I'll try to answer all your questions, but please break them into separate Q&As in the future. It makes it easier for one person to answer.

1. You seem to have a bit of a misunderstanding in regards to 32-bit. x86 is actually 32-bit. x86 is named after a line of old Intel CPUs (I think), but they didn't really have anything to name 64-bit after, so it became x64.

   • Get the x86 version

2. You'll have to adapt the file names a bit, since Java versions have changed, but this Ask Ubuntu Q&A has very extensive installation instructions: How can I install Sun/Oracle's proprietary Java JDK 6/7/8 or JRE?.

3. As for default Java version, you need to have the one you want as default installed, and then you need to select it as the default. How to set default Java version?.

   • The command you want, since it looks like you're dealing with javac, is:

     sudo update-alternatives --config javac
     

   • Replacing javac with java will allow you to change defaults there too.

Honestly, I'm having a hard time understanding your question fully, and I see you don't speak English natively. Hopefully, what I have below will make the whole thing easier.

There's an alternative to Oracle's JDK, called OpenJDK. It's a very simple installation, and I believe it sets itself as the default Java version. To install:

sudo apt-get install openjdk-8-jdk