Java中List去重-蒲公英云

Java中List去重

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
public class Test {
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        list.add("1001A410000000PS6PI3");
        list.add("1001A410000000PS6WK7");
        list.add("1001A410000000PS6PI3");
        list.add("1001A410000000PS6W77");
        System.out.println(removeDuplicate1(list));
//        System.out.println(removeDuplicate2(list));
//        System.out.println(removeDuplicate3(list));
//        System.out.println(removeDuplicate4(list));
//        System.out.println(removeDuplicate5(list));
    }
    /**
     * 方法一： Stream 去重：list.stream().distinct()
     * @param list
     * @return
     */
    private static List<String> removeDuplicate1(List<String> list) {
        List<String> newList = (List) list.stream().distinct().collect(Collectors.toList());
        return newList;
    }
    /**
     * 方法二：通过 HashSet 剔除重复元素(会改变原有顺序)
     * @param list
     * @return
     */
    private static List<String> removeDuplicate2(List<String> list) {
        Set<String> tempSet = new HashSet<String>(list);
        list.clear();
        list.addAll(tempSet);
        return list;
    }
    /**
     * 方法三：删除 ArrayList 中重复元素，保持顺序
     * @param list
     * @return
     */
    private static List<String> removeDuplicate3(List<String> list) {
        Set<String> tempSet = new HashSet<String>();
        List<String> newList = new ArrayList<>();
        for (Iterator iter = list.iterator(); iter.hasNext(); ) {
            String next = (String) iter.next();
            if (tempSet.add(next)) {
                newList.add(next);
            }
        }
        return newList;
    }
    /**
     * 方法四：遍历 list，用 tempList.contain()，不存在 add
     * @param list
     * @return
     */
    private static List<String> removeDuplicate4(List<String> list) {
        List<String> tempList = new ArrayList<>();
        for (int i = 0; i < list.size(); i++) {
            if (!tempList.contains(list.get(i))) {
                tempList.add(list.get(i));
            }
        }
        return tempList;
    }
    /**
     * 方法五：循环 list 中的所有元素然后删除重复(会改变原有顺序)
     * @param list
     * @return
     */
    private static List<String> removeDuplicate5(List<String> list) {
        for (int i = 0; i < list.size(); i++) {
            for (int j = list.size() - 1; j > i; j--) {
               if (list.get(i).equals(list.get(j))) {
                    list.remove(list.get(i));
                }
            }
        }
        return list;
    }
}