android判断判断白天还是黑夜

package com.example.TimeTest;

import android.app.Activity;
import android.content.res.AssetManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.util.Log;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.IOException;
import java.io.InputStream;
import java.text.SimpleDateFormat;
import java.util.Date;

public class MyActivity extends Activity {
    /**
     * Called when the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        if (getCurrentTime()){

            Toast.makeText(this,"晚上",Toast.LENGTH_SHORT).show();
        }else {
            Toast.makeText(this,"白天",Toast.LENGTH_SHORT).show();
        }
        ImageView  imageView = (ImageView) findViewById(R.id.imageView)  ;
        imageView.setImageBitmap(getImageFromAssetsFile("d00.png"));
    }

    public boolean getCurrentTime(){
        SimpleDateFormat sdf = new SimpleDateFormat("HH");
        String hour= sdf.format(new Date());
        int k  = Integer.parseInt(hour)  ;
        if ((k>=0 && k<6) ||(k >=18 && k<24)){
          return true;
        } else {
            return false;
        }
    }

    private Bitmap getImageFromAssetsFile(String fileName)
    {
        Bitmap image = null;
        AssetManager am = getResources().getAssets();
        try
        {
            InputStream is = am.open("dd/"+fileName);
            image = BitmapFactory.decodeStream(is);
            is.close();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }

        return image;

    }
}