存在父类Parent定义如下： public class Parent ｛public Object method(int a,int b) { return new Object（）；｝｝ 下面哪个方法能正确的重写Parent中的method方法

存在父类Parent定义如下：

public class Parent {
    public Object method(int a,int b) {
        return new Object();
    }
}

如果要正确重写`Parent`类中的`method`方法，需要满足以下条件：
1. 访问修饰符不能更严格，即不能用`private`或者其他访问权限更小的修饰符。
2. 返回值类型可以是原方法返回值类型的子类。
3. 方法名、参数列表、异常列表必须与原方法一致。
因此，下面的方法可以正确重写`Parent`类中的`method`方法：

public class Child extends Parent {
    @Override
    public String method(int a, int b) {
        return "child";
    }
}

其中`Child`类中的`method`方法的返回值类型是`String`，是`Object`的子类。同时，方法名、参数列表、异常列表也与`Parent`类中的`method`方法一致。

相关问题

public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) { // 使用LayoutInflater加载列表项的布局文件 View itemView = LayoutInflater.from(parent.getContext()) .inflate(R.layout.itemlayout2, parent, false); ImageView imageView1 = itemView.findViewById(R.id.sd_back); ImageView imageView2 = itemView.findViewById(R.id.sd_add); TextView textView=itemView.findViewById(R.id.sd_text); textView.setText(mVolumes.get(groupPosition)); imageView2.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Boolean isGroupExpanded = groupExpandState.get(groupPosition); groupExpandState.put(groupPosition, !isGroupExpanded); notifyDataSetChanged(); } }); imageView1.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent intent=new Intent(mContext, shedingActivity.class); intent.putExtra("key",groupPosition); mContext.startActivity(intent); } }); // 返回列表项的视图 return itemView; }报错java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object java.util.Map.get(java.lang.Object)' on a null object reference

这个错误提示中指出了空指针异常的原因，即在调用 `groupExpandState.get(groupPosition)` 方法时出现了空指针异常。根据代码，`groupExpandState` 变量应该是一个 `Map` 类型的实例，而在这里出现了空指针异常，说明它的值为 null。

因此，你需要在使用 `groupExpandState` 之前，先对其进行非空判断，以确保它不为空引用，例如：

imageView2.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        if (groupExpandState != null) {
            Boolean isGroupExpanded = groupExpandState.get(groupPosition);
            groupExpandState.put(groupPosition, !isGroupExpanded);
            notifyDataSetChanged();
        }
    }
});

你可以对 `imageView1` 的点击事件处理方法进行同样的修改。这样，就可以避免空指针异常了。

Implements method in Adapter in RecyclerView (androidx.recyclerview.widget)

To implement a custom Adapter in RecyclerView, you need to follow these steps:

1. Create a new class that extends RecyclerView.Adapter. This class will act as the adapter for your RecyclerView.

2. Override the onCreateViewHolder method, which is responsible for creating the ViewHolder objects for each item in the RecyclerView. In this method, you need to inflate the layout for the item and create a new ViewHolder object that holds a reference to the views in the layout.

3. Override the onBindViewHolder method, which is responsible for binding the data to the views in the ViewHolder object. In this method, you need to get the data for the current item and set it to the views in the ViewHolder object.

4. Override the getItemCount method, which returns the total number of items in the RecyclerView.

Here's an example code snippet for implementing a custom Adapter in RecyclerView:

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
    private List<String> mData;

    public MyAdapter(List<String> data) {
        mData = data;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.my_item_layout, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        String item = mData.get(position);
        holder.mTextView.setText(item);
    }

    @Override
    public int getItemCount() {
        return mData.size();
    }

    public static class ViewHolder extends RecyclerView.ViewHolder {
        public TextView mTextView;

        public ViewHolder(View itemView) {
            super(itemView);
            mTextView = itemView.findViewById(R.id.text_view);
        }
    }
}

In this example, the MyAdapter class extends RecyclerView.Adapter and takes a list of strings as data in its constructor. The onCreateViewHolder method inflates the layout for each item from a layout resource file and creates a new ViewHolder object. The onBindViewHolder method sets the text for each item in the RecyclerView. Finally, the getItemCount method returns the total number of items in the RecyclerView.

Note that in this example, the ViewHolder class is defined as a static inner class of the MyAdapter class. This is a common practice to keep the code organized and to avoid memory leaks.