如何在java利用tostring方法实现重写

import java.util.*; public class TreeSetTest {      public static void main(String[] args) {     // TODO Auto-generated method stub     SortedSet<Item> parts=new TreeSet<Item>();     parts.add(new Item("Toaster", 1234));     parts.add(new Item("Widget", 4562));     parts.add(new Item("Modem", 9912));     System.out.println(parts);     SortedSet<Item> sortByDescription=new TreeSet<Item>(new          Comparator<Item>()         {           public int compare(Item a, Item b)           {             String descrA=a.getDescription();             String descrB=b.getDescription();             return descrA.compareTo(descrB);           }         });     sortByDescription.addAll(parts);     System.out.println(sortByDescription);   } } class Item implements Comparable<Item> {   public Item(String aDescription, int aPartNumber)   {     description=aDescription;     partNumber=aPartNumber;   }   public String getDescription()   {     return description;   }   public boolean equals(Object otherObject)   {     if(this==otherObject)       return true;     if(otherObject==null)     {       return false;     }     if (getClass()!=otherObject.getClass())     {       return false;     }     Item other=(Item)otherObject;     return description.equals(other.description)&&         partNumber==other.partNumber;   }   public int hashCode()   {     return 13*description.hashCode()+17*partNumber;   }   public int compareTo(Item other)   {     return partNumber-other.partNumber;   }   private String description;   private int partNumber; }