Associative Arrays

[mayhewj7]

Does anyone have any examples of an associative array? I have one that I am working on but im getting nowhere fast with it. Could anyone tell me how to go about doing this? thanks.




import java.util.*;

public class AssociativeArray {

/**
* Private instance of the array count
*/
private int count;

/**
* Private instance of the default size of the associative array
*/
private int DEFAULT;

/**
*Private instance of the integer of an empty array.
*/
final int NOT_FOUND = -1;

/**
* Private instance array of cells
* i.e. key is the string that acts as an index, data is the data (duh)
*/
private Cell[] collect;


/
public AssociativeArray(){
count = 0;
collect = (Cell[])(new Cell[DEFAULT]);
}

private class Cell{


Object key;
Object data;

private Cell(Object key, Object data) {

}

public Object getKey(){
return key;
}

public void setKey(Object _key){
key = _key;
}

public Object getData(){
return data;
}

public void setData(Object _data){
data = _data;
}

}



public void clear(){

}

public Object get(Object key){
boolean found = false;

for(int i = 0; i < count; i++){
if(collect[i].getKey().equals(key)){
found = true;
return collect[i].getData();
}
}
if(found == false){
System.out.println("You entered an invalid key");
}

return key;

}


private void expandCapacity(){
Cell[] larger = (new Cell[collect.length*2]);

for(int index=0; index < collect.length; index++){
larger[index] = collect[index];
}
collect = larger;

}



boolean contains(Object key){

int search = 0;

for(int i = 0; i < count; i++){
if(key.equals(collect[i].getKey())){
search = i;
}
}

return (search != NOT_FOUND);
}

boolean isEmpty(){
return (count == 0);
}

public void put(Object _key, Object _data){
for(int i = 0; i < count; i++){
if(size() == collect.length){
expandCapacity();
}
if(!(contains(_key))){
collect[count] = new Cell(_key, _data);
count++;
}

else if(contains(_key)){
for(int j = 0; j < count; j++){
collect[j].setData(_data);
collect[count] = new Cell(_key, _data);
count++;
}
}
}

}

void remove(Object _key){

int search = NOT_FOUND;
//If it's empty, we're going to throw a NullPointerException
if(isEmpty()){
throw new NullPointerException();
}
//Searching for the key
for(int index=0; index < count && search == NOT_FOUND; index++){
if(collect[index].getKey() == _key){
search = index;
}

}
//It's not found, screw it!
if(search == NOT_FOUND){
System.out.println("There is no such key. Try again.");
}

//Otherwise, delete it!
else{

collect[search] = collect[count-1];
collect[count-1] = null;
count--;
}




}
//Correct
int size(){
return count;
}

//Later
public String toString(){
String info = "";
for(int i = 0; i < count; i++){
info = info + collect[i] + "\n";
}
return info;
}



The testing main method


public class Tester {

public static void main(String args[]){
AssociativeArray a = new AssociativeArray();
a.put("Jim","Rome");
a.put("Fred","Smith");
System.out.println(a);
//{[Julian,Dymacek], [Fred,Smith]}
System.out.println(a.get("Jim"));
//Rome
a.put("Jim","The Rome");
System.out.println(a.get("Jim"));
//The Rome
System.out.println(a);
//{[Jim,The Rome], [Fred,Smith]}


}


it prints out

You entered an invalid key
Jim
You entered an invalid key
Jim

}

[pbrockway2]

If you want a collection that associates a value with some unique key use a Map. Sun's Tutorial has discussion and usage examples in the section The Map Interface.

Or is implementing this some sort of homework? If so - unless someone cares to do it for you - you would be best to work on just one piece of functionality at a time. If you get stuck post what you have and descriptions both of what it should do and what you observe it does do.

[emceenugget]

it's also probably better to use generics for the key and value.