COS126

• Download PList.java

/******************************************************************************
  *  Name:
  *  NetID:
  *  Precept:
  * 
  *  PList - Popularity List: Stack Version
  *          list where the most recently accessed or added entry
  *          is always on top.
  *          
  *  Dependencies: Entry, Stack, StdOut
  *****************************************************************************/

public class PList {
    // instance variables
    private Stack<Entry> list;       // stack of entries holds the whole list
    
    // constructor just initializes the empty list
    public PList() {
        list = new Stack<Entry>();
    }
    
    // add entry to top of list
    public void add(String name, String num) {
        Entry en = new Entry(name, num);
        list.push(en);
    }
    
    // output the list
    public void show() {
        if (list.isEmpty()) {
            StdOut.println("empty PList");
            return;
        }
        // not empty, output the list
        for (Entry en : list) {
            StdOut.println(en);
        }
    }
    
    // move entry with name to top of list, return number
    // return null if not there
    public String find(String name) {
        // need a temp stack to hold onto other entries
        Stack<Entry> temp = new Stack<Entry>();
        Entry found = null;
        
        // move everybody over to temp except your entry 
        while (!list.isEmpty()) {
            Entry en = list.pop();
            if (en.equals(name)) {
                // found it!  remember it.
                found = en;
            }
            // not right name.  save on temp and keep going
            else temp.push(en);
        }
        
        // replace list
        while (!temp.isEmpty()) {
            list.push(temp.pop());
        }
        
        // Did we find it?
        if (found == null) return null;
        
        // put found on top
        list.push(found);
        return found.getNum();
    }
    
    //remove and return Entry from list
    public Entry cut(String name) {
        // use find() to move Entry to top of list
        String found = find(name);
        if (found == null)
            throw new RuntimeException(name + "not found");
        // return Entry and remove it from list
        return list.pop();
    }
    
    // update num or add entry to list
    public void update(String name, String num) {
        // Is it already on list?
        String found = find(name);
        if (found != null) {
            // if there, cut it
            cut(name);    
        }
        // either way, add new version
        add(name, num);
        return;
    }
    
    // test main
    public static void main(String[] args) {
        PList list = new PList();
        list.add("Doug", "6092586314");
        list.add("Donna", "6092581978");
        list.add("Christopher", "6092585388");
        list.add("Maia", "6092586484");
        list.add("Chris", "6092582038");
        StdOut.println("Entire list:");
        list.show();
        StdOut.println("===========================");
        
        list.update("Maia", "6092588888");
        list.cut("Chris");
        StdOut.println("Doug " + list.find("Doug"));
        StdOut.println("Maria " + list.find("Maria"));
        StdOut.println("===========================");
        
        StdOut.println("Updated list:");
        list.show();
    }           
}