标签：poi 用法 排序 collect eve array 数组 引用类型 类型
一、基本介绍
1、List集合内的元素是有序的，能用下标获取的
2、List接口的两个常用实现类:ArrayList 和 LinkedList
3、一些常用方法:
get()、set()、add()、remove()、subList()
4、List和数组之间的转换:
a、List转换为数组:
b、数组转换为List:
/** * List转换为数组:toArray()方法 */ List<String> list = new ArrayList<String>(); list.add("one"); list.add("two"); list.add("three"); list.add("four"); System.out.println("原集合为:"+list); String[] array = list.toArray(new String[]{}); for(String str:array){ System.out.println(str); } /** * 数组转换为List: Arrays.asList()方法 */ String[] array1 = {"five","six","seven","eight"}; List<String> list1 = Arrays.asList(array1); System.out.println(list1); }
5、List的排序功能:
(1)自然排序(从小到大):
/** * List的自然排序 */ List<Integer> list = new ArrayList<Integer>(); Random ran = new Random(); for(int i=0;i<10;i++){ list.add(i,ran.nextInt(100)); } System.out.println("原集合为:"+list); Collections.sort(list); System.out.println("自然排序后的集合为:"+list);
(2)引用类型的排序(两种实现方法):
a、Comparable:引用元素必须是Comparable的子类
package Java20170330; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; class Point implements Comparable<Point>{ int x; int y; public Point(int x, int y) { super(); this.x = x; this.y = y; } public String toString() { return "("+x + "," + y +")"; } public int compareTo(Point p){ return (int) (Math.sqrt(this.x*this.x+this.y*this.y)-Math.sqrt(p.x*p.x-p.y*p.y)); } } public class Blogtest01 { public static void main(String[] args) { List<Point> list = new ArrayList<Point>(); list.add(new Point(3,3)); list.add(new Point(1,4)); list.add(new Point(4,3)); list.add(new Point(2,5)); Collections.sort(list); System.out.println("排序后的集合为:"+list); } }
运行结果为:
排序后的集合为:[(3,3), (1,4), (4,3), (2,5)]
b、Comparator : 适用于临时指定比较规则
Demo1:
package Java20170330; import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.List; public class Blogtest { public static void main(String[] args) { List<String> list = new ArrayList<String>(); list.add("cnmgb"); list.add("nmb"); list.add("nmgb"); list.add("nm"); System.out.println("原集合为:"+list); Collections.sort(list,new Comparator<String>(){ public int compare(String str1,String str2){ return str1.length()-str2.length(); } }); System.out.println("排序后的集合为:"+list); } }
运行结果为:
原集合为:[cnmgb, nmb, nmgb, nm]
排序后的集合为:[nm, nmb, nmgb, cnmgb]
Demo2:
package Java20170330; import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.List; class Point{ int x; int y; public Point(int x, int y) { super(); this.x = x; this.y = y; } @Override public String toString() { return "(" + x + "," + y + ")"; } } public class Blogtest { public static void main(String[] args) { List<Point> list = new ArrayList<Point>(); list.add(new Point(3,3)); list.add(new Point(1,4)); list.add(new Point(4,3)); list.add(new Point(2,5)); System.out.println("原集合为:"+list); Collections.sort(list,new Comparator<Point>(){ public int compare(Point p1,Point p2){
return (int) (Math.sqrt(p1.x*p1.x+p1.y*p1.y)-Math.sqrt(p2.x*p2.x-p2.y*p2.y));
}
});
System.out.println("排序后的集合为:"+list);
}
运行结果为:
原集合为:[(3,3), (1,4), (4,3), (2,5)]
排序后的集合为:[(3,3), (1,4), (4,3), (2,5)]
标签：poi 用法 排序 collect eve array 数组 引用类型 类型
原文地址：http://www.cnblogs.com/codeyuan1992/p/6644310.html
