This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
I am sorry, i am not ignoring the suggestion and don't mean to say that i am completely right, but instead of adopt the suggestion blindly, i am also interested to know at what point I am wrong so that i can make my concept clear as I am beginner.
And Thank You for Suggestion to You All.
A JScrollPane uses the preferred size of the component in its viewport to determine whether or not to show scrollbars. In your case that component is not the JTextArea but the WestWindow with a preferred size of 330x50. That WestWindow contains the JTextArea without scrollbars because you simply never programmed any to be there. If you would not manually set the preferred size the WestWindow would calculate its preferred size from the JTextArea instead.
In addition to what Rob said, if the scroll pane's viewport component implements the Scrollable interface, the scroll pane's layout manager honors the viewport component's preferences in respect of the preferred viewport size, tracking the viewport width/height and the scrollable increments.