在自定义 ArrayList 中只添加一次项目 [英] Add item only once in custom ArrayList

问题描述

我像这样制作了自己的自定义 ArrayList:

I've made my own custom ArrayList like this:

public class Points {
    String hoodName;
    Double points;
    Integer hoodId;
    public Points(String hN, Double p, Integer hI){
        hoodName = hN;
        points =p;
        hoodId = hI;
    }

    public Double getPoints() {
        return points;
    }

    public Integer getHoodId() {
        return hoodId;
    }

    public String getHoodName() {
        return hoodName;
    }
}

当我从 JSON api 添加数据时，它会多次添加项目.我试过这个代码只添加一次项目:

When I'm adding data from my JSON api it adds item multiple times. I've tried this code to add the items only once it:

if (!points.contains(jsonObject.getString("hood_name"))) {
                                    points.add(new Points(jsonObject.getString("hood_name"), jsonObject.getDouble("points"), jsonObject.getInt("hood_id")));
                                }

如果也试过这个:

if (!points.contains(Points(jsonObject.getString("hood_name"), jsonObject.getDouble("points"), jsonObject.getInt("hood_id")))) {
                                    points.add(new Points(jsonObject.getString("hood_name"), jsonObject.getDouble("points"), jsonObject.getInt("hood_id")));
                                }

此代码在我使用 ArrayList 或 ArrayList 时有效，但在我使用 ArrayList

This code is working when I use a ArrayList or ArrayList<Integer> but not when I'm using ArrayList<Points>

谁能解释我如何避免列表中的重复?

Can anyone explain me how I can avoid duplication in my list?

推荐答案

正如你在评论中提到的 Order 无关紧要，我会有一个 HashSet 来存储和检查hood_name 并且如果你想通过输入 hood_name 来获取 object 你可以使用 HashMap 而不是它返回O(1) 时间内的对象.

As you mentioned in the comments that Order doesn't matter , I would have an HashSet<String> to store and check the hood_nameand If you want to get object by entering hood_name you can use HashMap<String,Point instead which returns the object in O(1) time.

所以你需要创建一个HashSet，它将跟踪ArrayList中存在的所有对象的hood_name.

So You need to create a HashSet<String> which will keep track of hood_name of all objects present in the ArrayList<Points>.

HashSet<String> all_ids=new HashSet<String>();

if (!all_ids.contains(jsonObject.getString("hood_name"))) 
{
    points.add(new Points(jsonObject.getString("hood_name"), jsonObject.getDouble("points"), jsonObject.getInt("hood_id")));
    all_ids.add(jsonObject.getString("hood_name")); //You need to add it to set as Now it exists in the list.                     
}

另外，如果你只想使用ArrayList来执行这个任务，你可以重写equals(Object E)和hashCode()Point 类中的 方法.有关详细信息，请参阅此.

Further more , If you want to only use ArrayList<Point> to execute this task , You can override equals(Object E) and hashCode() methods in Point class. For more information , refer this.

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