java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.pets/com.example.android.pets.CatalogActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'int android.database.Cursor.getCount()' on a null object reference

CatalogActivity

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.example.android.pets;

import android.content.ContentValues;
import android.content.Intent;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;

import static com.example.android.pets.data.PetContract.PetEntry.COLUMN_PET_BREED;
import static com.example.android.pets.data.PetContract.PetEntry.COLUMN_PET_GENDER;
import static com.example.android.pets.data.PetContract.PetEntry.COLUMN_PET_NAME;
import static com.example.android.pets.data.PetContract.PetEntry.COLUMN_PET_WEIGHT;
import static com.example.android.pets.data.PetContract.PetEntry.CONTENT_URI;
import static com.example.android.pets.data.PetContract.PetEntry.GENDER_MALE;
import static com.example.android.pets.data.PetContract.PetEntry._ID;

/**
 * Displays list of pets that were entered and stored in the app.
 */
public class CatalogActivity extends AppCompatActivity {

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

        // Setup FAB to open EditorActivity
        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(CatalogActivity.this, EditorActivity.class);
                startActivity(intent);
            }
        });
    }

    @Override
    protected void onStart() {
        super.onStart();
        displayDatabaseInfo();
    }

    /**
     * Temporary helper method to display information in the onscreen TextView about the state of
     * the pets database.
     */

    private void displayDatabaseInfo() {
        // Define a projection that specifies which columns from the database
        // you will actually use after this query.
        String[] projection = {_ID,
                                COLUMN_PET_NAME,
                                COLUMN_PET_BREED,
                                COLUMN_PET_GENDER,
                                COLUMN_PET_WEIGHT};

        // Perform a query on the provider using the ContentResolver.
        // Use the {"link PetEntry#CONTENT_URI} to access the pet data.
        Cursor cursor = getContentResolver().query(CONTENT_URI, // The content URI of the words table
                                                    projection, // The content URI with the words fill
                                                    null, // Selection criteria
                                                    null,   // Selection criteria
                                                     null); // The sort order for the returned rows.

        TextView displayView = (TextView) findViewById(R.id.text_view_pet);
        try {
            // Create a header in the Text View that looks like this:
            //
            // The pets table contains <number of rows in Cursor> pets
            // _id - name - breed - gender - weight
            //
            // IN the while loop below, iterate through the rows of the cursor and display the information
            // from each column in this order
            displayView.setText("The pets table contains " + cursor.getCount() + " pets.\n\n");
            displayView.append(_ID + " - " +
                    COLUMN_PET_NAME + " - " +
                    COLUMN_PET_BREED + " - " +
                    COLUMN_PET_GENDER + " - " +
                    COLUMN_PET_WEIGHT + "\n");

            // Figure out the index of each column
            int idColumnIndex = cursor.getColumnIndex(_ID);
            int nameColumnIndex = cursor.getColumnIndex(COLUMN_PET_NAME);
            int breedColumnIndex = cursor.getColumnIndex(COLUMN_PET_BREED);
            int genderColumnIndex = cursor.getColumnIndex(COLUMN_PET_GENDER);
            int weightColumnIndex = cursor.getColumnIndex(COLUMN_PET_WEIGHT);

            // Iterate through all the returned rows in the cursor.
            while (cursor.moveToNext()) {
                //Use that index to extract the String or int value of the word
                // at the current row the cursor is on.
                int currentID = cursor.getInt(idColumnIndex);
                String currentName = cursor.getString(nameColumnIndex);
                String currentBreed = cursor.getString(breedColumnIndex);
                int currentGender = cursor.getInt(genderColumnIndex);
                int currentWeight = cursor.getInt(weightColumnIndex);
                //Display the values from each column of the current row in the cursor in the TextView
                displayView.append(("\n" + currentID + " - " +
                        currentName + " - " +
                        currentBreed + " - " +
                        currentGender + " - " +
                        currentWeight));
            }
        } finally {
            // Always close the cursor when you're done reading from it. This releases all its
            // resources and makes it invalid.
            cursor.close();
        }
    }

    private void insertPet() {

        ContentValues values = new ContentValues();
        values.put(COLUMN_PET_NAME, "Toto");
        values.put(COLUMN_PET_BREED, "Terrier");
        values.put(COLUMN_PET_GENDER, GENDER_MALE);
        values.put(COLUMN_PET_WEIGHT, 7);

        Uri newUri = getContentResolver().insert(CONTENT_URI, values);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu options from the res/menu/menu_catalog.xml file.
        // This adds menu items to the app bar.
        getMenuInflater().inflate(R.menu.menu_catalog, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // User clicked on a menu option in the app bar overflow menu
        switch (item.getItemId()) {
            // Respond to a click on the "Insert dummy data" menu option
            case R.id.action_insert_dummy_data:
                insertPet();
                displayDatabaseInfo();
                return true;
            // Respond to a click on the "Delete all entries" menu option
            case R.id.action_delete_all_entries:
                // Do nothing for now
                return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

How can u use content provider without contract class . I think you need to define it .