using package manager to launch an installed app on button press

LauncherActivity.java

package spencerstudios.com.project1000_fx;

import android.content.ActivityNotFoundException;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;

public class LauncherActivity extends AppCompatActivity {

    private Button btn;
    private int index = 0;

    //populate this array with your package names....
    private final String[] packages = {"com.facebook.katana", "com.facebook,orca"};

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

        btn = (Button) findViewById(R.id.open_app_buttom);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                
                //lets pretend this is inside your onMenuSelected...
                Intent intent = getPackageManager().getLaunchIntentForPackage(packages[index]);
                startActivity(intent);

            }
        });
    }
}

It is helped me!!. Thank you so much TheSevenSeasOfBinary