NotificationUtils:

import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.content.Context;
import android.content.ContextWrapper;
import android.os.Build;
import android.support.v4.app.NotificationCompat;
 
/**
 * Created by Cjz on 2018/9/15.
 */
 
public class NotificationUtils extends ContextWrapper {
 
    private NotificationManager manager;
    public static final String id = "Notification_Channel";
    public static final String name = "Notification_Name";
 
    public NotificationUtils(Context context){
        super(context);
    }
 
    public void createNotificationChannel(){
        NotificationChannel channel = new NotificationChannel(id, name, NotificationManager.IMPORTANCE_HIGH);
        getManager().createNotificationChannel(channel);
    }
    private NotificationManager getManager(){
        if (manager == null){
            manager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
        }
        return manager;
    }
    public Notification.Builder getChannelNotification(String title, String content){
        return new Notification.Builder(getApplicationContext(), id)
                .setContentTitle(title)
                .setContentText(content)
                .setSmallIcon(android.R.drawable.stat_notify_more)
                .setAutoCancel(true);
    }
    public NotificationCompat.Builder getNotification_25(String title, String content){
        return new NotificationCompat.Builder(getApplicationContext())
                .setContentTitle(title)
                .setContentText(content)
                .setSmallIcon(android.R.drawable.stat_notify_more)
                .setAutoCancel(true);
    }
    public void sendNotification(String title, String content){
        if (Build.VERSION.SDK_INT>=26){
            createNotificationChannel();
            Notification notification = getChannelNotification
                    (title, content).build();
            getManager().notify(1,notification);
        }else{
            Notification notification = getNotification_25(title, content).build();
            getManager().notify(1,notification);
        }
    }
}
 

MainActivity:

import android.app.NotificationManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
 
public class MainActivity extends AppCompatActivity implements View.OnClickListener{
 
    private NotificationManager mManager;
    private Button mSend;
    private NotificationUtils notificationUtils;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mSend = findViewById(R.id.send_notification);
        mSend.setOnClickListener(this);
    }
 
    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.send_notice:
                NotificationUtils notificationUtils = new NotificationUtils(this);
                notificationUtils.sendNotification("This is content title", "This is                     
                     content text");
        }
    }
}
 

佈局檔案activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
 
    <Button
        android:id="@+id/send_notification"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Send Notification"/>
 
</LinearLayout>