Question

Assume the following variable declaration exists in a program: double number \(=123456.789\) Write a statement that uses system.out.printf to display the value of the number variable left-justified, with comma separators, in a field that is 20 spaces wide, rounded to two decimal places.

Short answer

Answer: `System.out.printf("%-20,.2f", number);`

Step-by-step solution

Create a Java print statement

To display the value of 'number' according to the given requirements, use the following Java print statement: ```java System.out.printf("%-20,.2f", number); ``` This will display the value of 'number' (123456.789) left-justified, with comma separators, in a field that is 20 spaces wide, rounded to two decimal places.

Key concepts

Java Programming

Java is a versatile and powerful programming language used for developing a wide array of applications, from mobile apps to enterprise software. Understanding Java syntax and core concepts is essential for tackling assignments and crafting effective code. In Java, variables like double number = 123456.789; store data, which can be manipulated or displayed. Our task involves using a method to output the double's value in a specific format, showcasing the importance of controlling data representation in Java applications.

Essential to this is using the correct Java methods and syntax, such as System.out.printf, to achieve the desired output. Being proficient in Java means knowing how to use such methods to display data in a way that's readable and meets specific requirements, whether it's for a user interface, a report, or debugging purposes.

String Formatting

In Java, formatting strings is a critical skill that enables developers to present data in a user-friendly way. String formatting involves specifying the arrangement and appearance of data within a string. The format specifiers, like %-20,.2f used in our exercise solution, dictate how the variable should be displayed.

Understanding Format Specifiers

Each specifier has a purpose – for instance, the hyphen - in our example indicates left-justification. The number 20 denotes the width of the output field, ensuring that the formatted number fits into a column with consistent width.
Furthermore, the , tells Java to include comma separators for thousands, millions, and so forth, while .2 indicates the precision of the floating-point number, rounding it to two decimal places. Mastery of string formatting leads to clearer data presentation in Java programs.

System.out.printf

The System.out.printf method in Java is a powerful feature for formatting and printing strings with different types of data – numbers, characters, dates, and more. This method allows for fine-grained control over how the information is displayed through the use of formatted strings.

In practice, System.out.printf uses format specifiers to include variables within a string in a formatted manner, making it possible to construct complex outputs with ease. The placeholders are replaced by the values of variables when the code is executed, adhering to any formatting rules specified.

Format Specifiers in Print Statements

Learning to use System.out.printf efficiently is crucial for Java developers. Detailed knowledge of format specifiers can greatly enhance the readability and presentation of output, which is especially useful when the visual layout of the presented data is important, such as in the display of tables or reports.