查看原版本

java -version

显示如下

java version "1.7.0_101"
OpenJDK Runtime Environment (IcedTea 2.6.6) (7u101-2.6.6-0ubuntu0.14.04.1)
OpenJDK 64-Bit Server VM (build 24.95-b01, mixed mode)

安装 opensdk 8

add-apt-repository ppa:openjdk-r/ppa
apt-get update
apt-get install openjdk-8-jdk

列出已经安装的Java版本

update-java-alternatives -l

显示如下：

java-1.7.0-openjdk-amd64 1071 /usr/lib/jvm/java-1.7.0-openjdk-amd64
java-1.8.0-openjdk-amd64 1069 /usr/lib/jvm/java-1.8.0-openjdk-amd64

手动切换版本

update-alternatives --config java

选择java-8-openjdk-amd64即可

    There are 2 choices for the alternative java (providing /usr/bin/java).

      Selection    Path                                            Priority   Status
    ------------------------------------------------------------
      0            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1071      auto mode
      1            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1071      manual mode
    * 2            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1069      manual mode

    Press enter to keep the current choice[*], or type selection number: 2