Step1: permission needed to read contacts

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

Step2: ContentResolver provides access to the content provider. Its main work is to read the user's query and redirecting them to the appropriate provider. Here we are using Contentresolver object to get phone contents and Cursor used to get next data in your phone contents.

ContentResolver contentResolver = this.getContentResolver();
Cursor phones = contentResolver.query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI, null, null, null, ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME + " ASC");

// we perform loading contacts in background        
LoadContact loadContact = new LoadContact();
loadContact.execute();

Step3: Load data in background, we will perform long running operation in background like getting contact details and adding them to the data class. Now in onPostExecute() method we attach adapter and showing its values into the list.

class LoadContact extends AsyncTask<Void, Void, Void> {

        @Override
        protected Void doInBackground(Void... voids) {
            
	    // Get Contact list from Phone
            if (phones != null) {

                while (phones.moveToNext()) {

                    String name = phones.getString(phones.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
                    String phoneNumber = phones.getString(phones.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER)).replaceAll(" ", "");

		    // data class to save name and contact number
                    MobileContacts selectUser = new MobileContacts();
                    selectUser.setName(name);
                    selectUser.setPhone(phoneNumber);
                }
            } else {
                Toast.makeText(MobileContactsActivity.this, "No contacts in your contact list.", Toast.LENGTH_LONG).show();
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            super.onPostExecute(aVoid);

	    // now in the adapter class we only have to set name and phone number to the list
            adapter = new ContactsAdapter(selectUsers, MobileContactsActivity.this);
	    // adding adapter to the listview
            listView.setAdapter(adapter);
        }
    }