Java收集工具Collections

Java 提供了一个工具类，用于操作 Set、List、Map 等集合：Collections。该工具类提供了大量对集合元素进行排序、查询和修改的方法。它还提供了对集合对象进行同步控制的方法。常用方法：

example:
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class CollectionsTest {
public static void main(String[] args) {
	//Create a List collection of Integer type
	List<Integer> list = new ArrayList<>();
	//Add data to it
	list.add(1);
	list.add(2);
	list.add(3);
	list.add(4);
	list.add(5);
	list.add(3);
	list.add(4);
	list.add(5);
	//Print collection
System.out.println("--------------Collection------------------");
	System.out.println(list);//[1, 2, 3, 4, 5, 3, 4, 5]
	System.out.println("--------------reverse------------------");
	Collections.reverse(list);//Reverse sort
	System.out.println(list);//[5, 4, 3, 5, 4, 3, 2, 1]
	System.out.println("--------------shuffle------------------");
	Collections.shuffle(list);//Shuffle the order randomly
	System.out.println(list);//[3, 4, 1, 5, 5, 4, 3, 2]
	System.out.println("--------------sort------------------");
	Collections.sort(list);//Naturally sort, sort the list in ascending order
	System.out.println(list);//[1, 2, 3, 3, 4, 4, 5, 5]
	System.out.println("--------------sort(List list,Comparator c)------------------");
	//Sort the specified list according to the order generated by the specified comparator
	Collections.sort(list, new Comparator<Integer>() {
		@Override 
		public int compare(Integer o1, Integer o2) {
			//TODO Auto-generated method stub
			return o2-o1;//Descending order
		}
	});
	System.out.println(list);//[5, 5, 4, 4, 3, 3, 2, 1]
	System.out.println("--------------swap------------------");
	Collections.swap(list, 0, 7);//Swap 0 and 7 indexed elements
	System.out.println(list);//[1, 5, 4, 4, 3, 3, 2, 5]
	System.out.println("--------------rotate------------------");
	Collections.rotate(list, 2);//Move back 2 positions
	System.out.println(list);//[2, 5, 1, 5, 4, 4, 3, 3]
	System.out.println("--------------binarySearch------------------");
	//Find the index for the value in the parentheses
	System.out.println(Collections.binarySearch(list, 5));//3
	System.out.println("--------------max min------------------");
	System.out.println(Collections.max(list));//5 maximum
	System.out.println(Collections.min(list));//1 minimum
	//fill  
	System.out.println("--------------fill------------------");
//Collections.fill(list,0);//Replace all elements
	System.out.println(list);//[0, 0, 0, 0, 0, 0, 0, 0]
	System.out.println("--------------frequency------------------");
	//Return the number of given elements
	System.out.println(Collections.frequency(list,5));//2
	System.out.println("--------------indexOfSubList, lastIndexOfSubList------------------");
	List<Integer> list2 = new ArrayList<Integer>();
	list2.add(1);
	list2.add(5);
	//If there is a piece of list2 data in the list collection, there is an index return
	System.out.println(Collections.indexOfSubList(list, list2));//2 first
	System.out.println(Collections.lastIndexOfSubList(list, list2));//2 last
	//replaceAll replace all 5 to 0
	System.out.println("--------------replaceAll------------------");
	Collections.replaceAll(list, 5, 0);
	System.out.println(list);
}
}

结果如下：

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