Java List去重多种常用方法

package springboot.activiti.demo.utils;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;

public class ListDemo {
	public static void main(String[] args) {

		List list = Arrays.asList("aa", "bb", "cc", "dd", "bb", "cc", "ee","aa");
		
		/**
		 * 调用Arrays.asList()生产的List的add、remove方法时报异常，这是由Arrays.asList() 返回的市Arrays的内部类ArrayList， 
		 * 而不是java.util.ArrayList。Arrays的内部类ArrayList和java.util.ArrayList都是继承AbstractList，
		 * remove、add等方法AbstractList中是默认throw UnsupportedOperationException而且不作任何操作。
		 * java.util.ArrayList重新了这些方法而Arrays的内部类ArrayList没有重新，所以会抛出异常。
		 */
		list=new ArrayList<>(list);//重新new 一次
		
		// 去重1
		List removeDuplication = removeDuplication(list);
		System.out.println(removeDuplication.toString());
		//去重2
		List removeDuplication2 = removeDuplication2(list);
		System.out.println(removeDuplication2.toString());
		//去重3
		List removeDuplication3 = removeDuplication3(list);
		System.out.println(removeDuplication3.toString());
		//去重3
		List removeDuplication4 = removeDuplication4(list);
		System.out.println(removeDuplication4.toString());
       	//Java8的写法
		 List newList = list.stream().distinct().collect(Collectors.toList());
		 System.out.println(newList.toString());
	}

	// 去重1：遍历循环
	public static List removeDuplication(List list) {
		for (int i = 0; i < list.size() - 1; i++) {
			for (int j = list.size() - 1; j > i; j--) {
				if (list.get(j).equals(list.get(i))) {
					list.remove(j);
				}
			}
		}
		return list;
	}
	
	//遍历判断是否包含
	public static List  removeDuplication2(List list) {
	    List result = new ArrayList(list.size());
	    for (String str : list) {
	        if (!result.contains(str)) {
	            result.add(str);
	        }
	    }
	    list.clear();
	    list.addAll(result);
	    return list;
	}
	
	//利用HashSet不能添加重复数据的特性,HashSet不能保证添加顺序
	public static List removeDuplication3(List list) {
	    HashSet set = new HashSet(list.size());
	    List result = new ArrayList(list.size());
	    for (String str : list) {
	        if (set.add(str)) {
	            result.add(str);
	        }
	    }
	    list.clear();
	    list.addAll(result);
	    return list;
	}
	
	//LinkedHashSet 去重，保证顺序
	public static List removeDuplication4(List list) {
	    LinkedHashSet set = new LinkedHashSet(list.size());
	    set.addAll(list);
	    list.clear();
	    list.addAll(set);
	    return list;
	}

}