Unable to locate package错误解决办法以及jdk的切换

问题分析以及解决方法

在ubuntu上安装Open JDK 8时遇到问题：

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

多数是因为apt更新源的问题，更新一下源就ok了

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

多个jdk切换方法

首先我们看下系统已经安装的或在用的JDK

$ update-java-alternatives -l
java-1.7.0-openjdk-amd64 1071 /usr/lib/jvm/java-1.7.0-openjdk-amd64

现在安装jdk8之后变成

$ update-java-alternatives -l
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

下面我们用“update-alternatives --config java” 指令切换默认jdk

$ sudo update-alternatives --config java
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:

选择你要使用的JDK：比如1然后回车java就ok了，同上方法将javac、javap、javadoc更换即可：

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