找不到类符号--Android Studio

Question

我刚刚开始按照本教程构建一个Android应用程序。 一切都很顺利，直到我们制作一个Intent对象来调出NoteSelect活动的最后一步，尽管该类在同一个文件夹中。 这是错误 -

Information:Gradle tasks [:app:assembleDebug]
F:\Path\Memos\app\src\main\java\com\example\memos\memos\MainActivity.java
Error:(99, 57) error: cannot find symbol class NoteSelect
Error:Execution failed for task ':app:compileDebugJavaWithJavac'.
> Compilation failed; see the compiler error output for details.
Information:BUILD FAILED in 19s
Information:2 errors
Information:0 warnings
Information:See complete output in console

这是层次结构 -

MainActivity.java （onOptionsItemSelected（））

package com.example.memos.memos;

@Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        Intent myIntent = new Intent(MainActivity.this, NoteSelect.class);
        if (id == R.id.action_settings) {
            startActivity(myIntent);
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

NoteSelect.java （未提及琐碎的导入）

import com.example.memos.memos.R;

public class NoteSelect extends AppCompatActivity {

    private List <NotesBuilder> notesList = new ArrayList<>();
    private NotesAdapter nAdapter;
    private RecyclerView notesRecycler;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_note_select);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        notesRecycler = findViewById(R.id.notes);

        nAdapter = new NotesAdapter(notesList);
        RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
        notesRecycler.setLayoutManager(mLayoutManager);
        notesRecycler.setItemAnimator(new DefaultItemAnimator());
        notesRecycler.setAdapter(nAdapter);

        prepareNotes();

    }

    private void prepareNotes() {
        File directory;
        directory = getFilesDir();
        File[] files = directory.listFiles();
        String theFile;
        for (int f = 1; f <= files.length; f++) {
            theFile = "Note" + f + ".txt";
            NotesBuilder note = new NotesBuilder(theFile, Open(theFile));
            notesList.add(note);
        }

    }

    public String Open(String fileName) {
        String content = "";
        try {
            InputStream in = openFileInput(fileName);
            if ( in != null) {
                InputStreamReader tmp = new InputStreamReader( in );
                BufferedReader reader = new BufferedReader(tmp);
                String str;
                StringBuilder buf = new StringBuilder();
                while ((str = reader.readLine()) != null) {
                    buf.append(str + "\n");
                } in .close();

                content = buf.toString();
            }
        } catch (java.io.FileNotFoundException e) {} catch (Throwable t) {
            Toast.makeText(this, "Exception: " + t.toString(), Toast.LENGTH_LONG).show();
        }

        return content;
    }
}

AndroidManifest.xml ， content_note_select.xml和activity_note_select.xml似乎存在问题。

到目前为止，我已尝试在与MainActivity.java相同的包中包含NoteSelect.java ，它解决了NoteSelect类未找到的问题，但进一步导致NoteBuilder和NoteAdapter类在NoteSelect.java中找不到问题。 此外，由于在原始教程中没有提到这样的内容，我不喜欢它。

我出错的任何想法？

Answer 1

到目前为止，我已经尝试在与MainActivity.java相同的包中包含NoteSelect.java，它解决了NoteSelect类没有找到问题，但进一步导致找不到NoteBuilder和NoteAdapter类

嗯，这是正确的，但你还需要移动其他类而不是将它们留在src/main/java文件夹中

Java无法解析当前包“之上”的类。

试试这个布局

com.example.memos/
    MainActivity.java
    notes/
        NoteSelectionActivity.java   <--- It's an activity, so rename your class to this
        NotesAdapter.java
        Note.java  <---- A POJO class. // There's no reason to name it "Builder" when it isn't using a "Builder Pattern"

然后在MainActivity中

package com.example.memos;

import com.example.memos.notes.NoteSelectionActivity;

并且在NoteSelectionActivity中

package com.example.memos.notes;

// No imports needed for classes in the same package