Java collections covariance problem

Question

Lets say we have a program which contains such classes:

public interface AbstractItem {
}
public SharpItem implements AbstractItem {
}
public BluntItem imple         


        

Answer 1

public interface AbstractItem
{
}
public class SharpItem implements AbstractItem
{
}
public class BluntItem implements AbstractItem
{
}

public interface AbstractToolbox
{
    public List getItems();
}
public class ExpensiveToolbox implements AbstractToolbox
{
    private List items = new ArrayList();
    public List getItems() { return this.items; }
}
public class CheapToolbox implements AbstractToolbox
{
    private List items = new ArrayList();
    public List getItems() { return this.items; }
}


public void doImportantStuff(AbstractToolbox toolbox)
{
    List items = toolbox.getItems();

    for(AbstractItem item : items) 
        ... ;

}