Collections

官网api

Collections是一个非常实用的工具类，这里了解一下官网api里的方法

sort 实现对List类型的排序操作

public static <T> void sort(List<T> list, Comparator<? super T> c)

参数

• list - 要排序的list
• c - 可选 比较器，可以自定义比较方法

例子

Collections.sort(list, new Comparator<Point>(){
   	@Override
       public int compareTo(Point p1, Point p2){
       	return p1.x - p2.x;
       }
   })

binarySearch 二分查找

public static <T> int binarySearch(List<? extends T> list,
                   T key,
                   Comparator<? super T> c)

参数

• list - the list to be searched.
• key - the key to be searched for.
• c - the comparator by which the list is ordered. A null value indicates that the elements’ natural ordering should be used.

返回

如果找到，返回从0开始的下标>=0，否则返回 -(insertion point)-1

reverse 翻转list

public static void reverse(List<?> list)

shuffle

public static void shuffle(List<?> list, Random rnd))

swap 交换下标对应元素

public static void swap(List<?> list, int i, int j)

fill 把list全部修改成同一个值

public static <T> void fill(List<? super T> list,T obj)

copy

public static <T> void copy(List<? super T> dest, List<? extends T> src)

min&max

public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll)

rotate

public static void rotate(List<?> list, int distance)

replaceAll

public static <T> boolean replaceAll(List<T> list,
                     T oldVal,
                     T newVal)

indexOfSubList lastIndexOfSubList

public static int indexOfSubList(List<?> source,
                 List<?> target)

singleton

public static <T> Set<T> singleton(T o)

返回一个不可变的集合只包含指定对象。

一般可以配合removeAll使用，因为removeAll接受的参数是Set

例子

import java.util.*;

public class CollectionsDemo {
   public static void main(String args[]) {
      // create an array of string objs
      String init[] = { "One", "Two", "Three", "One", "Two", "Three" };
      
      // create two lists
      List list1 = new ArrayList(Arrays.asList(init));
      List list2 = new ArrayList(Arrays.asList(init));
      
      // remove from list1
      list1.remove("One");
      System.out.println("List1 value: "+list1);
      
      // remove from list2 using singleton
      list2.removeAll(Collections.singleton("One"));		   
      System.out.println("The SingletonList is :"+list2);
   }
}

List1 value: [Two, Three, One, Two, Three]
The SingletonList is :[Two, Three, Two, Three]

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