The entire process of installing JDK In ubuntu (for reference only)

First, download JDK from the http://java.sun.com, my version is jdk1.6.0 _ 12, I download binfile, I will download jdk1.6.0 _ 12. binfile in/usr/lib/JVM/Java
Then, execute: Code: Sudo chmod U + x/usr/lib/JVM/Java/jdk1.6.0 _ 12.bin

Modify binfile permissions to make them executable
Then, executeCode:Sudo/usr/lib/JVM/Java/jdk1.6.0 _ 12.bin

Subtitles will appear. Press enter until yes/no is required for the screen display. Enter y and press Enter. The JDK will be decompressed to the folder to get the JDK 1.6.0 _ 12 directory.
Now that JDK has been installed, configure it below
RunCode:Sudo VI/etc/environment

In environment, the following section appears:Reference:Path = "......:/usr/lib/JVM/Java/jdk1.6.0 _ 12/bin"
Classpath =.:/usr/lib/JVM/Java/jdk1.6.0 _ 12/lib
Java_home =/usr/lib/JVM/Java/jdk1.6.0 _ 12

RunCode:Sudo source/home/ghoul/. bashrc

At this time, the environment variables are successfully set (there are many ways to set the environment variables, not to list them one by one)
Because ubuntu may have a default JDK, such as openjdk, we need to perform the following work to make the JDK installed by default.
RunCode:Update-alternatives -- install/usr/bin/Java/usr/lib/JVM/Java/jdk1.6.0 _ 12/bin/Java 300
Update-alternatives -- install/usr/bin/javac/usr/lib/JVM/Java/jdk1.6.0 _ 12/bin/javac 300

In this step, add the installed JDK to the Java menu.
Then executeCode:Update-alternatives -- config Java

In this step, select the default JDK
In this way, enterCode:Java-version

The system uses Sun Java.