In this challenge, you will apply what you have learned about the `DecimalFormat` class to format both invoice numbers and monetary amounts for a list of invoices. Your goal is to produce output where each invoice appears as `"Invoice #XXXX: $X,XXX.XX"`, with the invoice number zero-padded to four digits and the amount formatted with grouping separators and exactly two decimal places. This task will help you practice combining number formatting patterns for both integers and floating-point values, and reinforce your understanding of grouping, padding, and currency display.

package com.example;

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;

import java.util.Arrays;
import java.util.List;
import java.util.regex.Pattern;

import static org.junit.jupiter.api.Assertions.*;

public class MainTest {

    @Test
    @DisplayName("Returns a list of strings with length equal to the input lists")
    void testListLength() {
        List<Integer> invoiceNumbers = Arrays.asList(10, 20, 30);
        List<Double> amounts = Arrays.asList(100.0, 200.0, 300.0);
        List<String> result = InvoiceFormatter.formatInvoices(invoiceNumbers, amounts);
        assertEquals(invoiceNumbers.size(), result.size(), "The returned list should have the same length as the input lists");
    }

    @Test
    @DisplayName("Each invoice number is formatted as a four-digit, zero-padded number")
    void testInvoiceNumberFormatting() {
        List<Integer> invoiceNumbers = Arrays.asList(1, 25, 123, 4567);
        List<Double> amounts = Arrays.asList(1.0, 1.0, 1.0, 1.0);
        List<String> result = InvoiceFormatter.formatInvoices(invoiceNumbers, amounts);
        assertTrue(result.get(0).contains("#0001"), "Invoice number 1 should be formatted as #0001");
        assertTrue(result.get(1).contains("#0025"), "Invoice number 25 should be formatted as #0025");
        assertTrue(result.get(2).contains("#0123"), "Invoice number 123 should be formatted as #0123");
        assertTrue(result.get(3).contains("#4567"), "Invoice number 4567 should be formatted as #4567");
    }

    @Test
    @DisplayName("Each amount is formatted with a dollar sign, grouping separators, and two decimal digits")
    void testAmountFormatting() {
        List<Integer> invoiceNumbers = Arrays.asList(1, 2, 3);
        List<Double> amounts = Arrays.asList(12.0, 1234.5, 1234567.89);
        List<String> result = InvoiceFormatter.formatInvoices(invoiceNumbers, amounts);
        assertTrue(result.get(0).matches(".*\\\$12.00$"), "Amount 12.0 should be formatted as $12.00");
        assertTrue(result.get(1).matches(".*\\\$1,234.50$"), "Amount 1234.5 should be formatted as $1,234.50");
        assertTrue(result.get(2).matches(".*\\\$1,234,567.89$"), "Amount 1234567.89 should be formatted as $1,234,567.89");
    }

    @Test
    @DisplayName("The output strings are in the format 'Invoice #XXXX: $X,XXX.XX'")
    void testFullStringFormat() {
        List<Integer> invoiceNumbers = Arrays.asList(42);
        List<Double> amounts = Arrays.asList(9876.54);
        List<String> result = InvoiceFormatter.formatInvoices(invoiceNumbers, amounts);
        Pattern pattern = Pattern.compile("^Invoice #\\\d{4}: \\\$[\\\d,]+\\\.\\\d{2}$");
        assertTrue(pattern.matcher(result.get(0)).matches(), "Output should match the required format: 'Invoice #XXXX: $X,XXX.XX'");
    }

    @Test
    @DisplayName("Handles whole numbers and decimals in amounts")
    void testWholeAndDecimalAmounts() {
        List<Integer> invoiceNumbers = Arrays.asList(100, 200);
        List<Double> amounts = Arrays.asList(50.0, 75.25);
        List<String> result = InvoiceFormatter.formatInvoices(invoiceNumbers, amounts);
        assertTrue(result.get(0).endsWith("$50.00"), "Whole number amount should be formatted with two decimal places");
        assertTrue(result.get(1).endsWith("$75.25"), "Decimal amount should be formatted with two decimal places");
    }
}


MainTest.java

Master the art of formatting and parsing data in Java, from string templates to numbers and dates, and learn how to create well-structured console tables. This course is designed for learners with a basic understanding of Java syntax who want to deepen their skills in data presentation and manipulation.

Explore the power of String.format() for dynamic and readable string construction in Java, including formatting numbers, aligning text, and embedding variables.

Delve into the DecimalFormat class for precise control over numeric output, including custom patterns, rounding, and parsing.

Master date parsing/formatting with LocalDate and DateTimeFormatter, and learn to create visually appealing tables in the console.

Challenge: Invoice Number Formatter

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Challenge: Invoice Number Formatter

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