Off topic:how can I remove java 1.8 from my ubuntu 14.04

Question

[Kurban]

Tried Trinity for de novo assembly, but it requires java 1.7:

kurban@kurban-X550VC:~/Desktop/Trinity$ ~/Downloads/trinityrnaseq-2.0.6/Trinity --seqType fq --left R1.fq --right R2.fq --CPU 3 --max_memory 3G
Error, Trinity requires access to Java version 1.7.  Currently installed version is: java version "1.8.0_40"
Java(TM) SE Runtime Environment (build 1.8.0_40-b25)
Java HotSpot(TM) 64-Bit Server VM (build 25.40-b25, mixed mode)
kurban@kurban-X550VC:~/Desktop/Trinity$ rpm -qa jdk
kurban@kurban-X550VC:~/Desktop/Trinity$ sudo rpm -qa jdk
kurban@kurban-X550VC:~/Desktop/Trinity$

And I tried to remove my current version java fro several hours, now its almost dawn here, but I still could not remove it.

Have anybody encountered it before. Please give me some suggestions!