java - get second array list without duplicates and add units from duplicates to single one -

package com.mkyong.util;  import java.io.bufferedreader; import java.io.filenotfoundexception; import java.io.filereader; import java.io.ioexception; import java.util.arraylist; import java.util.collections; import java.util.hashset; import java.util.list;  public class readfromcvs {      static arraylist<datas> datalist = new arraylist<datas>();      public static void main(string[] args) {          readfromcvs obj = new readfromcvs();         obj.run();         obj.printdatalist(readfromcvs.datalist);      }       public void run() {         string csvfile = "c:\\users\\user\\downloads\\salesdata.csv";         bufferedreader br = null;         string csvsplitby = ",";         string line = "";          try {             br = new bufferedreader(new filereader(csvfile));             br.readline();             while ((line = br.readline()) != null) {                  // split on comma                 string[] datas = line.split(csvsplitby);                              // crate data object store values                 datas dataobject = new datas();                  // add values csv file data object                 dataobject.setproductid(integer.parseint(datas[0]));                 dataobject.setunits(integer.parseint(datas[1]));                  // adding data object list                 datalist.add(dataobject);             }             // print values stored in datalist             collections.sort(datalist);          } catch (filenotfoundexception e) {             e.printstacktrace();         } catch (ioexception e) {             e.printstacktrace();         } {             if (br != null) {                 try {                     br.close();                 } catch (ioexception e) {                     e.printstacktrace();                 }             }         }     }      public void printdatalist(list<datas> datalisttoprint) {         (int = 0; < datalisttoprint.size(); i++) {             system.out.println("product id: " + datalisttoprint.get(i).getproductid() + " units: "                     + datalisttoprint.get(i).getunits());         }     } } 

class datas implements comparable<datas> {   private int productid;   private int units;    public int getproductid() {     return productid;   }    public void setproductid(int productid) {     this.productid = productid;   }    public int getunits() {     return units;   }    public void setunits(int units) {     this.units = units;   }    @override   public int compareto(datas d) {     if (this.getproductid() > d.getproductid()) {         return 1;     } else if (this.getproductid() < d.getproductid()) {         return -1;     } else {         return 0;     }  }   } 

i want move objects 1 array list 1 without duplicates when need add units duplicate product id single product id

here of out after sorting first arraylist:

product id: 10001 units: 5 product id: 10001 units: 8 product id: 10001 units: 7 product id: 10002 units: 4 product id: 10002 units: 10 product id: 10002 units: 6 product id: 10003 units: 8 product id: 10003 units: 6 product id: 10003 units: 3 product id: 10003 units: 7 product id: 10003 units: 4 product id: 10004 units: 6 product id: 10004 units: 9 product id: 10004 units: 3 product id: 10004 units: 7 

instead of list, might easier map. parse input file, store products in hashmap<integer,datas> productid. process new instances of datas input, check map see if have productid, , if so, update units of instance.

map<integer,datas> products = new hashmap<>(); ... // parse input file. each record: int productid = integer.parseint(record[0]); int units = integer.parseint(record[1]);  if (products.containskey(productid)) {     datas existingrecord = products.get(productid);     existingrecord.setunits(existingrecord.getunits() + units); } else {     datas d = new datas();     d.setproductid(productid);     d.setunits(units);     products.put(productid, d); } 

by way, datas class name not follow java conventions. capitalize first letter, , try name more meaningful. maybe product?