collectiontest.java

孙鑫JAVA从入门到精通配套练习程序。所有程序都实际运行过

//演示集合类的用法
import java.util.*;
class CollectionTest
{
	public static void printElements(Collection c)
	{
		System.out.println("Elements in collection as follows:");
		Iterator it = c.iterator();
		while(it.hasNext())
		{
			System.out.println(it.next());
		}
	}
	public static void main(String[] args)
	{
		/*
		ArrayList al = new ArrayList();
		al.add(new Point(1, 1));
		al.add(new Point(2, 2));
		al.add(new Point(3, 3));
		//for (int i=0; i<al.size(); i++)
		//{
		System.out.println(al);
		//}
		Object[] objs = al.toArray();
		for (int i=0; i<objs.length; i++)
		{
			System.out.println(objs[i]);
		}
		List l = Arrays.asList(objs);		//返回一个固定的列表
		System.out.println(l);
		printElements(al);
		
		//迭代器用法
		/*
		Iterator it = al.iterator();
		while(it.hasNext())
		{
			System.out.println(it.next());
		}
		*/
		
		ArrayList al = new ArrayList();
		Student s1 = new Student(2, "zhangshan");
		Student s2 = new Student(1, "lisi");
		Student s3 = new Student(3, "wangwu");
		Student s4 = new Student(2, "mybole");
		al.add(s1);
		al.add(s2);
		al.add(s3);
		al.add(s4);
		//Collections.sort(al, new Student.StudentCmp());
		Collections.sort(al, Collections.reverseOrder());
		printElements(al);
	}
}

class Point
{
	int x,y;
	Point(int x, int y)
	{
		this.x = x;
		this.y = y;
	}
	public String toString()
	{
		return "x=" + x + ", y=" + y;
	}
}

class Student implements Comparable
{
	int num;
	String name;
	Student(int num, String name)
	{
		this.num = num;
		this.name = name;
	}
	//使用内部类构造一个比较器（总与特定的类相关）
	static class StudentCmp implements Comparator
	{
		public int compare(Object o1, Object o2)
		{
			System.out.println("Compare");
			int result;
			Student s1 = (Student)o1;
			Student s2 = (Student)o2;
			result = s1.num > s2.num ? 1 : (s1.num == s2.num ? 0 : -1);
			//如果学号相等，则按名字排序
			if (0 == result)		
			{
				result = s1.name.compareTo(s2.name);
			}
			return result;
			
			
		}
	}
	
	public int compareTo(Object o)
	{
		System.out.println("Compareto");
		Student s = (Student)o;
		return num > s.num ? 1 : (num == s.num ? 0 : -1);
	}
	
	public String toString()
	{
		return num + ": " + name;
	}
}