objects with the same SourceID are put in a vector that is mapped to that SourceID.There is a second table that does the same but for the DestinationID-s
The tables I have implemented recursively
Here is the code for one of them:
public class AnnotationThread1 {
    private Vector v = new Vector();
    private Hashtable h_sourceID = new Hashtable();
    private Hashtable h_destinationID = new Hashtable();
    private Vector leaves = new Vector();
/** Creates a new instance of AnnotationThread1 */
    public AnnotationThread1() {}
/** Creates the hashtable (recursively) the key is the SourceID and the
*value is a vector that contains all the nodes that have the same SourceID
    public Hashtable add(Relation r){
        String sourceID = r.getSourceID();
        Vector v = (Vector) h_sourceID.get(sourceID);
        //if the Vector is null we create a new one
         if (v == null) v = new Vector();
        //if we add the same node twice the second will be neglected
          if (!v.contains(r)){
           v.add(r);
           h_sourceID.put(sourceID,v);
      return h_sourceID;
    }Now i should also retrieve the so called leaves : here the ID -s that are not SourceID -s . (they are not parents so to say).I have done that for every single object (i chech whether the given Relation possesses a leaf or not) but still I can not come up with an idea how to retrieve all leaves and for example to have them in a vector .
Here is the code how I check if one ID is a leaf or not:
/** Asks if a given ID is a leaf or not(uses the add() method)
*@param Relation r
*@return false if the node does not have a leaf and true otherwise
    public boolean ifLeaf(Relation r){
      boolean ifleaf = false;
      String leaf = r.getDestinationID();
      if (!h_sourceID.containsKey(leaf)){ ifleaf = true; }
      return ifleaf;
    }If anyone has ideas I will be very glad.
The same problems I have with finding the root.
Thanks in advance...

OPS I forgot to mention how is the table actually created.Well in the main class i have something like:
public static void main(String args[]){
      AnnotationThread1 example = new AnnotationThread1();
      BackgroundInformation a = new BackgroundInformation(0.1f,0.3f,"a","b");
      example.add(a);
      Analogy b = new Analogy(0.2f,0.1f,"a","c");
      example.add(b);
      SupportArgument c = new SupportArgument(0.2f,0.1f,"b","d");
      example.add(c);The Strings are as mentioned the SourceID and the DestinationID.
for example after writing
System.out.printlnexample.add(c);I will get as an output(in NetBeans):
a=[collate.AnnotationThread.BackgroundInformation@1f12c4e,    collate.AnnotationThread.Analogy@93dee9]}

Hashtable and double array

Hi,
i need to store a series of double arrays in a hashtable.
now while extracting them i get ClassCastException
can anyone tell me how to extract a double array from a hashtable. if its not possible then can i use any other data structure
thanx

Cast it correctly?double[] darray = (double[])yourHashtable.get(yourKey);And if that doesn't work, then post the code where you put the "double array" into the Hashtable.

Variable vector names???

hi,
i'm new to this java action, so sorry if this is really obvious, but i can't get this to work.
i need to assign information to a different vector within a loop so for example>>>>>>
String[] nameofvector = { "nameVector", "productVector", "typeVector" };
for (int i=1; i<= 3;i++) {
Vector eval(nameofvector) = new Vector(); //i know eval doesn't work but it's
eval(nameofvector).elementAt(i) = nameofvector[i] // there so you can see what i'm trying to do
any ideas?
thanks,
ben
btw: this is my 1st post ;)

You can use Hashtable (or one of the other Map classes). It takes a key-value pair, where the key could be the name of your vector, and the value is the vector:
Hashtable vectors = new Hashtable();
vectors.put("nameVector", new Vector());
vectors.put("productVector", new Vector());
vectors.put("typeVector", new Vector());
// to get a named vector:
Vector vector = (Vector)vectors.get("productVector");You could also have an array of vectors, and make constants for the 3 vectors.
public static final NAME_VECTOR = 0;
public static final PRODUCT_VECTOR = 0;
public static final TYPE_VECTOR = 0;
private Vector[] vectors = new Vector[3];
// ... inside the construtor:
for (int x = 0; x < vectors.length; x++) {
vectors[x] = new Vector();
// to get a vector:
Vector vector = vectors[PRODUCT_VECTOR];

Hashtable---getting value

import java.util.*;
import java.text.SimpleDateFormat;
class Test{
     public static void main(String[] args)throws Exception{
          String Holidays_val = "1/25/207|SecondHolidayDay^2/01/2007|Anotherholiday^3/01/2017|newholiday^4/02/2007|someotherholiday^5/03/2007|Firstholiday^";
          String date1="";
          String holiday1="";
          StringTokenizer str1 = new StringTokenizer(Holidays_val,"^");
          Hashtable hs = new Hashtable();
          Date dates[] =new Date[5];
          int m=0;
          while(str1.hasMoreTokens()){
               String st1 = str1.nextToken();
               StringTokenizer stk = new StringTokenizer(st1,"|");
               while(stk.hasMoreTokens()){
                    date1 = stk.nextToken();
                    holiday1 = stk.nextToken();
                    dates[m] = new Date(date1);
                    m++;
               hs.put(date1,holiday1);
          Date temp = null;
          for(int i=0;i<dates.length;i++){
               for(int j=i+1;j<dates.length;j++){
                    if(dates.after(dates[j])){
                         temp = dates[j];
                         dates[j] = dates[i];
                         dates[i] = temp;
          SimpleDateFormat dateFormat = new SimpleDateFormat("MM/dd/yyyy");
          Vector dates1 = new Vector();
          for(int k=0;k<dates.length;k++){
               dates1.addElement(dateFormat.format(dates[k]));
          Iterator iter1 = dates1.iterator();
          Vector finalVec = new Vector();
          while(iter1.hasNext()){
               String date = iter1.next().toString();
               finalVec.addElement(date);
               finalVec.addElement(hs.get(date));
               System.out.println(date);// printing the date CORRECTLY
               System.out.println(hs.get(date));//printing the corresponding holiday as NULL, when i place a hardcode date as hs.get("2/01/2007")---its printing the holiday name correctly.
               //GETTING NULL IN THE ABOVE LINE OF CODE, i should get the corresponding holiday name of the given date
               System.out.println(finalVec);
In the above code im taking the String Holidays_val, im separating the date and their corresponding holiday names, and then im sorting the dates and placing the dates and holidayname in a hashtable. finally im placing the date and its corresponding holiday in the vector, but the problem over here is im getting the null in case of corresponding holiday while putting in Hashtable.

