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jdk interview questions

Top jdk frequently asked interview questions

Which Java package should I use: OpenJDK or Oracle JDK?

I'm new to Java development under Ubuntu. When I typed javac in the terminal, it prompted me to install OpenJDK and a bunch of other JDKs. I want to know if there is any difference between OpenJDK 7 and Oracle's JDK 7. Are they basically the same? Thanks.


Source: (StackOverflow)

How to remove Oracle JDK

I didn't find article any related articles How to remove Oracle JDK there are some related articles but they didn't solve the problem.

I installed Oracle JDK tarball file from Oracle site by following this article How do I install Oracle Java JDK 7. It was very helpful. but I don't what I should do to uninstall Oracle JDK.


Source: (StackOverflow)

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"No such file or directory" when invoking java

I'm trying to re-install Oracle JDK 7 32 bit to 64 bit Ubuntu (previously 64 bit JDK was installed). JDK is currently present at /usr/lib/jvm/jdk1.7.0. I invoke

sudo update-alternatives --remove "java" "/usr/lib/jvm/jdk1.7.0/bin/java"
sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/jdk1.7.0/bin/java" 1

And then:

/usr/lib/jvm/jdk1.7.0/bin$ java
bash: /usr/bin/java: No such file or directory

Why java can't be invoked?


Source: (StackOverflow)

How can I install Sun/Oracle's proprietary Java JDK 6/7/8 or JRE?

I want to install Oracle's JRE and to update to the latest version with the Software Updater when they released. Is there a Ubuntu package that is provided by Canonical or Oracle?

Before release Java 7, I followed this way to install Java 6.

But it doesn't work for Java 7. There is no package sun-java7-xxx. How can you install Java 7?


Source: (StackOverflow)

Where is the Oracle java jdk keystore located?

Installed Oracle Java with the webupd8 ppa and need to tweak some policy settings (access to clipboard specifically)

webUpd8 plug: http://www.webupd8.org/2011/09/how-to-install-oracle-java-7-jdk-in.html

(these guys have done alot for the Ubuntu community)

Previously it was under /etc/java-6-oracle

Google doesn't have any answers on this one -- any ideas?


Source: (StackOverflow)

installed jdk by and have Error: Could not create the Java Virtual Machine

I am getting my new laptop going and went to install the latest oracle JDK 7u25. I followed the instructions on this site to do it.

Afterwards when I type java --version in the terminal I get the error:

Error: Could not create the Java Virtual Machine

I tried reinstalling it via a different method but the error wont go away. I am running Ubuntu 12.04 64bit.


Source: (StackOverflow)

How do I install Oracle Java JDK 7? [duplicate]

This question already has an answer here:

If I downloaded the latest JDK from Oracle, do I just download the .tar file and extract it to /usr/lib/jvm/?


Source: (StackOverflow)

How do I install Oracle JDK 6? [duplicate]

This question already has an answer here:

Most of the software is not thoroughly tested with Java 7 and I would like to install Oracle's JDK 6.0 on Ubuntu 11.10.

Could someone please provide me the instructions for the same?


Source: (StackOverflow)

Setting JDK 7 as default

 four@twenty:~$ file /etc/alternatives/java /etc/alternatives/javac
 /etc/alternatives/java:symbolic link to `/usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java'
 /etc/alternatives/javac:symbolic link to `/usr/lib/jvm/java-6-openjdk-amd64/bin/javac'

Forgive my noobishness but Im interpreting that as the runtime environment using Java 7 but the compiler using 6?

Is this right and if so how can I set it to use 7?

Thanks :)


Source: (StackOverflow)

How can I tell what version of Java I have installed?

I want to start toying around with java (eventually getting to the point where I can write basic little programs for android or web), but I've managed to have java messed up on my computer (from past experiments).

I'm not sure which version of java I have, and would like to know if there is a command to see the version of java that is installed and active. Also, which version works best? All this on 32bit Ubuntu 12.04

EDIT:
Ok, so it seems like I have both openjdk 6 and 7, with openjdk 7 in use. I want to use openjdk 7, so how do I uninstall openjdk 6? Is just via USC good enough or is there a command that should be run?


Source: (StackOverflow)

Specify JDK for tomcat7

I have installed tomcat7 (using apt-get install) and whenever I want to start tomcat7 it says :

* no JDK found - please set JAVA_HOME

I have set JAVA_HOME in my bash.bashrc and also in ~/.bashrc and when I issue echo $JAVA_HOME I clearly see that this variable is pointing to my jdk's root folder. Can someone help me with this please?

Thanks


Source: (StackOverflow)

'tools.jar' is not in IDEA classpath

I am a new user of Linux, it has been recommended to me by my friend.

He told me to install software called IntelliJ Idea IDE.

Well I have been following the tutorial. But now when I try to open "idea.sh", an error message pops-up:

'tools.jar' is not in IDEA classpath.
Please ensure JAVA_HOME points to JDK rather than JRE.

Please remember that I'm new to Ubuntu and I'm planning for a nice long stay once I get myself into it :)

Also I do not know if I am running a correct Java6 JDK. When I do java -version, this is what I get:

java version "1.6.0_23"
OpenJDK Runtime Environment (IcedTea6 1.11pre) (6b23~pre10-0ubuntu5)
OpenJDK 64-Bit Server VM (build 20.0-b11, mixed mode)

Thank You for reading this and I hope I will get a nice response.


Source: (StackOverflow)

How to set the JDK for Android Studio?

I can't compile a default new project for Android 2.1 because(?) the JDK used by Android Studio is JDK 1.7 but it should be JDK 1.6.

To change it I go to File -> Project Structure and try to find the JDK 1.6 location.

But when I select its directory and press OK I get the following error:

Please choose a valid JDK directory

Please choose a valid JDK directory

As you can see on the screenshoot I'm trying to set Java 6 OpenJDK 64-bits as the new JDK.

What can I do? Isn't Android Studio compatible with OpenJDK and should I use Oracle JDK instead?


Source: (StackOverflow)

Setup and install IntelliJ with JDK

Is there any scripts for downloading and installing IntelliJ with JavaJDK or OpenJDK?

I don't know how I did it before using Ubuntu 12.10 but I'm now on a fresh 13.04 install and I have been looking around for an all in one script, or some scripts I can cobble together

I have the two links detailed that I think will be handy, can anyone else add to this please?

How do I install Oracle Java JDK 7?

Install Oracle Java 7 in Ubuntu via PPA Repository

Update: I have now found you can install IntelliJ through the Ubuntu software centre, so although this was a nice learning exercise for me it's not really relevant any more. Thanks to everyone that contributed.


Source: (StackOverflow)

How do I make java default to a manually installed JRE/JDK?

I have Ubuntu 12.04 amd64 installed on my machine, on the previous versions of Ubuntu it was deadly easy, now there is this command update-java-alternatives with a really bad man page.

I just have my JDK unpacked on a mounted partition like /media/mydisk/jdk, how i can force the use of that JDK instead of the one that comes in the Ubuntu repository?

What is the logic behind this update-java-alternatives ?


Source: (StackOverflow)