Question

(Returning Error Indicators from Metbods) Modify the set methods in class Time2 of Fig. 8.5 to return appropriate error values if an attempt is made to set one of the instance variables hour, minute or second of an object of class Time to an invalid value. [Hint: Use boolean return types on cach method.] Write a program that tests these new set methods and outputs error messages when incorrect values are supplied.

Short answer

Modify the set methods to return boolean values for input validation. Use a test program to verify changes.

Step-by-step solution

Review the Time2 Class

Examine the Time2 class in Fig. 8.5. Identify the member variables hour, minute, and second, and the corresponding set methods for each. These methods will need to be updated to handle invalid input.

Modify setHour Method

Update the setHour method to return a boolean value. The method should first check if the provided hour is within the valid range (0-23). If it is valid, set the hour variable and return true. If not, return false to indicate an error.

Modify setMinute Method

Alter the setMinute method to include a boolean return type. Check if the minute value is within the valid range (0-59). If the input is valid, set the minute variable and return true. If the value is invalid, return false.

Modify setSecond Method

Update the setSecond method similarly. Ensure it has a boolean return type and validate the input against the range (0-59). If valid, set the second variable and return true; otherwise, return false for an incorrect input.

Implement a Test Program

Write a test program that creates an instance of the Time2 class. Attempt to set invalid and valid values for hour, minute, and second using the updated set methods. Output an error message if any of the methods return false, indicating an invalid input.

Key concepts

Error Handling

Error handling is an important concept in Java that ensures programs can manage unexpected inputs or situations gracefully. In the context of object-oriented programming, it's about providing mechanisms to deal with errors without crashing the application. By anticipating and catching errors, developers can ensure the program behaves predictably.

One common approach to handling errors involves checking inputs before using them. In the exercise, the task is to modify set methods to return error indicators. This can be achieved by using boolean values. These return types will help identify whether an operation was successful. For instance:

• Return `true` if the input is valid and the method executes as expected.
• Return `false` if the input is invalid, signaling an error.

This way, the calling function can react appropriately, such as showing an error message to the user, instead of the program failing unexpectedly. This enhances the robustness and user-friendliness of the software.

Methods in Java

Methods in Java are blocks of code designed to perform specific tasks and can be reused across different parts of a program. They promote code modularity and readability. Designating methods with return types and parameters is crucial as it defines what type of data a method will return or accept.

In Java, a method can return various data types like `int`, `boolean`, `String`, etc. The exercise requires altering methods to return a `boolean` type to indicate success or failure in setting values of hour, minute, or second. It's a strategy that combines code function and error handling effectively.

Generally, methods in Java are defined with a specific signature consisting of the access modifier, return type, method name, and parameter list. For example:

• `public boolean setHour(int hour)` - This declares a method that attempts to set the hour and returns a boolean indicating the operation's success.

Effective use of methods aids not only in executing code tasks but also in organizing overall program structure.

Object-Oriented Programming

Object-oriented programming (OOP) is a paradigm in software development that structures programs into objects. Each object can contain data, in the form of fields, and code, in the form of methods. Java is a strongly object-oriented language, emphasizing the creation and interaction of these objects.

The primary focus of OOP is encapsulation, inheritance, and polymorphism. Encapsulation allows for bundling data with the methods that operate on that data, while inheritance lets new classes adopt properties of existing ones. Polymorphism enables a single interface to represent different underlying forms.

In the `Time2` class example, you see how encapsulation allows the inclusion of validation logic within the setter methods. These setter methods interact directly with the object's data, ensuring valid states only. By modifying these methods to return a boolean, it brings in a layer of error checking while retaining the class's encapsulated nature.

• Encapsulation is demonstrated by using private fields and public methods.
• Inheritance could be utilized to extend time-related functionality in further subclasses if needed.

Thus, OOP in Java helps to create a flexible and maintainable codebase.

Java Boolean Return Types

Boolean return types in Java offer a straightforward way to implement error checking in methods, especially where validation is concerned. A boolean type in Java can only have two values: `true` or `false`, representing a binary state.

The exercise's use of boolean return types in setter methods allows for checking the validity of input values. If the value is within the valid range:

• The method returns `true`, signifying the task was successful.
• If not, it returns `false`, alerting the calling function to handle the situation accordingly.

This approach is concise and effective for error signaling, allowing the calling code to take necessary action, such as prompting a user or logging the error. It facilitates clear communication between different parts of a program and enhances overall program robustness.

When designing methods, deciding on appropriate return types like boolean helps craft more reliable and understandable code, aiding in programmatic flow control.