java uses unsafe operations error in hashmap and arraylist

November 8, 2021

I was hoping to get a quick hand I have never encountered this error before. I think it is something in this part of my code but not sure :

public class ePortfolio {
protected HashMap <String,ArrayList<Integer>>map;
protected ArrayList <investment>list;
public ePortfolio(){
    list=new ArrayList();
    map= new HashMap();        
}

if there is anything more I need to add ill be happy to just don’t want to clutter the page .

>Solution :

I’ll guess as you’ve not given much detail:

The problem is that you are assigning a raw object, new ArrayList() to a genericized reference variable, ArrayList <investment> list.

You should instead let the compiler infer the generic parameters of your collection objects. Insert the empty angle-brackets <>.

public class ePortfolio {
    protected HashMap < String , ArrayList < Integer > > map ;
    protected ArrayList < Investment > list ;

    // Constructor
    public ePortfolio(){
        list = new ArrayList<>() ;  // ☚ Insert empty angles to ask compiler to infer the parameterized type. 
        map = new HashMap<>() ;        
    }

By the way, it is usually best to refer to the most general type that meets your needs. This way you can later swap out the more specific concrete type without breaking any code.

So if Map and List meet your needs, use those.

public class ePortfolio {
    protected Map < String , List < Integer > > map ;
    protected List < Investment > list ;

    // Constructor
    public ePortfolio(){
        list = new ArrayList<>() ;  // ☚ Insert empty angles to ask compiler to infer the parameterized type. 
        map = new HashMap<>() ;        
    }

As commented, see What is a raw type and why shouldn’t we use it?. And see tutorial on Generics by Oracle.