Q:

htmlunit, change of address in the same window

    HtmlPage open1 =  (HtmlPage) webClient.getPage("http://www.google.com");

    ScriptResult result = open1.executeJavaScript("window.location.assign('https://www.google.com.tr/search?q'));

    HtmlPage afterExecution = (HtmlPage) result.getNewPage();

    System.out.println(afterExecution); //in window new adres

How do I open a new site in the same window?

A:

just call webClient.getPage("https://www.google.com.tr/search?q");. You don't need to call any javascript.
From the javadocs:

Convenient method to build an URL and load it into the current
  WebWindow as it would be done by getPage(WebWindow, WebRequest).

