Ubuntu 16.04 安装 JDK 和 Open Jdk默认JDK 安装相对比较轻松，但如果想调整 OpenSdk 版本可就有点儿麻烦， 特别是 OpenJdk7 。常规安装 见下方附录（How to download and install prebuilt OpenJDK packages）
默认JDK 安装：
sudo apt-get update
sudo apt-get install default-jre
Oracle JDK 安装：
设置 PPA
sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
JDK6 ：
sudo apt-get install oracle-java6-installer
JDK 7：
sudo apt-get install oracle-java7-installer
JDK 8
sudo apt-get install oracle-java8-installer
OpenJdk 7安装：
sudo add-apt-repository ppa:openjdk-r/ppa
sudo apt-get update
sudo apt-get install openjdk-7-jdk
版本之间切换
update-alternatives --config java
update-alternatives --config javac
附：How to download and install prebuilt OpenJDK packages
JDK 8
Debian, Ubuntu, etc.
On the command line, type:
$ sudo apt-get install openjdk-8-jre
The openjdk-8-jre package contains just the Java Runtime Environment. If you want to develop Java programs then please install the openjdk-8-jdk package.
Fedora, Oracle Linux, Red Hat Enterprise Linux, etc.
On the command line, type:
$ su -c "yum install java-1.8.0-openjdk"
The java-1.8.0-openjdk package contains just the Java Runtime Environment. If you want to develop Java programs then install the java-1.8.0-openjdk-devel package.
JDK 7
Debian, Ubuntu, etc.
On the command line, type:
$ sudo apt-get install openjdk-7-jre
The openjdk-7-jre package contains just the Java Runtime Environment. If you want to develop Java programs then install the openjdk-7-jdk package.
Fedora, Oracle Linux, Red Hat Enterprise Linux, etc.
On the command line, type:
$ su -c "yum install java-1.7.0-openjdk"
The java-1.7.0-openjdk package contains just the Java Runtime Environment. If you want to develop Java programs then install the java-1.7.0-openjdk-devel package.
JDK 6
Debian, Ubuntu, etc.
On the command line, type:
$ sudo apt-get install openjdk-6-jre
The openjdk-6-jre package contains just the Java Runtime Environment. If you want to develop Java programs then install the openjdk-6-jdk package.
Fedora, Oracle Linux, Red Hat Enterprise Linux, etc.
On the command line, type:
$ su -c "yum install java-1.6.0-openjdk"
The java-1.6.0-openjdk package contains just the Java Runtime Environment. If you want to develop Java programs then install the java-1.6.0-openjdk-devel package.
BSD Port
For a list of pointers to packages of the BSD Port（http://openjdk.java.net/projects/bsd-port/） for DragonFly BSD, FreeBSD, Mac OS X, NetBSD and OpenBSD, please see the BSD porting Project's wiki page（http://wiki.openjdk.java.net/display/BSDPort/Main）.