@Override public String toString() { return "Article{" + "id=" + id + ", title='" + title + '\'' + ", content='" + content + '\'' + ", created=" + created + ", modified=" + modified + ", categories='" + categories + '\'' + ", tags='" + tags + '\'' + ", hits=" + hits + ", allowComment=" + allowComment + ", commentsNum=" + commentsNum + ", thumbnail='" + thumbnail + '\'' + '}'; }分析这段代码的作用
时间: 2024-04-02 08:34:28 浏览: 13
这段代码是一个Java类Article的toString()方法的实现。它的作用是将Article对象的属性转换为一个字符串表示,方便输出和调试。具体来说,它输出了类的各个属性,包括id、title、content、created、modified、categories、tags、hits、allowComment、commentsNum和thumbnail,并将它们以特定的格式组织起来,用于输出或者日志记录等目的。这样,在需要输出Article对象的时候,只需要调用该对象的toString()方法,就可以得到一个包含所有属性的字符串。
相关问题
java参数校验校验集合
在Java中,如果想要对集合进行参数校验,可以使用自定义的集合类来包装集合,并在该包装类上添加@Valid注解。例如,可以创建一个自定义的List集合类来接收参数,并在该类上添加@Valid注解来进行参数校验。具体做法如下:
```java
public class StudentList<E> implements List<E> {
@Delegate
@Valid
public List<E> list = new ArrayList<>();
@Override
public String toString() {
return list.toString();
}
}
```
此外,还需要定义一个约束校验器,实现ConstraintValidator接口,并在该校验器中实现集合参数的校验逻辑。例如,可以创建一个ListValueConstraintValidator类来实现校验逻辑。具体做法如下:
```java
public class ListValueConstraintValidator implements ConstraintValidator<ListValue, Integer> {
private Set<Integer> set = new HashSet<>();
@Override
public void initialize(ListValue constraintAnnotation) {
int[] values = constraintAnnotation.values();
for (int val : values) {
set.add(val);
}
}
@Override
public boolean isValid(Integer value, ConstraintValidatorContext context) {
return set.contains(value);
}
}
```
以上就是在Java中对集合进行参数校验的方法。通过自定义集合类和约束校验器,可以实现对集合中每一项的参数校验。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
#### 引用[.reference_title]
- *1* *2* *3* [java注解校验参数](https://blog.csdn.net/zqy123456_123/article/details/127109216)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v92^chatsearchT3_1"}}] [.reference_item style="max-width: 100%"]
[ .reference_list ]
用Android编写新闻列表
编写新闻列表的过程大致如下:
1. 定义数据模型:首先需要定义一个News类,包含新闻的标题、内容、发布时间等信息。
2. 获取数据:从网络或本地数据库中获取新闻数据。网络数据可以使用Android自带的HttpURLConnection或第三方库如OkHttp进行请求,本地数据库可以使用SQLite。
3. 创建列表视图:使用Android提供的RecyclerView控件来展示新闻列表,并创建一个ViewHolder来显示每个新闻项的视图。
4. 绑定数据:将数据绑定到ViewHolder中,更新新闻项的视图。
5. 实现点击事件:为每个新闻项添加点击事件,跳转到新闻详情页。
具体实现过程如下:
1. 定义News类
```java
public class News {
private String title;
private String content;
private String time;
public News(String title, String content, String time) {
this.title = title;
this.content = content;
this.time = time;
}
public String getTitle() {
return title;
}
public String getContent() {
return content;
}
public String getTime() {
return time;
}
}
```
2. 获取数据
网络请求:
```java
public class NewsApi {
private static final String TAG = "NewsApi";
private static final String BASE_URL = "https://newsapi.org/v2/";
private static final String API_KEY = "YOUR_API_KEY";
public static List<News> getNews() throws IOException, JSONException {
String urlString = BASE_URL + "top-headlines?country=us&apiKey=" + API_KEY;
URL url = new URL(urlString);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.connect();
InputStream inputStream = connection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
StringBuffer stringBuffer = new StringBuffer();
String line;
while ((line = bufferedReader.readLine()) != null) {
stringBuffer.append(line);
}
String responseString = stringBuffer.toString();
JSONObject responseJson = new JSONObject(responseString);
JSONArray articles = responseJson.getJSONArray("articles");
List<News> newsList = new ArrayList<>();
for (int i = 0; i < articles.length(); i++) {
JSONObject article = articles.getJSONObject(i);
String title = article.getString("title");
String content = article.getString("description");
String time = article.getString("publishedAt");
News news = new News(title, content, time);
newsList.add(news);
}
return newsList;
}
}
```
本地数据库:
```java
public class NewsDbHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME = "news.db";
private static final int DATABASE_VERSION = 1;
private static final String SQL_CREATE_ENTRIES =
"CREATE TABLE " + NewsEntry.TABLE_NAME + " (" +
NewsEntry._ID + " INTEGER PRIMARY KEY," +
NewsEntry.COLUMN_NAME_TITLE + " TEXT," +
NewsEntry.COLUMN_NAME_CONTENT + " TEXT," +
NewsEntry.COLUMN_NAME_TIME + " TEXT)";
private static final String SQL_DELETE_ENTRIES =
"DROP TABLE IF EXISTS " + NewsEntry.TABLE_NAME;
public NewsDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public void onCreate(SQLiteDatabase db) {
db.execSQL(SQL_CREATE_ENTRIES);
}
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL(SQL_DELETE_ENTRIES);
onCreate(db);
}
public void addNews(News news) {
SQLiteDatabase db = getWritableDatabase();
ContentValues values = new ContentValues();
values.put(NewsEntry.COLUMN_NAME_TITLE, news.getTitle());
values.put(NewsEntry.COLUMN_NAME_CONTENT, news.getContent());
values.put(NewsEntry.COLUMN_NAME_TIME, news.getTime());
db.insert(NewsEntry.TABLE_NAME, null, values);
db.close();
}
public List<News> getNews() {
SQLiteDatabase db = getReadableDatabase();
String[] projection = {
NewsEntry._ID,
NewsEntry.COLUMN_NAME_TITLE,
NewsEntry.COLUMN_NAME_CONTENT,
NewsEntry.COLUMN_NAME_TIME
};
Cursor cursor = db.query(
NewsEntry.TABLE_NAME,
projection,
null,
null,
null,
null,
null
);
List<News> newsList = new ArrayList<>();
while (cursor.moveToNext()) {
String title = cursor.getString(cursor.getColumnIndexOrThrow(NewsEntry.COLUMN_NAME_TITLE));
String content = cursor.getString(cursor.getColumnIndexOrThrow(NewsEntry.COLUMN_NAME_CONTENT));
String time = cursor.getString(cursor.getColumnIndexOrThrow(NewsEntry.COLUMN_NAME_TIME));
News news = new News(title, content, time);
newsList.add(news);
}
cursor.close();
db.close();
return newsList;
}
public static class NewsEntry implements BaseColumns {
public static final String TABLE_NAME = "news";
public static final String COLUMN_NAME_TITLE = "title";
public static final String COLUMN_NAME_CONTENT = "content";
public static final String COLUMN_NAME_TIME = "time";
}
}
```
3. 创建列表视图
在布局文件中添加RecyclerView控件:
```xml
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="16dp"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
tools:listitem="@layout/item_news" />
```
在Activity中获取RecyclerView并设置Adapter:
```java
public class NewsListActivity extends AppCompatActivity {
private RecyclerView recyclerView;
private NewsAdapter newsAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_news_list);
recyclerView = findViewById(R.id.recycler_view);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
newsAdapter = new NewsAdapter(new ArrayList<>());
recyclerView.setAdapter(newsAdapter);
// 获取新闻数据并更新列表
List<News> newsList = getNews();
newsAdapter.updateNews(newsList);
}
private List<News> getNews() {
// 获取新闻数据
return null;
}
}
```
4. 绑定数据
创建ViewHolder来显示新闻项的视图:
```java
public class NewsViewHolder extends RecyclerView.ViewHolder {
private TextView titleTextView;
private TextView contentTextView;
private TextView timeTextView;
public NewsViewHolder(@NonNull View itemView) {
super(itemView);
titleTextView = itemView.findViewById(R.id.title_text_view);
contentTextView = itemView.findViewById(R.id.content_text_view);
timeTextView = itemView.findViewById(R.id.time_text_view);
}
public void bind(News news) {
titleTextView.setText(news.getTitle());
contentTextView.setText(news.getContent());
timeTextView.setText(news.getTime());
}
}
```
创建Adapter来管理新闻列表的视图:
```java
public class NewsAdapter extends RecyclerView.Adapter<NewsViewHolder> {
private List<News> newsList;
public NewsAdapter(List<News> newsList) {
this.newsList = newsList;
}
public void updateNews(List<News> newsList) {
this.newsList = newsList;
notifyDataSetChanged();
}
@NonNull
@Override
public NewsViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news, parent, false);
return new NewsViewHolder(itemView);
}
@Override
public void onBindViewHolder(@NonNull NewsViewHolder holder, int position) {
News news = newsList.get(position);
holder.bind(news);
}
@Override
public int getItemCount() {
return newsList.size();
}
}
```
5. 实现点击事件
在ViewHolder中为新闻项添加点击事件:
```java
public class NewsViewHolder extends RecyclerView.ViewHolder {
private TextView titleTextView;
private TextView contentTextView;
private TextView timeTextView;
public NewsViewHolder(@NonNull View itemView) {
super(itemView);
titleTextView = itemView.findViewById(R.id.title_text_view);
contentTextView = itemView.findViewById(R.id.content_text_view);
timeTextView = itemView.findViewById(R.id.time_text_view);
itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// 跳转到新闻详情页
}
});
}
public void bind(News news) {
titleTextView.setText(news.getTitle());
contentTextView.setText(news.getContent());
timeTextView.setText(news.getTime());
}
}
```
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