[Q] You are attempting to build with an unsupported version of java.

blttalas@acer:~/android-sdk-linux/platform-tools$ make -j4 out/host/linux-x86/bin/unpackbootimg
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PLATFORM_VERSION_CODENAME=REL
PLATFORM_VERSION=4.1.2
TARGET_PRODUCT=full
TARGET_BUILD_VARIANT=eng
TARGET_BUILD_TYPE=release
TARGET_BUILD_APPS=
TARGET_ARCH=arm
TARGET_ARCH_VARIANT=armv7-a
HOST_ARCH=x86
HOST_OS=linux
HOST_OS_EXTRA=Linux-3.13.0-29-generic-x86_64-with-Ubuntu-14.04-trusty
HOST_BUILD_TYPE=release
BUILD_ID=JZO54K
OUT_DIR=/home/blttalas/android-sdk-linux/platform-tools/out
============================================
Checking build tools versions...
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You are attempting to build with an unsupported version
of java.
 
Your version is: java version "1.7.0_55".
The correct version is: Java SE 1.6.
 
Please follow the machine setup instructions at
    https://source.android.com/source/download.html
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************************************************************
You are attempting to build with the incorrect version
of javac.
 
Your version is: javac 1.7.0_55.
The correct version is: 1.6.
 
Please follow the machine setup instructions at
    https://source.android.com/source/download.html
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