generic implementation for future flexibility

public class CollectionsRef {
    private HashSet<Integer> numbers;
    public ArrayList<String> getList() {
        return new ArrayList<String>();
    public void setNumbers(HashSet<Integer> numbers) {
        this.numbers = numbers;
Look at the reference types which are collection implementation classes - this locks the code to work with only these classes HashSet and ArrayList. What if we want the method getList() can return a LinkedList and the method setNumbers() can accept a TreeSet?
The above class can be improved by replace the class references to interface references like this:
public class CollectionsRef {
    private Set<Integer> numbers;
    public List<String> getList() {
        // can return any kind of List
     [b]   return new ArrayList<String>();[/b]
    public void setNumbers(Set<Integer> numbers) {
        // can accept any kind of Set
        this.numbers = numbers;

Open in new window

can we have generic List as return type to provide more flexibility to future changes to collection implementation?
Please advise
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mccarlIT Business Systems Analyst / Software DeveloperCommented:

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ste5anSenior DeveloperCommented:

Cause the reason for choosing the correct type is not "being future proof". This would be an wasted effort.

The reason for choosing a more generic type is that you're able to change between different kind of collections used in your implementation. This is part of polymorphism in OOP.
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