新装的mac 系统10.10 ，jdk是1.8，因为一些工具要使用 jdk 6，以下是设置过程
查看版本
java -version
查看java是再哪：在/usr/bin/java
whereis java
cd /usr/bin
ls -all | grep java
lrwxr-xr-x 1 root wheel 74 9 23 00:23 java -> /System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands/java
lrwxr-xr-x 1 root wheel 75 9 23 00:23 javac -> /System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands/javac
lrwxr-xr-x 1 root wheel 77 9 23 00:23 javadoc -> /System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands/javadoc
lrwxr-xr-x 1 root wheel 75 9 23 00:23 javah -> /System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands/javah
lrwxr-xr-x 1 root wheel 75 9 23 00:23 javap -> /System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands/javap
lrwxr-xr-x 1 root wheel 76 9 23 00:23 javaws -> /System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands/javaws
都是软链接
cd /System/Library/Frameworks/JavaVM.framework/Versions/
ls -all
drwxr-xr-x root wheel : .
drwxr-xr-x root wheel : ..
lrwxr-xr-x root wheel : 1.4 -> CurrentJDK
lrwxr-xr-x root wheel : 1.4. -> CurrentJDK
lrwxr-xr-x root wheel : 1.5 -> CurrentJDK
lrwxr-xr-x root wheel : 1.5. -> CurrentJDK
lrwxr-xr-x root wheel : 1.6 -> CurrentJDK
lrwxr-xr-x root wheel : 1.6. -> CurrentJDK
drwxr-xr-x root wheel : A
lrwxr-xr-x root wheel : Current -> A
lrwxr-xr-x root wheel : CurrentJDK -> /System/Library/Java/JavaVirtualMachines/1.6..jdk/Contents
Current 指向了A，A是1.8的
我自己安装的1.6 在CurrentJDK，删除以前的软链接，执行CurrentJDK，就Ok了，如果要还原到1.8 就重新建立软链接
sudo rm -rf Current ln -s CurrentJDK Current ls -all
total
drwxr-xr-x root wheel : .
drwxr-xr-x root wheel : ..
lrwxr-xr-x root wheel : 1.4 -> CurrentJDK
lrwxr-xr-x root wheel : 1.4. -> CurrentJDK
lrwxr-xr-x root wheel : 1.5 -> CurrentJDK
lrwxr-xr-x root wheel : 1.5. -> CurrentJDK
lrwxr-xr-x root wheel : 1.6 -> CurrentJDK
lrwxr-xr-x root wheel : 1.6. -> CurrentJDK
drwxr-xr-x root wheel : A
lrwxr-xr-x root wheel : Current -> CurrentJDK
lrwxr-xr-x root wheel : CurrentJDK -> /System/Library/Java/JavaVirtualMachines/1.6..jdk/Contents java -version
java version "1.6.0_65"
Java(TM) SE Runtime Environment (build 1.6.0_65-b14-466.1-11M4716)
Java HotSpot(TM) -Bit Server VM (build 20.65-b04-466.1, mixed mode)
Mac JDK 1.6 安装 ：是否有毒，自行判断，因为xcodeGoast，心里有点怕怕的。
http://download.csdn.net/download/zw_yuyan/8350587