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

问题描述

我已经这样创建了自己的自定义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.我尝试过此代码仅一次添加项目:

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")));
                                }

如果还尝试过此操作:

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")));
                                }

当我使用ArrayList或 ArrayList< Integer> 时，此代码有效，但是当我使用 ArrayList< Points>

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

有人可以向我解释如何避免重复我的清单吗?

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

推荐答案

正如您在注释中提到的Order无关紧要，我将使用 HashSet< String> 进行存储和检查 hood_name ，如果您想通过输入 hood_name 来获取 object ，则可以使用 HashMap< String，Point 代替，它返回对象在 O(1)时间.

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.

因此，您需要创建一个 HashSet< String> ，它将跟踪 ArrayList< Points> 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.                     
}

此外，如果只想使用 ArrayList< Point> 来执行此任务，则可以覆盖 equals(Object E)和 hashCode()类中的方法.有关更多信息，请参考此.

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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