$ sudo apt install openjdk-9-jdk
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  junit libaopalliance-java libapache-pom-java libasm4-java
  libatinject-jsr330-api-java libbsh-java libcdi-api-java libcglib3-java
  libclassworlds-java libcommons-cli-java libcommons-codec-java
  libcommons-httpclient-java libcommons-io-java libcommons-lang-java
  libcommons-lang3-java libcommons-logging-java libcommons-net-java
  libcommons-net2-java libcommons-parent-java libdom4j-java libdoxia-core-java
  libeclipse-aether-java libgeronimo-interceptor-3.0-spec-java libguava-java
  libguice-java libhamcrest-java libhttpclient-java libhttpcore-java
  libjaxen-java libjaxp1.3-java libjdom1-java libjetty-java libjsch-java
  libjsoup-java libjsr305-java liblog4j1.2-java libmaven-parent-java
  libmaven2-core-java libobjenesis-java libplexus-ant-factory-java
  libplexus-archiver-java libplexus-bsh-factory-java libplexus-cipher-java
  libplexus-classworlds-java libplexus-classworlds2-java libplexus-cli-java
  libplexus-component-annotations-java libplexus-component-metadata-java
  libplexus-container-default-java libplexus-container-default1.5-java
  libplexus-containers-java libplexus-containers1.5-java
  libplexus-interactivity-api-java libplexus-interpolation-java
  libplexus-io-java libplexus-sec-dispatcher-java libplexus-utils-java
  libplexus-utils2-java libqdox2-java libservlet2.5-java libservlet3.1-java
  libsisu-inject-java libsisu-plexus-java libslf4j-java libwagon-java
  libxalan2-java libxbean-java libxerces2-java libxml-commons-external-java
  libxml-commons-resolver1.1-java libxom-java libxpp2-java libxpp3-java
Use 'sudo apt autoremove' to remove them.
Suggested packages:
  openjdk-9-demo openjdk-9-source visualvm
The following NEW packages will be installed:
  openjdk-9-jdk
0 upgraded, 1 newly installed, 0 to remove and 141 not upgraded.
5 not fully installed or removed.
Need to get 0 B/16.6 kB of archives.
After this operation, 58.4 kB of additional disk space will be used.
(Reading database ... 257571 files and directories currently installed.)
Preparing to unpack .../openjdk-9-jdk_9~b114-0ubuntu1_amd64.deb ...
Unpacking openjdk-9-jdk:amd64 (9~b114-0ubuntu1) ...
dpkg: error processing archive /var/cache/apt/archives/openjdk-9-jdk_9~b114-0ubuntu1_amd64.deb (--unpack):
 trying to overwrite '/usr/lib/jvm/java-9-openjdk-amd64/include/linux/jawt_md.h', which is also in package openjdk-9-jdk-headless:amd64 9~b114-0ubuntu1
Errors were encountered while processing:
 /var/cache/apt/archives/openjdk-9-jdk_9~b114-0ubuntu1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)