ubuntu下安裝jdk

直接下載jdk壓縮包方式安裝
　分爲5個步驟

1.官網下載JDK

官網地址
　　選擇相應的 .gz包下載

2.解壓縮,放到指定目錄(以jdk-8u221-linux-x64.tar.gz爲例)

創建目錄:

sudo mkdir /usr/lib/jvm

加壓縮到該目錄:

sudo tar -zxvf jdk-8u221-linux-x64.tar.gz -C /usr/lib/jvm

3.修改環境變量:

sudo vim ~/.bashrc
　文件的末尾（GG:直接到底部）追加下面內容:

#set oracle jdk environment
export JAVA_HOME=/usr/lib/jvm/jdk1.8.0_221  ##這裏要注意目錄要換成自己解壓的jdk目錄
export JRE_HOME=${JAVA_HOME}/jre  
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib  
export PATH=${JAVA_HOME}/bin:$PATH  

使環境變量馬上生效

 source ~/.bashrc

4.設置系統默認jdk 版本

sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.8.0_221/bin/java 300  
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.8.0_221/bin/javac 300  
sudo update-alternatives --install /usr/bin/jar jar /usr/lib/jvm/jdk1.8.0_221/bin/jar 300   
sudo update-alternatives --install /usr/bin/javah javah /usr/lib/jvm/jdk1.8.0_221/bin/javah 300   
sudo update-alternatives --install /usr/bin/javap javap /usr/lib/jvm/jdk1.8.0_221/bin/javap 300   

然後執行:

sudo update-alternatives --config java

若是初次安裝jdk,會有下面的提示 

There is only one alternative in link group java (providing /usr/bin/java): /usr/lib/jvm/jdk1.8.0_221/bin/java
Nothing to configure.

否者,選擇合適的jdk

5.測試jdk

java -version

java version "1.8.0_221"
Java(TM) SE Runtime Environment (build 1.8.0_221-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.221-b11, mixed mode)

jdk 安裝成功

ubuntu 兩種下安裝jdk7 jdk8 的方式介紹完畢