ArrayList数组去重

ArrayList数组去重

• 1.LinkedHashSet
• 2.HashSet
• 3.steam的distinct()方法
• 4.steam的filter()方法
• 5.contains()方法
• 6.indexOf()方法
• 7.lastIndexOf()方法
• 8.双重for循环
• [9.sort 排序](#9.sort 排序)

运行结果

原数组 : [3, 3, 1, 2, 5, 6, 8, 6, 4, 2]
XXXXXX 去重后数组 : [3, 1, 2, 5, 6, 8, 4]

1.LinkedHashSet

List<Integer> list = new ArrayList<>(Arrays.asList(3, 3, 1, 2, 5, 6, 8, 6, 4, 2));
List<Integer> listByLinkedHashSet = new ArrayList<>(new LinkedHashSet<>(list));
System.out.println("原数组 : " + list);
System.out.println("LinkedHashSet 去重后数组 : " + listByLinkedHashSet);

2.HashSet

由于HashSet不能保证添加顺序，所以只能作为判断条件保证顺序

List<Integer> list = new ArrayList<>(Arrays.asList(3, 3, 1, 2, 5, 6, 8, 6, 4, 2));

HashSet<Integer> set = new HashSet<Integer>();
List<Integer> listByHashSet = new ArrayList<Integer>();
for (Integer num : list) {
    if (set.add(num)) {
        listByHashSet.add(num);
    }
}

System.out.println("原数组 : " + list);
System.out.println("HashSet 去重后数组 : " + listByHashSet);

如果不计较去重后的数据顺序，可以直接使用HashSet进行去重

HashSet hashSet = new HashSet<>(list);

List listByHashSet = new ArrayList<>(hashSet);

3.steam的distinct()方法

List<Integer> list = new ArrayList<>(Arrays.asList(3, 3, 1, 2, 5, 6, 8, 6, 4, 2));
List<Integer> listByStream = list.stream().distinct().collect(Collectors.toList());
System.out.println("原数组 : " + list);
System.out.println("Stream 去重后数组 : " + listByStream);

4.steam的filter()方法

List<Integer> list = new ArrayList<>(Arrays.asList(3, 3, 1, 2, 5, 6, 8, 6, 4, 2));

List<Integer> listByFilter = new ArrayList<>(list.size());
list.stream().filter(i -> {
    if (listByFilter.indexOf(i) == -1){
        listByFilter.add(i);
    }
    return false;
}).collect(Collectors.toList());

System.out.println("原数组 : " + list);
System.out.println("filter 去重后数组 : " + listByFilter);

5.contains()方法

List<Integer> list = new ArrayList<>(Arrays.asList(3, 3, 1, 2, 5, 6, 8, 6, 4, 2));

List<Integer> listByContains = new ArrayList<>(list.size());
for (Integer num : list) {
    if (!listByContains.contains(num)) {
        listByContains.add(num);
    }
}

System.out.println("原数组 : " + list);
System.out.println("Contains 去重后数组 : " + listByContains);

6.indexOf()方法

List<Integer> list = new ArrayList<>(Arrays.asList(3, 3, 1, 2, 5, 6, 8, 6, 4, 2));

List<Integer> listByIndexOf = new ArrayList<>(list.size());
for (int i = 0; i < list.size(); i++) {
    if (listByIndexOf.indexOf(list.get(i)) == -1){
        listByIndexOf.add(list.get(i));
    }
}

System.out.println("原数组 : " + list);
System.out.println("ForLoop 去重后数组 : " + listByIndexOf);

7.lastIndexOf()方法

List<Integer> list = new ArrayList<>(Arrays.asList(3, 3, 1, 2, 5, 6, 8, 6, 4, 2));
System.out.println("原数组 : " + list);

for (int i = 0; i < list.size(); i++) {
    if (list.indexOf(list.get(i)) != list.lastIndexOf(list.get(i))) {
        list.remove(list.lastIndexOf(list.get(i)));
    }
}

System.out.println("lastIndexOf 去重后数组 : " + list);

8.双重for循环

List<Integer> list = new ArrayList<>(Arrays.asList(3, 3, 1, 2, 5, 6, 8, 6, 4, 2));
System.out.println("原数组 : " + list);

for (int i = 0; i < list.size(); i++) {
    for (int j = i+1; j < list.size(); j++) {
        if(list.get(i)==list.get(j)) {
            list.remove(j);
        }
    }
}
System.out.println("ForLoop 去重后数组 : " + list);

9.sort 排序

排序之后，如果相邻两个元素是相等的，那么就说明重复了。（但这个方法会改变数组原有顺序）

List<Integer> list = new ArrayList<>(Arrays.asList(3, 3, 1, 2, 5, 6, 8, 6, 4, 2));
Collections.sort(list);

List<Integer> listBySort = new ArrayList<>(list.size());
listBySort.add(list.get(0));
for (int i = 1; i < list.size(); i++) {
    if (list.get(i-1) != list.get(i)) {
        listBySort.add(list.get(i));
    }
}

System.out.println("原数组 : " + list);
System.out.println("Sort 去重后数组 : " + listBySort);