ブラウザ

package self.mybrowser;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Patterns;
import android.view.View;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    private WebView myWebView;
    private EditText urlText;

    private static final String INITIAL_WEBSITE = "http://finance.yahoo.co.jp";



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

        myWebView = (WebView) findViewById(R.id.myWebView);
        urlText = (EditText) findViewById(R.id.urlText);

        myWebView.getSettings().setJavaScriptEnabled(true);
        myWebView.setWebViewClient(new WebViewClient(){
            @Override
                    public void onPageFinished(WebView view, String url){
                getSupportActionBar().setSubtitle(view.getTitle());
                urlText.setText(url);
            }
        });
        myWebView.loadUrl(INITIAL_WEBSITE);
    }

    public void clearUrl(View view){
        urlText.setText("");
    }

    public void showWebSite(View view){
        String url = urlText.getText().toString().trim();

        if (!Patterns.WEB_URL.matcher(url).matches()){
            urlText.setError("Invalid URL");
        } else {
            if(url.startsWith("http;//") && !url.startsWith("https://")){
                url = "http://" + url;
            }
            myWebView.loadUrl(url);
        }
    }

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

    @Override
    protected void onDestroy(){
        super.onDestroy();
        if(myWebView != null){
            myWebView.stopLoading();
            myWebView.setWebViewClient(null);
            myWebView.destroy();
        }
        myWebView = null;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="self.mybrowserapp.MainActivity">

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <EditText
            android:layout_weight="1"
            android:id="@+id/urlText"
            android:layout_width="0dp"
            android:onClick="clearUrl"
            android:inputType="text|textNoSuggestions"
            android:layout_height="wrap_content"/>

        <Button
            android:text="Browse"
            android:onClick="showWebsite"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
    </LinearLayout>

    <WebView
        android:layout_weight="1"
        android:id="@+id/myWebView"
        android:layout_width="match_parent"
        android:layout_height="0dp"></WebView>

</LinearLayout>