Webview Geri Tuşu

package com.example.ramazan.myapplication;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.webkit.WebView;
import android.webkit.WebViewClient;


public class MainActivity extends Activity {
    @SuppressLint("SetJavaScriptEnabled")
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        WebView myWebView = (WebView) findViewById(R.id.web_engine);
        myWebView.setWebViewClient(new MyBrowser());
        myWebView.clearCache(true);
        myWebView.clearHistory();
        myWebView.getSettings().setJavaScriptEnabled(true);
        myWebView.getSettings().setLoadsImagesAutomatically(true);
        myWebView.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY);
        myWebView.loadUrl("http://www.ruyatabirleriara.com/");
    }
    @Override
   

    private class MyBrowser extends WebViewClient {

        @Override
        public void onPageFinished(WebView view, String url) {
            if (findViewById(R.id.splach_screen).getVisibility() == View.VISIBLE) {
                // show webview
                findViewById(R.id.main_view).setVisibility(View.VISIBLE);
                // hide splash screen
                findViewById(R.id.splach_screen).setVisibility(View.GONE);
            }
        }
    }


}

    boolean doubleBackToExitPressedOnce = false;

    @Override
    public void onBackPressed() {
        if(webView.canGoBack())
        {
            webView.goBack();
        }
        else
        {
            if (doubleBackToExitPressedOnce) {
                super.onBackPressed();
                return;
            }

            this.doubleBackToExitPressedOnce = true;
            Toast.makeText(this, "Çıkmak için Geri'ye bir kere daha basınız.", Toast.LENGTH_SHORT).show();

            new Handler().postDelayed(new Runnable() {

                @Override
                public void run() {
                    doubleBackToExitPressedOnce=false;
                }
            }, 2000);
        }
    }

    boolean doubleBackToExitPressedOnce = false;

    @Override
    public void onBackPressed() {
        if(webView.canGoBack())
        {
            webView.goBack();
        }
        else
        {
            if (doubleBackToExitPressedOnce) {
                super.onBackPressed();
                return;
            }

            this.doubleBackToExitPressedOnce = true;
            Toast.makeText(this, "Çıkmak için Geri'ye bir kere daha basınız.", Toast.LENGTH_SHORT).show();

            new Handler().postDelayed(new Runnable() {

                @Override
                public void run() {
                    doubleBackToExitPressedOnce=false;
                }
            }, 2000);
        }
    }

C:\Users\Ramazan\AndroidStudioProjects\MyApplication4\app\src\main\java\com\example\ramazan\myapplication\MainActivity.java
Error:(30, 19) error: non-static method canGoBack() cannot be referenced from a static context
Error:(32, 20) error: non-static method goBack() cannot be referenced from a static context
Error:Execution failed for task ':app:compileDebugJavaWithJavac'.
> Compilation failed; see the compiler error output for details.
Information:Total time: 24.179 secs
Information:3 errors
Information:0 warnings
Information:See complete output in console