比较数组列表中的字符？

Question

我试图用自定义适配器填充RecycraView。此适配器接受具有setters和getters的模型。此模型包含三个参数：String username、int proPic和int bckgImg。我试图实现的是一个回收站视图与字母排序列表。我使用以下代码填充模型：

private ArrayList<FriendsModel> friendsData = new ArrayList<>(0);
friendsData.add(new FriendModel("Erick", R.drawable.default_pro_pic, R.drawable bckgImg);

填充完FriendModel的5个对象后，我继续比较ArrayList中的字符：

for(char alph = 'A'; alph <= 'Z'; alph++){
List<String> friends = getFriends(alph);

if(friends.size() > 0){
//Populate the Sorted Alphabetical view
}
 }

private List<String> getFriends(char alph) {
//Empty List used to populate when comparing existing model to alphabet
List<String> friends = new ArrayList<>();

//5 objects of FriendsData with three parameters
for (int i = 0; i < friendsData.size(); i++){
//If the first string parameter character at position 0 is equal to alph
 if(friendsData.get(i).toString().charAt(0) == alph){
 friends.add(friendsData.get(i).toString());
}
 }

return friends;
}

我不确定如果我这样做是正确的，什么是适当的或正确的方法来比较基于其模型的ArrayList中的字符？

Answer 1

使用模型对列表进行排序的正确方法是定义比较器。对于当前的示例，您使用了use。

Collections.sort(friendsData, new Comparator<FriendsModel>() {
@Override
public int compare(FriendsModel obj1, FriendsModel obj2) {
    return obj1.getUsername.compareTo(obj2.getUsername); //For Ascending order
//OR
    return obj2.getUsername.compareTo(obj1.getUsername); //For Descending order
  }
});

“compare”函数比较其两个参数的顺序。返回负整数、零或正整数，因为第一个参数小于、等于或大于第二个参数。

Answer 2

自定义比较器应该有所帮助

Collections.sort(list, new Comparator<String>() {
    @Override
    public int compare(String s1, String s2) {
        return s1.compareToIgnoreCase(s2);
    }
});

或者如果它不起作用，那就让我们来吧

Collections.sort(list, String.CASE_INSENSITIVE_ORDER);

Answer 3

不要使用构造函数来初始化变量，总是使用setter方法，这样的类也被称为pojo（普通的旧java对象）或VO（值对象）。

假设您的FriendModel类如下所示。。

public class FriendModel{
    String username;
    int proPic;
    int bckgImg;

    public FriendModel(){}

    //redundant constructor, you can remove this since you are using setter methods now.
    public FriendModel(String username, int proPic, int bckgImg){
        this.username=username;
        this.proPic=proPic;
        this.bckgImg=bckgImg;
    }

    //you'll need the below getters and setters..
    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public int getProPic() {
        return proPic;
    }

    public void setProPic(int proPic) {
        this.proPic = proPic;
    }

    public int getBckgImg() {
        return bckgImg;
    }

    public void setBckgImg(int bckgImg) {
        this.bckgImg = bckgImg;
    }

}

无论你在哪里做以下事情，

for(char alph = 'A'; alph <= 'Z'; alph++){
List<String> friends = getFriends(alph);

if(friends.size() > 0){
//Populate the Sorted Alphabetical view
}
 }

private List<String> getFriends(char alph) {
//Empty List used to populate when comparing existing model to alphabet
List<String> friends = new ArrayList<>();

//5 objects of FriendsData with three parameters
for (int i = 0; i < friendsData.size(); i++){
//If the first string parameter character at position 0 is equal to alph
 String username=friendsData.get(i).getUsername();      //get the username
 if(username.charAt(0) == alph){                        //compare the username with charater in alph variable
 friends.add(username);                                 //add in another list
}
 }

return friends;
}