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You can completely remove the OpenJDK and fresh Install Oracle Java JDK by the following steps:

Remove OpenJDK completely by this command:

# sudo apt-get purge openjdk-\*

Download the Oracle Java JDK here.

www.oracle.com/technetwork/java/javase/downloads/index.html 

Note: download appropriate file, for example if your system is x64 Ubuntu (i.e, Debian) the download file is named like this: jdk-8u51-linux-x64.tar.gz

To find which version is your OS, check here

Create a folder named java in /usr/local/by this command:

# sudo mkdir -p /usr/local/java

Copy the Downloaded file in the directory /usr/local/java. To do this, cd into directory where downloaded file is located and use this command for copying that file to /usr/local/java/:

# sudo cp -r jdk-8u51-linux-x64.tar.gz /usr/local/java/

CD into /usr/local/java/ directory and extract that copied file by using this command:

# sudo tar xvzf jdk-8u51-linux-x64.tar.gz

After extraction you must see a folder named jdk1.8.0_51.

Update PATH file by opening /etc/profile file by the command 

# sudo nano /etc/profile and paste the following at the end of the file:

JAVA_HOME=/usr/local/java/jdk1.8.0_51
PATH=$PATH:$HOME/bin:$JAVA_HOME/bin
export JAVA_HOME
export PATH

Save and exit.

Tell the system that the new Oracle Java version is available by the following commands:

# sudo update-alternatives --install "/usr/bin/java" "java" "/usr/local/java/jdk1.8.0_51/bin/java" 1
# sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/local/java/jdk1.8.0_51/bin/javac" 1
# sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/local/java/jdk1.8.0_51/bin/javaws" 1

Make Oracle Java JDK as default by this following commands:

# sudo update-alternatives --set java /usr/local/java/jdk1.8.0_51/bin/java
# sudo update-alternatives --set javac /usr/local/java/jdk1.8.0_51/bin/javac
# sudo update-alternatives --set javaws /usr/local/java/jdk1.8.0_51/bin/javaws

Reload sytem wide PATH /etc/profile by this command:

# source /etc/profile

Reboot your system.

Check Java JDK version by java -version command . If installation is succesful, it will display like the following:

java version "1.8.0_51"
Java(TM) SE Runtime Environment (build 1.8.0_51-xxx)
Java HotSpot(TM) Server VM (build 25.51-xxx, mixed mode)

That's it!