Read speed of SharedPreferences

According to this link, getSharedPreferences is not that much heavy because it opens file only when you call getSharedPreferences first time:

// There are 1000 String values in preferences

SharedPreferences first = context.getSharedPreferences("com.example.app", Context.MODE_PRIVATE);
// call time = 4 milliseconds

SharedPreferences second = context.getSharedPreferences("com.example.app", Context.MODE_PRIVATE);
// call time = 0 milliseconds

SharedPreferences third = context.getSharedPreferences("com.example.app", Context.MODE_PRIVATE);
// call time = 0 milliseconds

But using get methods will take some time for the first time you call it:

first.getString("key", null)
// call time = 147 milliseconds

first.getString("key", null)
// call time = 0 milliseconds

second.getString("key", null)
// call time = 0 milliseconds

third.getString("key", null)
// call time = 0 milliseconds 

Is there a way to put them in memory for reading?

They are in memory, after the first reference. The first time you retrieve a specific SharedPreferences (e.g., PreferenceManager.getDefaultSharedPreferences()), the data is loaded from disk, and kept around.

My advice is to test your performance first, and then start worrying about speed. In general, you'll be happier with an app that prioritizes maintainability as well as speed. When engineers start out to achieve performance before they get the app stable, the result is an app that runs a bit faster but has lots of bugs.