问题:

jalen_chu@jalen:~$ javac
程序 'javac' 已包含在下列软件包中:
* default-jdk
* ecj
* gcj-4.8-jdk
* openjdk-7-jdk
* gcj-4.6-jdk
* openjdk-6-jdk
  请尝试:sudo apt-get install <选定的软件包>

(java -version 同上)

方案:

输入:$ sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.7.0_75/bin/javac 300

返回:update-alternatives: using /usr/lib/jvm/jdk1.7.0_75/bin/javac to provide /usr/bin/javac (javac) in 自动模式

javac

...

输入:$ sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.7.0_75/bin/java 300

返回:update-alternatives: using /usr/lib/jvm/jdk1.7.0_75/bin/java to provide /usr/bin/java (java) in 自动模式

java -version