E: Unable to locate package openjdk-8-jdk 及java version 切换

在unbuntu14.04系统上安装 Open JDK 8 时遇到了如下问题：

$ sudo apt-get install openjdk--jdk
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package openjdk-8-jdk

解决方法：

As you can see I only have java 1.7 installed (on a Ubuntu 14.04 machine).

$ update-java-alternatives -l
java-1.7.-openjdk-amd64  /usr/lib/jvm/java-1.7.-openjdk-amd64

To install Java 8, I did,

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

Afterwards, now I have java 7 and 8,

$ update-java-alternatives -l
java-1.7.-openjdk-amd64  /usr/lib/jvm/java-1.7.-openjdk-amd64
java-1.8.-openjdk-amd64  /usr/lib/jvm/java-1.8.-openjdk-amd64

How to switch between different versions?

run the follwing command from the terminal:

$ sudo update-alternatives --config java
There are  choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                            Priority   Status
------------------------------------------------------------
              /usr/lib/jvm/java--openjdk-amd64/jre/bin/java         auto mode
              /usr/lib/jvm/java--openjdk-amd64/jre/bin/java         manual mode
*             /usr/lib/jvm/java--openjdk-amd64/jre/bin/java         manual mode

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

As you can see I'm running open jdk 8. To switch to to jdk 7, press 1 and hit the Enter key. Do the same for javac,javap,javadoc as well with,:

$ sudo update-alternatives --config javac
$ sudo update-alternatives --config javap
$ sudo update-alternatives --config javadoc

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