In practical development, you may encounter other apk s packaged in your own application and installed together. Here are the steps:

First copy the test.apk to the main/assets directory and apply for read and write access to the memory card in the manifest file:

    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Additionally, mobile phones with 6.0 or more require dynamic permissions in the code:

if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED
    || ContextCompat.checkSelfPermission(this,Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {

            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE,
                    Manifest.permission.READ_EXTERNAL_STORAGE}, REQUEST_CODE);

@Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {

        // super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (requestCode == REQUEST_CODE) {
            if (grantResults[0] == PackageManager.PERMISSION_GRANTED && grantResults[1] == PackageManager.PERMISSION_GRANTED) {
                ...
            } else {
                finish();
            }
            return;
        }
    }

To be compatible with phones over 7.0, to use a provider, add a provider under the application node in the manifest file:

<manifest>
    ...
    <application>
        ...
        <provider
            android:name="android.support.v4.content.FileProvider"
            android:authorities="com.example.app.fileprovider" //Custom name To avoid duplication, the recommended setting is: Package name.fileprovider
            android:exported="false"
            android:grantUriPermissions="true">
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/provider_paths"
                />
        </provider>
        ...
    </application>
</manifest>

Then create a new XML folder in the res directory and a new provider_paths.xml file in the XML folder (corresponding to the resource in the provider):

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <!--"."Represents all paths-->
    <external-path name="external_files" path="."/>
	<!--Fill in your package name-->
    <external-path path="Android/data/com.example.app/" name="share_files_path" />
    <external-path path="." name="root_path" />
</paths>

ok, the preparation is complete, so let's officially start:

Copy test.apk from the assets directory to the memory card:

	/**
	 * Copy files to SD card
	 * @param context
	 * @param fileName Copied file name
	 * @param path  Saved directory path
	 * @return
	 */
	public static Uri copyAssetsFile(Context context, String fileName, String path) {
		try {
			InputStream mInputStream = context.getAssets().open(fileName);
			File file = new File(path);
			if (!file.exists()) {
				file.mkdir();
			}
			File mFile = new File(path + File.separator + "test.apk");
			if(!mFile.exists())
				mFile.createNewFile();
			LogUtil.e(TAG,"Start Copying");
			FileOutputStream mFileOutputStream = new FileOutputStream(mFile);
			byte[] mbyte = new byte[1024];
			int i = 0;
			while((i = mInputStream.read(mbyte)) > 0){
				mFileOutputStream.write(mbyte, 0, i);
			}
			mInputStream.close();
			mFileOutputStream.close();
			Uri uri = null;
			try{
				if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.N){
					//Package name.fileprovider
					uri = FileProvider.getUriForFile(context, "com.example.app.fileprovider", mFile);
				}else{
					uri = Uri.fromFile(mFile);
				}
			}catch (ActivityNotFoundException anfe){
				LogUtil.e(TAG,anfe.getMessage());
			}
			MediaScannerConnection.scanFile(context, new String[]{mFile.getAbsolutePath()}, null, null);
			LogUtil.e(TAG,"Copy complete:" + uri);
			return uri;
		} catch (IOException e) {
			e.printStackTrace();
			Log.e(TAG, fileName + "not exists" + "or write err");
			return null;
		} catch (Exception e) {
			return null;
		}
	}

Then install test.apk,

/**
	 * Install apk
	 * @param uri apk Stored Path
	 * @param context
	 */
	public static void openApk(Uri uri, Context context) {
		Intent intent = new Intent();
		intent.setAction(Intent.ACTION_VIEW);
		if (Build.VERSION.SDK_INT >= 24) {
			intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
			intent.setDataAndType(uri, "application/vnd.android.package-archive");
		} else {
			intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
		}
		intent.setDataAndType(uri, "application/vnd.android.package-archive");
		context.startActivity(intent);
	}

Finally, you can check to see if test.apk is installed:

/**
	 * App Is it installed
	 * @param mContext
	 * @param packageName Package Name
	 * @return
	 */
	private boolean isAppInstall(Context mContext, String packageName){
		PackageInfo mInfo;
		try {
			mInfo = mContext.getPackageManager().getPackageInfo(packageName, 0 );
		} catch (Exception e) {
			// TODO: handle exception
			mInfo = null;
			Log.i(TAG, "Installed package name not found");
		}
		if(mInfo == null){
			return false;
		}else {
			return true;
		}
	}