HELP?! a class that implements ..... : java.util.Vector

Question

My instructions say this:
In the constructor, create the collection object (Since java.util.List is an interface, you will need to instantiate a class that implements this interface: java.util.Vector or java.util.LinkedList or java.util.ArrayList).
I know, this IS a homework assignment - I am not sure how to go about this. I DO have code so far up to this point, can anyone help?
import dLibrary.*;
import java.awt.Color;
* @author Rob
* @version 8/18/03
public class PhrasesII extends A3ButtonHandler
        private A3ButtonWindow win;
        private ATextField stringAcceptor;
        private ALabel listOstrings;
        private ALabel inputString;
        private ALabel status;
        private java.awt.List display;
        private java.util.List collection;
public PhrasesII()
        win = new A3ButtonWindow(this);
        stringAcceptor= new ATextField (50,420,200,25);
        stringAcceptor.place(win);
        listOstrings = new ALabel(100, 10, 100, 380);
        listOstrings.setFontSize(10);
        listOstrings.setText("List of Strings:");
        listOstrings.place(win);
        inputString = new ALabel(50,400,200,25);
        inputString.setFontSize(10);
        inputString.setText("Input String:");
        inputString.place(win);
        display = new java.awt.List();
        display.setLocation(200, 100);
        display.setSize(200, 250);
        display.setBackground(Color.lightGray);
        win.add(display, 0);
        win.setLeftText("Save");
        win.setMidText("Display");
        win.setRightText("Discard");
        win.repaint();
  public void leftAction()
    public void midAction()
    public void rightAction()

Answer 1

I am getting a " can't resolve symbol" when I do thisYou have to either import java.util.ArrayList or specify it fully, e.g., "new java.util.ArrayList()".
Is that the line that is causing you problems? The error message should give the line number.
my instructions also say I have to use "interface
java.util.List when declaring your reference" so I am
confused about using "= new ArrayList();"What they're saying is that you want code like this:
private java.util.List frogs;    // this is the reference declaration
//... later on...
frogs = new java.util.ArrayList();  // this isn't a declarationWhat this means is that when you declare a field or variable, you should declare its type to be an interface.
But when you actually instantiate a value for that variable, then you should use a concrete class that implements that interface. (You have to; interfaces can't be instantiated.)
This is good programming style for reasons I don't have the space to explain here.