How Do I Deal With The Null Point Exception In Android Studio

package com.example.dell.alc;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;


public class MainActivity extends ActionBarActivity {
    public static final String TAG =  "Lifecycle_activity";
    public static int createCount = 0;
    public static int startCount = 0;
    public static int restartCount = 0;
    public static int resumeCount = 0;
    public static int pauseCount = 0;
    public static int stopCount = 0;
    public static int destroyCount = 0;
    TextView tv,tv1,tv2,tv3,tv4,tv5,tv6;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        createCount++;
        Log.d(TAG,"The number of times the Activity created: " + createCount);
        if(createCount>=1){
            TextView tv = (TextView) findViewById(R.id.onCreate);
            tv.setText("Start count:" + createCount);
        }
        setContentView(R.layout.activity_main);
    }

    @Override
    protected void onStart() {
        super.onStart();
        startCount++;
        Log.d(TAG,"The number of times the Activity started: " + startCount);
        if(startCount>=1){
            TextView tv1 = (TextView) findViewById(R.id.onStart);
            tv1.setText("Start count:" + startCount);
        }
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        startCount++;
        Log.d(TAG,"The number of times the Activity Restarted: " + startCount);
        if(restartCount>1){
            TextView tv2 = (TextView) findViewById(R.id.onRestart);
            tv2.setText("Restart count:" + restartCount);
        }
    }

    @Override
    protected void onStop() {
        super.onStop();
        stopCount++;
        Log.d(TAG,"The number of times the Activity stopped: " + stopCount);
        if(stopCount>=1){
            tv3 = (TextView) findViewById(R.id.onStop);
            tv3.setText("stop count:" + stopCount);
        }
    }

    @Override
    protected void onResume() {
        super.onResume();
        resumeCount++;
        Log.d(TAG,"The number of times the Activity is resumed: " + resumeCount);
        if(resumeCount>=1){
            TextView tv4 = (TextView) findViewById(R.id.onResume);
            tv4.setText("Resume count:" + resumeCount);
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        startCount++;
        Log.d(TAG,"The number of times the Activity paused: " + pauseCount);
        if(pauseCount>=0){
            TextView tv5 = (TextView) findViewById(R.id.onPause);
            tv5.setText("pause count:" + pauseCount);
        }
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        destroyCount++;
        Log.d(TAG, "The number of times the Activity created: " + destroyCount);
        if (destroyCount >= 0) {
            TextView tv6 = (TextView) findViewById(R.id.onDestroy);
            tv6.setText("destroy count:" + destroyCount);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}