Newbie, I encountered a problem at the beginning of learning Service
I did it according to the tutorial, and it crashed when starting the service
MyService.java

package com.example.administrator.myhhhhh;

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.util.Log;

public class MyService extends Service {

public MyService() {
}

@Override
public void onCreate() {
    Log.i("LOG","onCreat");
    super.onCreate();
}

@Override
public IBinder onBind(Intent intent) {
    // TODO: Return the communication channel to the service.
    throw new UnsupportedOperationException("Not yet implemented");
}

}

MainActivity.java

package com.example.administrator.myhhhhh;

import android.content.Intent;
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 Button start,stop;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button start=(Button)findViewById(R.id.button);
    Button stop=(Button)findViewById(R.id.button2);
    start.setOnClickListener(this);
    stop.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    Intent intent=new Intent("MyService");
    switch (v.getId()){
        case R.id.button:
            startService(intent);
            break;
        case R.id.button2:
            stopService(intent);
            break;
    }
}

}

Manifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk /res/android"

package="com.example.administrator.myhhhhh">

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <service
        android:name=".MyService"
        >
        <intent-filter>
            <action android:name="MyService"/>
        </intent-filter>
    </service>
</application>

</manifest>

Logcat error message:
05-04 21:28:44.377 21214-21214/com.example.administrator.myhhhhh E/AndroidRuntime: FATAL EXCEPTION: main

                                                                               Process: com.example.administrator.myhhhhh, PID: 21214
                                                                               java.lang.IllegalArgumentException: Service Intent must be explicit: Intent { act=MyService }
                                                                                   at android.app.ContextImpl.validateServiceIntent(ContextImpl.java:1851)
                                                                                   at android.app.ContextImpl.startServiceCommon(ContextImpl.java:1880)
                                                                                   at android.app.ContextImpl.startService(ContextImpl.java:1864)
                                                                                   at android.content.ContextWrapper.startService(ContextWrapper.java:516)
                                                                                   at com.example.administrator.myhhhhh.MainActivity.onClick(MainActivity.java:26)
                                                                                   at android.view.View.performClick(View.java:4918)
                                                                                   at android.view.View$PerformClick.run(View.java:20399)
                                                                                   at android.os.Handler.handleCallback(Handler.java:815)
                                                                                   at android.os.Handler.dispatchMessage(Handler.java:104)
                                                                                   at android.os.Looper.loop(Looper.java:194)
                                                                                   at android.app.ActivityThread.main(ActivityThread.java:5871)
                                                                                   at java.lang.reflect.Method.invoke(Native Method)
                                                                                   at java.lang.reflect.Method.invoke(Method.java:372)
                                                                                   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1119)
                                                                                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:885)

05-04 21:28:44.434 21214-21214/com.example.administrator.myhhhhh I/Process: Sending signal. PID: 21214 SIG: 9