Java集合概述

import java.util.*;

//类A的equals方法总是返回true,但没有重写其hashCode()方法
class A
{
	public boolean equals(Object obj)
	{
		return true;
	}
}
//类B的hashCode()方法总是返回1,但没有重写其equals()方法
class B
{
	public int hashCode()
	{
		return 1;
	}
}
//类C的hashCode()方法总是返回2,但没有重写其equals()方法
class C
{
	public int hashCode()
	{
		return 2;
	}
	public boolean equals(Object obj)
	{
		return true;
	}
}
public class TestHashSet
{
	public static void main(String[] args) 
	{
		HashSet books = new HashSet();
		//分别向books集合中添加2个A对象，2个B对象，2个C对象
		books.add(new A());
		books.add(new A());
		books.add(new B());
		books.add(new B());
		books.add(new C());
		books.add(new C());
		System.out.println(books);
	}
}

import java.util.*;


public class TestLinkedHashSet
{
	public static void main(String[] args) 
	{
		LinkedHashSet books = new LinkedHashSet();
		books.add("第一个");
		books.add("第二个");
		//删除 Struts2权威指南
		books.remove("第一个");
		//重新添加 Struts2权威指南
		books.add("第一个");
		System.out.println(books);//[第二个, 第一个]
	}
}

import java.util.*;

class R implements Comparable
{
	int count;
	public R(int count)
	{
		this.count = count;
	}
	public String toString()
	{
		return "R(count属性:" + count + ")";
	}
	public boolean equals(Object obj)
	{
		if (obj instanceof R)
		{
			R r = (R)obj;
			if (r.count == this.count)
			{
				return true;
			}
		}
		return false;
	}
	public int compareTo(Object obj)
	{
		R r = (R)obj;
		if (this.count > r.count)
		{
			return 1;
		}
		else if (this.count == r.count)
		{
			return 0;
		}
		else
		{
			return -1;
		}
	}
}
public class TestTreeSet2
{
	public static void main(String[] args) 
	{
		TreeSet ts = new TreeSet();
		ts.add(new R(5));
		ts.add(new R(-3));
		ts.add(new R(9));
		ts.add(new R(-2));
		//打印TreeSet集合，集合元素是有序排列的
		System.out.println(ts);
		//取出第一个元素
		R first = (R)ts.first();
		//为第一个元素的count属性赋值
		first.count = 20;
		//取出最后一个元素
		R last = (R)ts.last();
		//为最后一个元素的count属性赋值，与倒数第二个元素count属性相同
		last.count = -2;
		//再次输出count将看到TreeSet里的元素处于无序状态，且有重复元素
		System.out.println(ts);
		//删除属性被改变的元素，删除失败
		ts.remove(new R(-2));
		System.out.println(ts);
		//删除属性没有改变的元素，删除成功
		ts.remove(new R(5));
                ts.remove(new R(20));
		System.out.println(ts);
	}
}

import java.util.*;

class M
{
	int age;
	public M(int age)
	{
		this.age = age;
	}
	public String toString(){
	   return "M age:"+age;
	}
}

public class TestTreeSet3
{
	public static void main(String[] args) 
	{
		TreeSet ts = new TreeSet(new Comparator()
		{
			public int compare(Object o1, Object o2)
			{
				/*int age1 = o1 instanceof M ? ((M)o1).age :((N)o1).age;
				int age2 = o1 instanceof M ? ((M)o2).age :((N)o2).age;
				return age1 - age2;*/

				
				M m1 = (M)o1;
				M m2 = (M)o2;

				if (m1.age > m2.age)
				{
					return -1;
				}
				else if (m1.age == m2.age)
				{
					return 0;
				}
				else
				{
					return 1;
				}
				
			}
		});	
		ts.add(new M(5));
		ts.add(new M(-3));
		ts.add(new M(9));
		System.out.println(ts);//[M age:9, M age:5, M age:-3]
	}
}