Is this a joke?
Why are you turning the strings into dates, and then back into strings again?.
Even if the strings at both ends of the process are identical, it's a strange thing to do.
You should key the hashtable off of the Date objects.
Other issues:
You're using a deprecated constructor for Date. Use java.text.SimpleDateFormat to parse the date string and get a Date object.
Drop that whole thing when you turn dates back into strings.
Why do you add things to arrays, and then put them into vectors? Just add the Date objects directly into a vector.
But better yet, don't use Vector. Use a more modern List implementation, like ArrayList. And use a HashMap rather than a Hashtable.
And write to interfaces; the types of variables should be List and Map, not Vector or Hashtable (or ArrayList or HashMap).
Don't do the sort yourself. Use java.util.Collections.sort.
And you don't really need a separate List and a Map. Just use a SortedMap.
You can do this whole thing in less than half the code, and it'll work better too.

JTable + Hashtable + Collection doesn't seem to work properly

Hi folks,
I'm having a problem with JTree class. Basically, I want to instantiate it by using an Hashtable, though
depending on the fact that I use collection or arrays the result can substantially vary.
Take the following use case:
import javax.swing.*;
import java.util.*;
public class Tree extends JApplet{
public Tree(){
    super();
    setSize(300, 250);
    init();
    setVisible(true);
public void init(){
    Hashtable<String,List<String>> hash = new Hashtable<String,List<String>>();
    hash.put("Foo", Arrays.asList("Bar"));
    JTree tree = new JTree(hash);
    getContentPane().add(tree);
}This displays a wrong tree, in fact you should have a Foo node that contains a Bar leaf.
Now if I use array instead of collections (generics are not the problem) everything work just as
expected!?
import javax.swing.*;
import java.util.*;
public class Tree extends JApplet{
public Tree(){
    super();
    setSize(300, 250);
    init();
    setVisible(true);
public void init(){
    Hashtable<String,String [] > hash = new Hashtable<String,String []>();
    hash.put("Foo", new String []{"Bar"});
    JTree tree = new JTree(hash);
    getContentPane().add(tree);
}Considering that the constructor of JTree allows the following instantiation for Hastable:
public JTree(Hashtable<?,?> value)the use of wildcards let me assume that I can put whatever I like as the type of my keys/values.
Am I missing something or this is indeed some very strange (buggy) behavior.
Cheers,
Mirco

lins314159 wrote:
[Javadocs for createChildren method|http://java.sun.com/javase/6/docs/api/javax/swing/JTree.DynamicUtilTreeNode.html#createChildren%28javax.swing.tree.DefaultMutableTreeNode,%20java.lang.Object%29]
If you look in the source code for JTree, there's no mention of Lists in there. Not quite sure why they handle Vectors and Hashtables only instead of Lists and Maps.Hi lins,
thanks for taking the time for giving me your though.
I have take a glance at the javadoc for method createChildren, but once again it tells me that if I have an entry of the type
<A,Collection<B>> I should get a Node named after the object of type A and whose leaf are the ones contained in the collection.
I agree with you that is bizarre that the JTree constructor only accept Hashtable (and not Map, that appear to me more convenient);
but I can live with that as long as the value field of the hashtable behave as I would expect.
I'm not an experienced Java programmer, so if any of you gurus has any thoughts on that, please let me know.
Cheers,
Mirco
Edited by: Mirco on Feb 29, 2008 12:07 AM

How to create a vector object

hi,
ok my problem is i am trying to create a vector object in jbuilder with this
private Vector<Object> rows;
but i keep getting a error saying generics are not supported in 1.2 try -source 1.5.
how can i create a vector object in 1.2, i am seriously stuck can you please help.
regards

i now got the 1.5 to work without the invocation errors, the whole reason i needed the array is as such
setting array
Vector<Object> rows;
then
public void setauctiondetails() throws java.rmi.RemoteException {
Connection link = null;
Statement statement = null;
ResultSet results = null;
Class.forName(
"sun.jdbc.odbc.JdbcOdbcDriver");
link = DriverManager.getConnection(
"jdbc:odbc:auction","","");
statement = link.createStatement();
results = statement.executeQuery(
"SELECT * FROM auctiondetails");
rows = new Vector<Object>();
while (results.next())
rows.addElement(results.getInt(1));
rows.addElement(results.getString(2));
rows.addElement(results.getString(3));
rows.addElement((results.getInt(4)));
link.close();
for(int i=0; i<clients.size(); i++){
icl = (Iclient)clients.get(i);
icl.updateTime(rows);
but still getting a error with the bloody array saying "type java.util.vector does not take parameters". i no you guys are really good at java, so tried not to have a go just need to be pointed to a tutorial or some code that might explain this better to me.
kind regards

Array, Vector, or Hashtable?

Similar Messages

Maybe you are looking for