I found interesting things today, While reading Android API document, I found (View Source) link beside class name. Now It is very easy to quick look of class/source code from API document.
Let's check source code of Activity class.
Step 1: Open following link in your browser
Step 2: Click on View Source link beside Activity
If you don't see View Source link then install "Android SDK Reference Search" Chrome Extension
Step 1: Open following link
Step 2: Click "Add to chrome", after installation open following link to verify extension