public class MainActivity extends Activity {
  private WebView webview;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    webview = (WebView) findViewById(R.id.webview);
    //设置WebView属性，能够执行Javascript脚本
    WebSettings webSettings= webview.getSettings(); // webView: 类WebView的实例
    webSettings.setJavaScriptEnabled(true);
    webSettings.setSupportZoom(true);
    //设置默认缩放方式尺寸是far
    webSettings.setDefaultZoom(WebSettings.ZoomDensity.FAR);
    //设置出现缩放工具
    webSettings.setBuiltInZoomControls(true);
    webSettings .setLayoutAlgorithm(LayoutAlgorithm.SINGLE_COLUMN);
    //加载需要显示的网页
    webview.loadUrl("https://www.jb51.net/");
    //设置Web视图
    webview.setWebViewClient(new HelloWebViewClient ());
  }
  @Override
  //设置回退
  //覆盖Activity类的onKeyDown(int keyCoder,KeyEvent event)方法
  public boolean onKeyDown(int keyCode, KeyEvent event) {
    if ((keyCode == KeyEvent.KEYCODE_BACK) && webview.canGoBack()) {
      webview.goBack(); //goBack()表示返回WebView的上一页面
      return true;
    }
    return false;
  }
  //Web视图
  private class HelloWebViewClient extends WebViewClient {
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
      view.loadUrl(url);
      return true;
    }
  }
}