本家の Android SDK が JDK7 までしか公式対応していないからな
多分JDK8でも問題ないはずだが･･･

http://developer.android.com/intl/ja/sdk/index.html

System Requirements
Windows
MicrosoftR WindowsR 8/7/Vista/2003 (32 or 64-bit)
2 GB RAM minimum, 4 GB RAM recommended
400 MB hard disk space
At least 1 GB for Android SDK, emulator system images, and caches
1280 x 800 minimum screen resolution
Java Development Kit (JDK) 7
Optional for accelerated emulator: IntelR processor with support for IntelR VT-x, IntelR EM64T (IntelR 64), and Execute Disable (XD) Bit functionality