Java ArrayList 检查数据是否已经存在
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ArrayList check if data already exists
提问by Oreo
Just want to check if data already exist(s) or not in ArrayList, but everytime getting : Not Exist(s) whereas data exists in ArrayList, and as a result i am getting duplicate records in a list..
只是想检查数据是否已经存在于 ArrayList 中，但每次获取：不存在而数据存在于 ArrayList 中，因此我在列表中获取重复记录..
DataArrayList.secondArraylist.add(new Second(actorList.get(position).getName(), actorList.get(position).getImage()));
System.out.println(DataArrayList.secondArraylist.size());
String strName = actorList.get(position).getName().toString();
Log.d("name:", strName);
for(int i=0; i<DataArrayList.secondArraylist.size(); i++)
{
if(DataArrayList.secondArraylist.get(i).getName().equals(strName)) {
System.out.println(DataArrayList.secondArraylist.get(i).getName());
Toast.makeText(context, "Exist(s)", Toast.LENGTH_SHORT);
}
else {
Toast.makeText(context, "Not Exist(s)", Toast.LENGTH_SHORT);
}
}
Problem:
问题：
Not getting any Toast message, which i am using to indicate that "Data Exists" or "Not"
没有收到任何 Toast 消息，我用它来表示“数据存在”或“不存在”
Finally:
最后：
I would like to add item to arraylist if already not exist(s), else want to show Toast that item already exist(s)
如果不存在，我想将项目添加到数组列表，否则想向 Toast 显示该项目已经存在
采纳答案by pathfinderelite
You are comparing your list object DataArrayList.secondArraylistwith a String
您正在将列表对象DataArrayList.secondArraylist与String
if (DataArrayList.secondArraylist.equals(strName)) {
That will always return false. Instead, create a method that loops through the list and checks the strNameagainst the name of the Secondobjects that are stored in the list.
那总会回来的false。相反，创建一个循环遍历列表的方法，并strName根据Second存储在列表中的对象的名称检查。
boolean contains(ArrayList<Second> list, String name) {
for (Second item : list) {
if (item.getName().equals(name)) {
return true;
}
}
return false;
}
Then use it
然后使用它
if (contains(DataArrayList.secondArraylist, strName)) {
System.out.println("Data Exist(s)");
} else {
System.out.println("Not Exist(s)");
}
回答by Md. Nasir Uddin Bhuiyan
You need to use indexOf()while checking a value in ArrayList
您需要indexOf()在检查 ArrayList 中的值时使用
if (DataArrayList.secondArraylist.indexOf(strName)!=-1) {
System.out.println("Data Exist(s)");
} else {
System.out.println("Not Exist(s)");
}
回答by Gisonrg
As the strNameyou are checking is a property of your Object Second, you cannot check it directly using method of the ArrayList. The easiest way would be loop through the ArrayList DataArrayList.secondArraylist, get each Secondobject contained in the list, then check if strNameis equal to that property of your Secondobject.
由于strName您正在检查的是 Object 的一个属性Second，因此您不能直接使用 的方法检查它ArrayList。最简单的方法是遍历 ArrayList DataArrayList.secondArraylist，获取Second列表中包含的每个对象，然后检查是否strName等于Second对象的该属性。
Not sure how you implement the Secondobject, but you should get the corresponding String from each Secondobject then compare it with the strName.
不确定您如何实现该Second对象，但您应该从每个Second对象中获取相应的 String，然后将其与strName.
回答by SweetWisher ツ
The contains method calls the equals method with signature equals(Object), so you requires to override this method in your POJO class.
contains 方法调用具有签名 equals(Object) 的 equals 方法，因此您需要在 POJO 类中覆盖此方法。
If you override equals(Object) then you should also override hashcode()
如果你覆盖 equals(Object) 那么你也应该覆盖 hashcode()
Code snippet :
代码片段：
@Override
public String toString() {
return getName();
}
@Override
public boolean equals(Object obj) {
return !super.equals(obj);
}
@Override
public int hashCode() {
return getName().hashCode();
}
Edit :
编辑 ：
Moreover, The contains method is used for Object.So, your condition should look like this :
此外，包含方法用于对象。所以，你的情况应该是这样的：
(DataArrayList.secondArraylist.contains(actorList.get(position)))
Final code :
最终代码：
if (DataArrayList.secondArraylist.contains(actorList.get(position))) {
System.out.println("Data Exist(s)");
} else {
System.out.println("Not Exist(s)");
}
