This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
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As for your issue, the error message you get is pretty straightforward. You are trying to print the value of variable area but you haven't declared it. However, you can get an area of the rectangle by invoking area() method on an instance of the class representing a rectangle. The method is invoked as: classInstance.methodName().