Challenge:

Bidirectional data flow, user-provided text input.

Criteria:

• The task is to build a frame containing 2 textfields representing the temperature in Celsius and Fahrenheit.
• Initially, both textfields are empty.
• When the user enters a numerical value into a textfield, the corresponding value in the other is automatically updated.
• When the user enters a non-numerical string into a textfield, the value in the other is not updated.
• Formula for converting a temperature from Celsius to Fahrenheit: F = C * (9/5) + 32
• Formula for converting a temperature from Fahrenheit to Celsius: C = (F - 32) * (5/9)

Temperature Converter increases the complexity of Counter by having bidirectional data flow between the Celsius and Fahrenheit inputs and the need to check the user input for validity. A good solution will make the bidirectional dependency very clear with minimal boilerplate code.

Temperature Converter is inspired by the Celsius/Fahrenheit converter from the book Programming in Scala. It is such a widespread example—sometimes also in the form of a currency converter—that one could give a thousand references. The same is true for the Counter task.