java - 如何在 Java 中反转数组

Question

这个问题已经有答案了:

Reversing an Array in Java [duplicate] (15 个回答)

已关闭 4 年前。

我有一个应用程序的源代码，它显示在后端服务器中上传的值列表，但问题是它以相反的顺序显示值(首先列出较早上传的内容)我希望它以相反的顺序排序(按日期)。

  public class SelectQuizActivity extends AppCompatActivity {

private static final String TAG = SelectQuizActivity.class.getSimpleName();

private int categoryId;
private String catName;
private String catImage;

private ImageView categoryImage;
private TextView categoryName;

private RecyclerView quizRecyclerView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_select_quiz);

    categoryId = getIntent().getExtras().getInt(Constants.CATEGORY);
    catName = getIntent().getExtras().getString(Constants.CATEGORY_NAME);
    catImage = getIntent().getExtras().getString(Constants.CATEGORY_IMAGE);

    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
    if(getSupportActionBar() != null){
        getSupportActionBar().setElevation(0);
    }
    setTitle("");

    categoryImage = (ImageView)findViewById(R.id.quiz_category_image);
    categoryName = (TextView)findViewById(R.id.quiz_category_name);

    quizRecyclerView = (RecyclerView)findViewById(R.id.quiz_category);
    quizRecyclerView.setLayoutManager(new GridLayoutManager(SelectQuizActivity.this, 3));
    quizRecyclerView.setHasFixedSize(true);

    if(Helper.isNetworkAvailable(this)){
        allSubcategoryInCategory(catName);
    }else{
        DisplayMessage.displayErrorMessage(this, "No network available");
    }

}

private void allSubcategoryInCategory(String name){
    Map params = getParams(name);
    GsonRequest<SingleQuizObject[]> serverRequest = new GsonRequest<SingleQuizObject[]>(
            Request.Method.POST,
            Constants.PATH_TO_QUIZ_SUBCATEGORIES,
            SingleQuizObject[].class,
            params,
            createRequestSuccessListener(),
            createRequestErrorListener());

    ((CustomApplication)getApplication()).getNetworkCall().callToRemoteServer(serverRequest);
}

private Map getParams(String name){
    Map<String, String> params = new HashMap<String,String>();
    params.put(Constants.NAME, name);
    return params;
}

private Response.Listener<SingleQuizObject[]> createRequestSuccessListener() {
    return new Response.Listener<SingleQuizObject[]>() {
        @Override
        public void onResponse(SingleQuizObject[] response) {
            try {
                if(response != null){
                    categoryName.setText(catName + " subcategories");
                    String serverImagePath = Constants.PUBLIC_FOLDER + catImage;
                    RequestOptions requestOptions = new RequestOptions();
                    requestOptions.diskCacheStrategy(DiskCacheStrategy.ALL);
                    Glide.with(SelectQuizActivity.this).load(serverImagePath).apply(requestOptions.fitCenter().override(80, 80)).into(categoryImage);
                    ArrayList<SingleQuizObject> list = arrayToListObject(response);
                    Collections.reverse(list);
                    CategoryAdapter mAdapter = new CategoryAdapter(SelectQuizActivity.this, arrayToListObject(list));
                    quizRecyclerView.setAdapter(mAdapter);
                } else{
                    displayErrorMessage(SelectQuizActivity.this, "No subcategory found ");
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    };
}

private Response.ErrorListener createRequestErrorListener() {
    return new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            error.printStackTrace();
        }
    };
}


private List<SingleQuizObject> arrayToListObject(SingleQuizObject[] response){
    List<SingleQuizObject> allCategories = new ArrayList<>();
    Collections.addAll(allCategories, response);
    return allCategories;
}

}

上面的代码从类别适配器获取输入并将其显示为回收器 View

Answer 1

按 Java Collection 类反向列表

Collections.reverse(arrayToListObject(response));

或反向RecyclerView项目。

LinearLayoutManager lm = new LinearLayoutManager(YourActivity.this);
lm.setReverseLayout(true);
lm.setStackFromEnd(true);

编辑示例

由于你没有做正确的事情，这就是方法

ArrayList<SingleQuizObject> list = arrayToListObject(response);
Collections.reverse(list);
CategoryAdapter mAdapter = new CategoryAdapter(SelectQuizActivity.this, list);

原因

您反转了列表的另一个副本，并插入了另一个列表。因此，首先保留列表，反转它，然后在适配器中插入相同的列表。