ArrayList, contains, objects

[Manuel Leiria]

Hi,

I receive an arraylist with several objects like this,

public class SomeObject{
  private final String name;
  private final int quantity;
  private final double value;
 
  public SomeObject(String name, int quantity, double value){
    this.name = name;
    this.quantity = quantity;
    this.value = value;
  }
  //getters
 
  public int hashcode{
    //code
  }
  //2 objects are equal if their names are equals
  public boolean equals(object obj){
    boolean result = false;
    if(obj instanceof SomeObject)
      result = this.name.equals(((SomeObject)obj).getName());
    return result;
  }
}
 
    

but my arraylist contains equal objects (same name but different quantities and values). What I want to do is create an ArrayList with the distinct objects but summing the quantities and values.

Example
What I have

 List list = new ArrayList();
SomeObject so = new SomeObject("SCO", 10, 10.1);
list.add(so);
SomeObject so = new SomeObject("SCO", 20, 10.2);
list.add(so);
SomeObject so = new SomeObject("SEF", 1, 1.1);
list.add(so);
//and so on...   

and I want to create a new ArrayList containing

  SomeObject("SCO", 30, 20.3);
SomeObject("SEF", 1, 1.1);  

Can you give some ideias?

thanks in advance,

[Vijayender Bandaru]

Assuming you have all the getX methods in SomeObject

CASE 1:

If you have control over SomeObject and if you can modify it,then the solution is very simple.

1.remove final modifier for all instance varialbles.
2.In the equals method,whenever the object names are equal
add up the current obj values with new object

 //2 objects are equal if their names are equals
  public boolean equals(Object obj){
    boolean result = false;
    if(obj instanceof SomeObject){
      result = this.name.equals(((SomeObject)obj).getName());
[B]      if(result){
      this.qty+=((SomeObject)obj).getQty();
          //similarly for the value
      }[/B]
     }
    return result;
  }

CASE 2: If you can't modify the SOmeObject class,here is the solution.

import java.util.*;
 
/**
 * @author Vijay
 */
public class SomeObjectTest {
 
public static void main(String[] args) {
 List list = new ArrayList();
 SomeObject so = new SomeObject("SCO", 10, 10.1);
 //list.add(so);
 addToList(list,so);
 SomeObject soNew = new SomeObject("SCO", 20, 10.2);
 //list.add(soNew);
 addToList(list,soNew);
 
}
 

/**
 * 
 * this method creates a new object by summing
 * up the values of Qty and values of object found
 * in the list to similar object (same name) to be added.
 *
 */

private static void addToList(List list,SomeObject soNew) {
// TODO Auto-generated method stub

 for(int i=0;i<list.size();i++){
 SomeObject soFromList=(SomeObject) list.get(i);
 if(soFromList.getName().equals(soNew.getName())){
 
 //since the instance variables of SomeObject are final,
 //the only thing you can do is remove already existing object
 list.remove(soFromList);
 String name=soNew.getName();
 int sumQty=soFromList.getQuantity()+soNew.getQuantity();
 double sumValue=soFromList.getValue()+soNew.getValue();;
 SomeObject soAfterSum = new SomeObject(name, sumQty, sumValue);
 list.add(soAfterSum);
 break;
 }
 }
}
}