Steps to resolve Error:-

1.Go to This PC.

2. Go to Local Disk(C) then go to Programme files.

3.Double click on Java. it show jdk1.8.0_121 (Double click on it)

4.copy path of JDK.

5.Repeat steps 1 to 3.

6.Double click on bin folder. then copy path of bin folder.

7.Go to This PC then right click on This PC ==>Properties==>go to Advance system Settings==>go to Environmental Variable==>Go to Edit.

8.write Variable name : Java_Home and Variable Value : Paste Path of JDK(step 4 path).

9.Go to This PC then right click on This PC ==>Properties==>go to Advance system Settings==>go to Environmental Variable==>Click on the New button (In System variable)

10.Paste Path of bin Folder(Step 6 path and click on move -up to set on the top).

Now , you write Javac on Cmd it doesn't show any error.