Java 软件改变移动网络模式

我想为自动交换网络模式创建程序。我已经阅读了相同的主题，并且找到了部分代码，但我没有什么问题

Boolean success = (Boolean) setPreferredNetwork.invoke(mTelephonyManager,
                networkType);

在这部分代码中，我不知道如何定义“mTelephonyManager”，有人能帮我吗？下面是几乎完整的代码

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package com.example.a4genforce;
import * *

public class MainActivity extends Activity {

int networkType = 12; //LTE/WCDMA

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    setPreferredNetwork(networkType);
}

public Method getHiddenMethod(String methodName, Class fromClass, Class[] params) {
    Method method = null;
    try {
        Class clazz = Class.forName(fromClass.getName());
        method = clazz.getMethod(methodName, params);
        method.setAccessible(true);
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (NoSuchMethodException e) {
        e.printStackTrace();
    }
    return method;
}

public void setPreferredNetwork(int networkType) {
    try {
        Method setPreferredNetwork = getHiddenMethod("setPreferredNetworkType",
                TelephonyManager.class, new Class[]{int.class});
        Boolean success = (Boolean) setPreferredNetwork.invoke(mTelephonyManager,
                networkType);
        Log.i(TAG, "Could set Network Type ::: " + (success.booleanValue() ? "YES" : "NO"));
    } catch (InvocationTargetException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    }
}

public void onMyClick(View view) {
    Toast.makeText(this, "Зачем вы нажали?", Toast.LENGTH_SHORT).show();
    try {
        Intent intent = new Intent("android.intent.action.MAIN");
        intent.setClassName("com.android.settings", "com.android.settings.RadioInfo");
        startActivity(intent);
    } catch (Exception e) {
        Toast.makeText(getApplicationContext(), " Device not supported", Toast.LENGTH_LONG).show();
    }
}
}

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
package="com.example.a4genforce">
<uses-permission android:name="android.permission.MODIFY_PHONE_STATE" tools:ignore="ProtectedPermissions"/>
<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"
    tools:ignore="GoogleAppIndexingWarning">

    <activity android:name=".MainActivity" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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