用Android stdio写一个系统通知服务程序，一个按钮发送通知，一个按钮取消通知；写出Java代码和xml代码，和权限代码，及具体步骤

好的，下面是实现系统通知服务程序的Java代码和xml代码，以及相应的权限代码和具体步骤：

Java代码：

package com.example.notificationdemo;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.NotificationCompat;
import androidx.core.app.NotificationManagerCompat;

import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.os.Build;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private static final String CHANNEL_ID = "channel_id";
    private static final int NOTIFICATION_ID = 1;

    private Button mBtnSendNotification;
    private Button mBtnCancelNotification;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        createNotificationChannel();

        mBtnSendNotification = findViewById(R.id.btn_send_notification);
        mBtnCancelNotification = findViewById(R.id.btn_cancel_notification);

        mBtnSendNotification.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                sendNotification();
            }
        });

        mBtnCancelNotification.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                cancelNotification();
            }
        });
    }

    private void createNotificationChannel() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            CharSequence name = getString(R.string.channel_name);
            String description = getString(R.string.channel_description);
            int importance = NotificationManager.IMPORTANCE_DEFAULT;
            NotificationChannel channel = new NotificationChannel(CHANNEL_ID, name, importance);
            channel.setDescription(description);
            NotificationManager notificationManager = getSystemService(NotificationManager.class);
            notificationManager.createNotificationChannel(channel);
        }
    }

    private void sendNotification() {
        NotificationCompat.Builder builder = new NotificationCompat.Builder(this, CHANNEL_ID)
                .setSmallIcon(R.drawable.ic_notification)
                .setContentTitle(getString(R.string.notification_title))
                .setContentText(getString(R.string.notification_text))
                .setPriority(NotificationCompat.PRIORITY_DEFAULT);

        NotificationManagerCompat notificationManager = NotificationManagerCompat.from(this);
        notificationManager.notify(NOTIFICATION_ID, builder.build());
    }

    private void cancelNotification() {
        NotificationManagerCompat notificationManager = NotificationManagerCompat.from(this);
        notificationManager.cancel(NOTIFICATION_ID);
    }
}

xml代码：

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp">

    <Button
        android:id="@+id/btn_send_notification"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/btn_send_notification"/>

    <Button
        android:id="@+id/btn_cancel_notification"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/btn_cancel_notification"/>

</LinearLayout>

权限代码：

<uses-permission android:name="android.permission.VIBRATE" />
<uses-permission android:name="android.permission.FOREGROUND_SERVICE" />

具体步骤：

1. 在Android Studio中创建一个新的项目
2. 在res/values/strings.xml文件中添加以下内容：

<string name="channel_name">My Notification Channel</string>
<string name="channel_description">My Notification Channel Description</string>
<string name="notification_title">My Notification Title</string>
<string name="notification_text">My Notification Text</string>
<string name="btn_send_notification">Send Notification</string>
<string name="btn_cancel_notification">Cancel Notification</string>

3. 在res/drawable文件夹中添加一个名为ic_notification.png的图标作为通知的小图标
4. 在AndroidManifest.xml文件中添加以下内容：

<uses-permission android:name="android.permission.VIBRATE" />
<uses-permission android:name="android.permission.FOREGROUND_SERVICE" />

5. 在res/layout文件夹中创建一个名为activity_main.xml的布局文件，并添加以下内容：

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp">

    <Button
        android:id="@+id/btn_send_notification"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/btn_send_notification"/>

    <Button
        android:id="@+id/btn_cancel_notification"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/btn_cancel_notification"/>

</LinearLayout>

6. 在MainActivity.java文件中添加上述Java代码
7. 运行程序，点击“Send Notification”按钮发送通知，点击“Cancel Notification”按钮取消通知