sudo mkdir /usr/lib/jvm
sudo tar -zxvf jdk-xxx.gz -C /usr/lib/jvm

sudo vim ~/.bashrc

export JAVA_HOME=/usr/lib/jvm/jdk1.8.0_151
export JRE_HOME=${JAVA_HOME}/jre
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib
export PATH=${JAVA_HOME}/bin:$PATH

~/.bashrc

sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.8.0_151/bin/java 300 # 数字表示优先级
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.8.0_151/bin/javac 300
sudo update-alternatives --install /usr/bin/jar jar /usr/lib/jvm/jdk1.8.0_151/bin/jar 300
sudo update-alternatives --install /usr/bin/javah javah /usr/lib/jvm/jdk1.8.0_151/bin/javah 300
sudo update-alternatives --install /usr/bin/javap javap /usr/lib/jvm/jdk1.8.0_151/bin/javap 300

sudo update-alternatives --config java
# 选择合适的JDK

sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update

sudo apt-get install oracle-java8-installer

1. ppa有可能会失效，若失效则再找过一个
2. 如果installer下载很慢，可以中断，然后下载好对应的jdk的tar.gz包。放在 /var/cache/oracle-jdk8-installer 目录下。然后再安装一次installer，它会默认使用下载好的压缩包。