Piece of code ("onOptionsItemSelected" method) to share anything in a Android Activity

ActivityToShare.java

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();

    if (id == R.id.action_share) {
        Intent sendIntent = new Intent();
        sendIntent.setAction(Intent.ACTION_SEND);
        sendIntent.putExtra(Intent.EXTRA_TEXT, "TEXTO A SER COMPARTILHADO");
        sendIntent.setType("text/plain");
        startActivity(Intent.createChooser(sendIntent, "Compartilhe com..."));
        return true;
    }

    return super.onOptionsItemSelected(item);
}

Remember: you need a menu_layout.xml file like that:

<?xml version="1.0" encoding="utf-8"?>

<menu
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <item android:id="@+id/action_share"
        android:title="@string/action_share"
        android:icon="@drawable/ic_action_share"
        app:showAsAction="always" />

    <item android:id="@+id/action_about"
        android:icon="@drawable/ic_action_about"
        android:title="@string/action_about"
        android:orderInCategory="100"
        app:showAsAction="ifRoom" />
</menu>