如何在Java中将键添加为Integer并且值为arraylist的HashMap中添加元素？

Question

I am a writing a class that whose constructor takes an List<String> and returns a hashmap having length of string as key(Integer) and its value as arrayList<String> that holds string. That is I am trying to map length of strings to list of strings. Here is my code.

public class Solver {
   Map<Integer,ArrayList<String>> inventoryMap;

    //constructor
    public Solver(List<String> list){
    inventoryMap=new HashMap<Integer,ArrayList<String>>();
    for (String s : list) {
         int x = s.length();
         if (inventoryMap.containsKey(x)){
            inventoryMap.put(x,inventoryMap.get(x).add(s));
         } else {
            newlist=new ArrayList<String>();
            newlist.add(s);
            inventoryMap.put(x,newlist);
         }
      }
   }

when I complile this code, I get the following error

Solver.java:12: put(java.lang.Integer,java.util.ArrayList<java.lang.String>) in java.util.Map<java.lang.Integer,java.util.ArrayList<java.lang.String>> cannot be applied to (int,boolean)
            inventoryMap.put(x,inventoryMap.get(x).add(s));

I think I am going wrong in adding String elements to my ArrayList<String> which is value of Map can you guide me with what I could possibly be going wrong?

Answer 1

if (inventoryMap.containsKey(x)) {
     inventoryMap.put(x,inventoryMap.get(x).add(s));
} 

Change this with

if (inventoryMap.containsKey(x)) {
    inventoryMap.get(x).add(s);
} 

Reason is inventoryMap.get(x).add(s) will return boolean so you cann't put boolean in place of List.

As map already contains list so adding any element in a list you need not to put any entry in a map. Just get the list from map and add element to it.

Answer 2

inventoryMap.get(x).add(s) returns boolean and you tried to put it in the map. This is the cause of the exception. Put the list in the map will resolve the issue.

Answer 3

Your code inventoryMap.get(x).add(s) adds the value to the list and return a boolean. So You need to have something like.

List<String> list =inventoryMap.get(x);
list.add(s);

Answer 4

You cannot chain your method calls like inventoryMap.put(x,inventoryMap.get(x).add(s)) since add returns a boolean . As a matter of fact, you don't even need the put statement. Since you aren't remove ing the List , its reference will stay in the Map so any updates to the List will be visible.

All you need is inventoryMap.get(x).add(s) .

Answer 5

First of all inventoryMap.get(x).add(s) returns boolean (whether elements where successfully added or not ). So is incompatible with the type ArrayList<String> . You can simple do

inventoryMap.get(x).add(s)

No need to explicitly call pur() function.

Secondly int x = s.length(); should be Integer x = s.length(); . You can put int where Integer is expected(anyways you cannot use int in generics).

Answer 6

The problem with this line

        inventoryMap.put(x,inventoryMap.get(x).add(s));

is that inventoryMap.get(x).add(s) will return a boolean and map expects a List here. You need to break down this statement. something like this:

List<String> stirngsList = inventoryMap.get(x);
stirngsList.add(s);