Question

我在Android Studio中有一个名为MainActivity.java的主java文件：

public class MainActivity extends AppCompatActivity {

    private static final String TAG = MainActivity.class.getSimpleName();
    private RecyclerView recyclerView;
    private LinearLayoutManager linearLayoutManager;
    private RecyclerViewAdapter recyclerViewAdapter;
    private EditText addTaskBox;
    private DatabaseReference databaseReference;
    private List<Task> allTask;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        allTask = new ArrayList<>();
        databaseReference = FirebaseDatabase.getInstance().getReference();
        addTaskBox = (EditText)findViewById(R.id.add_task_box);
        recyclerView = (RecyclerView)findViewById(R.id.task_list);
        linearLayoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(linearLayoutManager);
        Button addTaskButton = (Button)findViewById(R.id.add_task_button);
        assert addTaskButton != null;
        addTaskButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String enteredTask = addTaskBox.getText().toString();
                if(TextUtils.isEmpty(enteredTask)){
                    Toast.makeText(MainActivity.this, "You must enter a task       first", Toast.LENGTH_LONG).show();
                    return;
                }
                if(enteredTask.length() < 6){
                    Toast.makeText(MainActivity.this, "Task count must be more than 6", Toast.LENGTH_LONG).show();
                    return;
                }else{
                    Task taskObject = new Task(enteredTask);
                    databaseReference.push().setValue(taskObject);
                    addTaskBox.setText("");
                }
            }
        });
        databaseReference.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                getAllTask(dataSnapshot);
            }
            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String s) {
                getAllTask(dataSnapshot);
            }
            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {
                taskDeletion(dataSnapshot);
            }
            @Override
            public void onChildMoved(DataSnapshot dataSnapshot, String s) {
            }
            @Override
            public void onCancelled(DatabaseError databaseError) {
            }
        });
    }
    private void getAllTask(DataSnapshot dataSnapshot){
        for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){
            String taskTitle = singleSnapshot.getValue(String.class);
            allTask.add(new Task(taskTitle));
            recyclerViewAdapter = new RecyclerViewAdapter(MainActivity.this, allTask);
            recyclerView.setAdapter(recyclerViewAdapter);
        }
    }
    private void taskDeletion(DataSnapshot dataSnapshot){
        for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()) {
            String taskTitle = singleSnapshot.getValue(String.class);
            for(int i = 0; i < allTask.size(); i++){
                if(allTask.get(i).getTask().equals(taskTitle)){
                    allTask.remove(i);
                }
            }
            Log.d(TAG, "Task tile " + taskTitle);
            recyclerViewAdapter.notifyDataSetChanged();
            recyclerViewAdapter = new RecyclerViewAdapter(MainActivity.this,    allTask);
            recyclerView.setAdapter(recyclerViewAdapter);
        }
    }
}

另一个名为Task.java的类：

public class Task {
    private String task;
    public Task() {}
    public Task(String task) {
        this.task = task;
    }
    public String getTask() {
        return task;
    }
}

我收到这些错误：

错误：（53,35）错误：任务是抽象的;无法实例化

错误：（82,25）错误：任务是抽象的;无法实例化

错误：（91,34）错误：找不到符号方法getTask（）

如果我正确使用类Task，为什么会这样？

我该怎么办？

Answer 1

在MainActivity.java的顶部，您已获得import语句，该语句导入的Task课程不是您撰写的课程。您需要删除import语句才能使用自己的类。如果你不这样做，那么当编译器在你的代码中看到Task时，它假定你指的是你导入的那个，而不是与MainActivity.java在同一个包中的那个。

我不能用一个类来主

1 个答案: