Question

Assume that the double variable number holds the value \(7634869.1 .\) What format pattern would you use with a DecimalforMat object to display the number as \(7,634,869.10 ?\)

Short answer

A: To display a double variable in Java with the desired format, you need to use the DecimalFormat class. First, import the class from the 'java.text' package, then create a DecimalFormat object with the format pattern "#,##0.00". Apply the format pattern to the given double variable using the 'format' method of the DecimalFormat object, and then display the formatted number as a string.

Step-by-step solution

Import DecimalFormat class

First, we need to import the DecimalFormat class from the 'java.text' package. ```java import java.text.DecimalFormat; ```

Create a DecimalFormat object

Next, we need to create a DecimalFormat object with the appropriate format pattern. The format pattern we need is "#,##0.00". This pattern means there should be a comma for every three digits before the decimal point and have two decimal places. ```java DecimalFormat decimalFormat = new DecimalFormat("#,##0.00"); ```

Apply the format pattern to the given number

Now, we will apply the format pattern to the given double variable 'number' using the 'format' method of the DecimalFormat object. ```java double number = 7634869.1; String formattedNumber = decimalFormat.format(number); ```

Display the formatted number

Finally, we will display the formatted number as a string. ```java System.out.println("Formatted number: " + formattedNumber); ``` When you run the program, it will output: ``` Formatted number: 7,634,869.10 ```

Key concepts

Java text package

In Java, dealing with text manipulation and formatting becomes much easier, thanks to the 'java.text' package. This package provides classes that allow you to handle and format different types of text data, such as numbers, dates, and strings in a locale-sensitive manner.

One of the key classes within this package is the DecimalFormat class, which is exceptionally useful for formatting decimal numbers with customized patterns. This package and classes, help developers avoid writing complex code for textual representations and data formatting tasks.

Always start using a class from this package by importing it at the beginning of your Java program. Importing is done using the syntax:

• import java.text.DecimalFormat;
• This brings the DecimalFormat class into your program

number formatting

Number formatting in Java is an essential concept for applications that need to present numerical data in a human-readable format, especially when dealing with internationalization. Formatting numbers helps display them with appropriate separators, digit groupings, and decimal points.

Java makes this task manageable with the DecimalFormat class. Depending on the pattern provided, it can transform raw numerical data into a clean, formatted string. For instance, to display large numbers with commas every three digits and ensure two decimal places, a pattern like "#,##0.00" would be chosen.

Key elements used in formatting patterns are:

• # - Denotes an optional digit
• 0 - Represents a mandatory digit
• , - Used for grouping thousands
• . - Marks the decimal point

Java programming

Java is a versatile and widely used programming language largely because of its simplicity and portability. Java applications range from client-server space to web applications, and because of its platform-independent nature, it enjoys a broad utility spectrum across different industries.

As a Java programmer, it's crucial to grasp not only the language syntax but also the powerful libraries that Java offers, including the 'java.text' package for number and text formatting. Such an understanding allows you to create applications that are both efficient and user-friendly.

In day-to-day programming, Java’s flexibility shines through its object-oriented principles, like using classes and objects, which foster code reusability and encapsulation.

• Classes and objects help manage application logic
• Java's API is vast, providing readymade solutions to many common problems

DecimalFormat object

The DecimalFormat object in Java is an efficient tool when it comes to formatting numbers to strings according to specified patterns. With the DecimalFormat class, developers can define patterns that dictate how numbers should be displayed.

To create a DecimalFormat object, you instantiate it with a desired format pattern. For example, new DecimalFormat("#,##0.00") initializes an object that will format numbers with commas every three digits and two decimal places.

Using the format() method of this object, you can convert a double or other numeric types to a formatted string. This is especially useful in scenarios where the presentation of data is critical, such as in financial applications.

• This method handles rounding to the nearest decimal as needed
• It also ensures data is presented with numeric patterns that improve readability