Come aggiungere un elemento a un arraylist che si trova in una hashmap

Ci vuole una mappa che ha come chiave la parola chiave dai dati csv e come valore una lista che contiene tutti i valori alternativi corrispondenti a una parola chiave.

1. Map> alternateMap = new HashMap<>(); 

Note that putting a value into a map with a key which is already present in that map will overwrite the previous value. So you have to put the list only the first time you find a new Keyword, i.e. when trying to add an alternative for a keyword, first check whether the corresponding List exists in the map, if not then create a List and put into the map, then add the Alternate to that list.

1. while(...) { 
2. String keyword = ...; 
3. String alternate = ...; 
4. // check whether the list for keyword is present 
5. List alternateList = alternateMap.get(keyword); 
6. if(alternateList == null) { 
7. alternateList = new ArrayList<>(); 
8. alternateMap.put(keyword, alternateList); 
9. } 
10. alternateList.add(alternate); 
11. } 
12.  
13. // printing the result 
14. for(Map.Entry> alternateEntry : alternateMap.entrySet()) { 
15. System.out.println(alternateEntry.getKey() + ": " +  
16. alternateEntry.getValue().toString()); 
17. } 

here ia complete code of mine i hope it will help you

package data;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.Iterator;

import java.util.Map;

public class ProductInventory

{

private Map > product;

private ArrayList buildProduct;

private ArrayList > addProduct;

public ProductInventory()

{

/** Set default values **/

product = new > HashMap();

buildProduct = new ArrayList ();

addProduct = new ArrayList> ();

/** START - Create ArrayList for each item and add to HashMap**/

ArrayList c1 = new ArrayList();

ArrayList c2 = new ArrayList();

c1.add("computer"); c1.add("Apple"); c1.add("iPad2"); c1.add("499.00");

c2.add("computer"); c2.add("Asus"); c2.add("Zenbook"); c2.add("1449.00");

ArrayList tv1 = new ArrayList();

ArrayList tv2 = new ArrayList();

tv1.add("television"); tv1.add("Panasonic"); tv1.add("Viera"); tv1.add("899.00");

tv2.add("television"); tv2.add("Samsung"); tv2.add("Series 6"); tv2.add("1597.00");

ArrayList a1 = new ArrayList();

ArrayList a2 = new ArrayList();

a1.add("audio"); a1.add("Bose"); a1.add("321 GS Series III"); a1.add("999.00");

a2.add("audio"); a2.add("Onkyo"); a2.add("HT-S3400"); a2.add("329.00");

/** END - Create ArrayList for each item and add to HashMap **/

/** Add entrys to HashMap **/

product.put("CMC769LLA",c1);

product.put("CUX31EDH72",c2);

product.put("TVTCL50E3",tv1);

product.put("TVUN55D6000",tv2);

product.put("A321GSIIIBK",a1);

product.put("AHTS3400",a2);

}

/** For the sake of this example, the productAttribute parameter will be equal to "computer" **/

public void setProducts(String productAttribute)

{

for (Map.Entry > entry : product.entrySet()) /** Loop through all entrys in the HashMap **/

{

for (String s: entry.getValue()) /** Loop through all values in HashMap**/

{

/** Add product attributes **/

if (s.equals(productAttribute)) /** Check to see if param exists in the value set**/

{

/** Add key to buildProduct ArrayList **/

buildProduct.add(entry.getKey());

/*Loop through values of the corresponding key and add to buildProduct*/

for (Iterator i = entry.getValue().iterator(); i.hasNext();)

{

Object item = i.next();

buildProduct.add(item.toString());

}

/** Add buildProduct arrayList to product arrayList **/

addProduct.add(buildProduct);

break; /** Exit nested loop**/

}

}

}

}

}