1.ubuntu使用的是openjdk，所以我们需要先找到合适的jdk版本。在命令行中输入命令：
$apt-cache search openjdk返回结果列表(因个人电脑而有所不同)：
default-jdk-doc - Standard Java or Java compatible Development Kit (documentation)
…(省略部分显示结果)
openjdk-6-source - OpenJDK Development Kit (JDK) source files
openjdk-7-jre-dcevm - Alternative VM for OpenJDK 7 with enhanced class redefinition
openjdk-7-jre-lib - OpenJDK Java runtime (architecture independent libraries)
openjdk-7-jre-zero - Alternative JVM for OpenJDK, using Zero/Shark
openjdk-8-dbg - Java runtime based on OpenJDK (debugging symbols)
openjdk-8-demo - Java runtime based on OpenJDK (demos and examples)
openjdk-8-doc - OpenJDK Development Kit (JDK) documentation
openjdk-8-jdk - OpenJDK Development Kit (JDK)
openjdk-8-jre - OpenJDK Java runtime, using Hotspot JIT
openjdk-8-jre-headless - OpenJDK Java runtime, using Hotspot JIT (headless)
openjdk-8-jre-jamvm - Alternative JVM for OpenJDK, using JamVM
openjdk-8-jre-zero - Alternative JVM for OpenJDK, using Zero/Shark
openjdk-8-source - OpenJDK Development Kit (JDK) source files
uwsgi-app-integration-plugins - plugins for integration of uWSGI and application
uwsgi-plugin-jvm-openjdk-7 - Java plugin for uWSGI (OpenJDK 7)
2.从搜索的列表里找到我们需要安装的jdk版本，如上面标黑的
openjdk-8-jdk - OpenJDK Development Kit (JDK)
3.输入安装命令，进行安装：
$sudo apt-get install openjdk-8-jdk等待命令行显示“done”，即安装成功过。
4.查看安装结果。输入命令：
$java -version显示结果如下：
openjdk version “1.8.0_91”
OpenJDK Runtime Environment (build 1.8.0_91-8u91-b14-0ubuntu4~15.10.1-b14)
OpenJDK Server VM (build 25.91-b14, mixed mode)
则说明安装成功。
5.安装成功后，还需要配置java_home变量：
1)输入命令：echo $java_home
返回空行；
2）which javac
返回：/usr/bin/javac
3）file /usr/bin/javac
返回：/usr/bin/javac: symbolic link to /etc/alternatives/javac
4）file /etc/alternatives/javac
返回：/etc/alternatives/javac: symbolic link to /usr/lib/jvm/java-8-openjdk-i386/bin/javac
5）file /usr/lib/jvm/java-8-openjdk-i386/bin/javac
返回：/usr/lib/jvm/java-8-openjdk-i386/bin/javac: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=a8eeb948df0418fc8f046910c73713f2b6697a9a, stripped
6）sudo echo export JAVA_HOME=”/usr/lib/jvm/java-8-openjdk-i386/bin”>>~/.bashrc
输入密码；
7）source ~/.bashrc
8）测试命令：gedit ~/.bashrc
查看打开的文件末尾是否成功加入java_home