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Chapter 6: Problem 20

Write an application that prompts the user for the radius of a circle and uses a method called circleArea to calculate the area of the circle.

Short Answer

Expert verified
Define the method circleArea to calculate the area using the formula \( \pi r^2 \. Prompt the user for the radius, call circleArea with this radius, and display the calculated area.

Step by step solution

01

Define the circleArea Method

Create a method called circleArea that takes a single parameter (the radius of the circle) and returns the area of the circle. Use the formula for the area of a circle, which is \( \pi r^2 \), where \( r \) is the radius.
02

Prompt the User for the Radius

Write a segment of code that prompts the user to input the radius of the circle. This can be achieved by using a scanner(for Java), input function (for Python), or similar functions in other programming languages.
03

Call the circleArea Method

After receiving the input from the user, call the circleArea method with the user-provided radius as the argument. Store the result in a variable.
04

Display the Result

Print out the result so the user can see the area of the circle. Format the output to make it user-friendly, for example: 'The area of the circle with radius \( r \) is: \( area \)'.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Java Programming
Java is a popular, versatile programming language designed to work across various platforms without the need for recompilation. In Java, programs are compiled into bytecode, which runs on Java Virtual Machines (JVMs), making Java programs platform-independent.

Understanding Java programming involves mastering its syntax, object-oriented principles, and its extensive class libraries that provide support for handling common programming tasks. In educational contexts, Java is widely used to demonstrate concepts because it enforces good programming practices and has a syntax that is relatively easy to understand.
Method Definition
In Java, a method is a block of code that performs a specific task. Defining a method includes specifying its visibility (like public or private), return type, name, and parameters. The circleArea method in our example takes in a radius and returns the circle's area. It encapsulates the area calculation logic, which makes the main program cleaner and the method itself reusable.

Basic Method Structure

Here's a simple illustration:
public double circleArea(double radius) {
  // Method body that returns area
}

Once defined, this method can be called as many times as needed, with different arguments, to perform the calculation for various circles.
User Input Handling
Obtaining user input is a common requirement in many programs. Java handles this through the Scanner class, which can parse primitive types and strings using regular expressions. When the user is prompted for the radius of a circle, a Scanner object can be used to read the input from the console.

Example of User Input

The typical steps for reading user input in Java are:
1. Import the Scanner class.
2. Create a Scanner object.
3. Prompt the user for input.
4. Read the input value using the appropriate method of the Scanner object, like nextDouble() for a double value.
5. Close the Scanner object to avoid resource leaks.
The program proceeds to use this input, passing it to the necessary methods for further processing.
Mathematical Formulas in Programming
Mathematical operations are fundamental in programming, allowing for the performance of calculations like the area of a circle. Programs translate mathematical formulas into code, which can then be executed to solve numerical problems.

In our example, the area of a circle is calculated using the formula: \( \pi r^2 \), where \( \pi \) is a constant and \( r \) represents the radius of the circle supplied by the user. In Java, one can use the predefined constant Math.PI to represent \( \pi \) and apply the multiplication and power operations to compute the area. The resulting value is returned by the method and can be displayed to the user.

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Most popular questions from this chapter

Write a method minimum3 that returns the smallest of three floatingpoint numbers. Use the Math.min method to implement minimum3. Incorporate the method into an application that reads three values from the user, determines the smallest value and displays the result.

Write an application that plays “guess the number” as follows: Your program chooses the number to be guessed by selecting a random integer in the range 1 to 1000. The application displays the prompt Guess a number between 1 and 1000. The player inputs a first guess. If the player's guess is incorrect, your program should display Too high. Try again. or Too low. Try again. to help the player “zero in” on the correct answer. The program should prompt the user for the next guess. When the user enters the correct answer, display Congratulations. You guessed the number!, and allow the user to choose whether to play again. [Note: The guessing technique employed in this problem is similar to a binary search, which is discussed in Chapter 19, Searching, Sorting and Big O.]

Find the error in each of the following program segments. Explain how to correct the error. a) void g() { System.out.println("Inside method g"); void h() { System.out.println("Inside method h"); } } b) int sum(int x, int y) { int result; result = x + y; } c) void f(float a); { float a; System.out.println(a); } d) void product() { int a = 6, b = 5, c = 4, result; result = a * b * c; System.out.printf("Result is %d%n", result); return result; }

Math.floor can be used to round values to the nearest integer—e.g., y = Math.floor(x + 0.5); will round the number x to the nearest integer and assign the result to y. Write an application that reads double values and uses the preceding statement to round each of the numbers to the nearest integer. For each number processed, display both the original number and the rounded number.

Write statements that assign random integers to the variable n in the following ranges: a) 1 ?n ? 2. b) 1 ?n ? 100. c) 0 ?n ? 9. d) 1000 ?n ? 1112. e) –1 ?n ? 1. f) –3 ?n ? 11.
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