When searching for Java documentation the first search results will redirect you to the Java Platform SE 7 documentation.
This userscript will automatically redirect you to the Java Platform SE 8 documentation 

// ==UserScript==
// @name        JDK 8 docs
// @namespace   at.yawk.jdk8docs
// @include     https://docs.oracle.com/javase/*
// @version     1
// @grant       none
// ==/UserScript==

var pattern = /^(https?:\/\/docs\.oracle\.com\/javase\/)(?:7|6|1\.5\.0)(\/.*)$/i;
var result = pattern.exec(window.location.href);
if (result) {
  window.location = result[1] + "8" + result[2];
}

Thanks Yawkat for the userscript.