1.查看系統(tǒng)信息
命令： cat /proc/version
Linux version 3.2.0-29-generic (buildd@allspice) (gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) ) #46-Ubuntu SMP ...... UTC 2012
2.查看系統(tǒng)是32還是64位
命令：getconf LONG_BIT
64
3.查看系統(tǒng)是否已經(jīng)安裝有jdk
命令：java -version
java version "1.6.0_45"
Java(TM) SE Runtime Environment (build 1.6.0_45-b06)
Java HotSpot(TM) 64-Bit Server VM (build 20.45-b01, mixed mode)
4.完整卸載系統(tǒng)上的jdk/jre
命令1：卸載openjdk（注意不是oracle jdk）
若要卸載默認的openjdk：sudo apt-get purge openjdk-*
只看最后一行
xxx upgraded, xxx newly installed, xxx to remove and 123 not upgraded.
命令2：卸載oracle jdk6
http://askubuntu.com/questions/117543/how-to-remove-oracle-jdk
whereis java
java: /usr/bin/java /usr/local/java /usr/share/java /opt/jdk1.6.0_45/bin/java
sudo rm -r /opt/jdk1.6.0_45/
sudo rm -rf /usr/local/java
sudo?rm -rf /usr/share/java
5.創(chuàng)建一個文件夾用來存放jdk和jre
sudo mkdir -p /usr/local/java
6.官網(wǎng)下載jdk 根據(jù)系統(tǒng)版本
因為我是64位，并且需要指定安裝目錄，所以選擇了壓縮版tar.gz
7.使用類似FileZilla的工具上傳jdk
8.安裝
命令：sudo tar xvzf jdk-8u121-linux-x64.tar.gz
內(nèi)容太多不方便展示...
9.安裝好以后進行JAVA_HOME配置
sudo gedit /etc/profile
或者
sudo nano /etc/profile
JAVA_HOME=/usr/local/java/jdk1.8.0_121
JRE_HOME=/usr/local/java/jre1.8.0_121 (如果只下載了jdk：/usr/local/java/jdk1.8.0_121/jre)
PATH=$PATH:$JRE_HOME/bin:$JAVA_HOME/bin
export JAVA_HOME
export JRE_HOME
export PATH
按照最下面的命令提示：寫完保存：ctrl+o ?ctrl+x
10.安裝的3條命令：
sudo update-alternatives --install "/usr/bin/java" "java" "/usr/local/java/jdk1.8.0_121/bin/java" 1
update-alternatives: renaming java link from /usr/bin/java to /usr/local/java.
update-alternatives: warning: forcing reinstallation of alternative /usr/local/java/jdk1.8.0_121/bin/java because link group java is broken.
update-alternatives: warning: not replacing /usr/local/java with a link.
警告??可以忽略，保險起見可以再執(zhí)行一次，就不會報錯了
sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/local/java/jdk1.8.0_121/bin/javac" 1
sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/local/java/jdk1.8.0_121/bin/javaws" 1
java -version
java version "1.8.0_121"
Java(TM) SE Runtime Environment (build 1.8.0_121-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)
參考資料：
http://www.lxweimin.com/u/064e496ecbec
http://www.wikihow.com/Install-Oracle-Java-on-Ubuntu-Linux
