List collection of elements to weight in several ways

Disclaimer: This article is a blogger original article, shall not be reproduced without the bloggers allowed. https://blog.csdn.net/shy415502155/article/details/88554745

List collection features:

1 is an underlying array data structure.

2 is due to the nature of the array, a random access is achieved, and faster, holding data elements in accordance with the order of insertion.

3 lower delete and move elements of performance, because it will lead to move the entire collection of elements.

4 elements of the collection can be repeated.

5 sequential.

6 thread-safe

---

Create a collection and add elements

List<Integer> list = new ArrayList<Integer>();
list.add(100);
list.add(200);
list.add(300);
list.add(300);
list.add(400);
list.add(600);
list.add(500);
list.add(700);
list.add(600);

1. The first embodiment: the use of a collection set

list = new ArrayList<Integer>(new LinkedHashSet<Integer>(list));
System.out.println("去重复 未排序 ：" + list);

2. Using the method contains

List<Integer> withoutList = new ArrayList<Integer>();
if (list != null && list.size() > 0) {
    for (int i = 0; i < list.size(); i++) {
        if (!withoutList.contains(list.get(i))) {
            withoutList.add(list.get(i));
		}
	}
}
System.out.println("去重复 未排序 ：" + withoutList);
Collections.sort(withoutList);
System.out.println("去重复 已排序 ：" + withoutList);

3. Using the equals method

if (list != null && list.size() > 0) {
	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);
			}
		}
	}
}
System.out.println("去重复 未排序 ：" + list);

4. Use Collections.frequency (List, "value") value in the method of the number of List

List<Integer> withoutList = new ArrayList<Integer>();
for (Integer l : list) {
	if (Collections.frequency(withoutList, l) < 1) {
		withoutList.add(l);
	}
}
System.out.println("去重复 未排序 ：" + withoutList);

result:

Undeduplicated: [100, 200, 300, 300, 400, 600, 500, 700, 600]
deduplication unsorted: [100, 200, 300, 400, 600, 500, 700]
deduplication sorted: [100 , 200, 300, 400, 500, 600, 700]