How to activate “Share” button in android app?

My code in MainActivity.java:

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 {
Button btn;
    @Override    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn= (Button)findViewById(R.id.button);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override            public void onClick(View view) {
                Intent shareIntent = new Intent(Intent.ACTION_SEND);
                shareIntent.setType("text/plain");
                shareIntent.putExtra(Intent.EXTRA_TEXT,"Text");
                shareIntent.putExtra(Intent.EXTRA_SUBJECT,"Subject");
                startActivity(Intent.createChooser(shareIntent,"Share Using"));
            }
        });

    }
}

Code in tab (xml) (If need):

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context=".MainActivity">


    <Button        android:id="@+id/button"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignParentBottom="true"        android:layout_centerHorizontal="true"        android:layout_marginBottom="215dp"        android:text="Share Button" />
</RelativeLayout>