TreeSet小例

 

package com.test.collframework;

import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;

/**
 * TreeSet是一个有序集合 
 */
public class TreeSetTest {

	public static void main(String[] args) {
		Set<Item> set = new TreeSet<Item>();
		set.add(new Item("Toaster",1234));
		set.add(new Item("Widget",4562));
		set.add(new Item("Modem",9912));
		System.out.println(set);
		
		Set<Item> sortByDescription = new TreeSet<Item>(new
			Comparator<Item>() { //添加一个比较器
				public int compare(Item a, Item b) {
					String aDes = a.getDescription();
					String bDes = b.getDescription();
					return aDes.compareTo(bDes);
				}
			}
		); 
		sortByDescription.addAll(set);
		System.out.println(sortByDescription);
	}
	
}

class Item implements Comparable<Item> {//Item类实现Comparable

	private String description;
	private int partNumber;

	public Item(String aDescription, int aPartNumber) {
		this.description = aDescription;
		this.partNumber = aPartNumber;
	}

	public String getDescription() {
		return description;
	}

	public boolean equals(Object otherObj) {
		if(this == otherObj){
			return true;
		}
		if(otherObj == null){
			return false;
		}
		if(this.getClass() != otherObj.getClass()){
			return false;
		}
		Item otherItem = (Item) otherObj;
		return description.equals(this.getDescription()) && partNumber == otherItem.partNumber;
	}
	
	public int hashCode() {
		return 13*description.hashCode() + 17*partNumber;
	}
	
	public String toString() {
		return "[description =" + description + "],[partNumber =" + partNumber + "]";
	}
	
	public int compareTo(Item other) { //使用partNumber做比较
		return partNumber - other.partNumber;
	}

}

打印结果

 [[description =Toaster],[partNumber =1234], [description =Widget],[partNumber =4562], [description =Modem],[partNumber =9912]]

 

[[description =Modem],[partNumber =9912], [description =Toaster],[partNumber =1234], [description =Widget],[partNumber =4562]]