Imagine you are managing payroll for a company and need to process a list of employee salaries. Your goal is to identify all employees earning above a certain threshold, give those employees a 10% raise, and then calculate the total cost of these increased salaries. Using Java's **Stream API** and **lambda expressions** can make this task concise and expressive, allowing you to filter, transform, and aggregate data efficiently in a single pipeline.

package com.example;

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import static org.junit.jupiter.api.Assertions.*;

public class MainTest {
    @Test
    @DisplayName("Returns correct sum for mixed salaries")
    void testMixedSalaries() {
        List<Integer> salaries = Arrays.asList(3200, 4500, 2100, 5000, 3800, 1900);
        int expected = (int) Math.round(3200 * 1.10) + (int) Math.round(4500 * 1.10) + (int) Math.round(5000 * 1.10) + (int) Math.round(3800 * 1.10);
        int actual = Main.processSalaries(salaries);
        assertEquals(expected, actual, "Should sum 10% increased salaries above 3000");
    }

    @Test
    @DisplayName("Filters out salaries at or below threshold")
    void testThresholdFiltering() {
        List<Integer> salaries = Arrays.asList(3000, 2999, 2500, 1000);
        int actual = Main.processSalaries(salaries);
        assertEquals(0, actual, "Should return 0 when all salaries are at or below threshold");
    }

    @Test
    @DisplayName("Rounds increased salaries correctly")
    void testRounding() {
        List<Integer> salaries = Arrays.asList(3051); // 3051*1.10 = 3356.1 -> 3356
        int expected = (int) Math.round(3051 * 1.10);
        int actual = Main.processSalaries(salaries);
        assertEquals(expected, actual, "Should round to nearest integer");
    }

    @Test
    @DisplayName("Returns 0 for empty list")
    void testEmptyList() {
        List<Integer> salaries = Collections.emptyList();
        int actual = Main.processSalaries(salaries);
        assertEquals(0, actual, "Should return 0 for empty list");
    }

    @Test
    @DisplayName("Returns 0 when no salaries above threshold")
    void testNoSalariesAboveThreshold() {
        List<Integer> salaries = Arrays.asList(1000, 2000, 3000);
        int actual = Main.processSalaries(salaries);
        assertEquals(0, actual, "Should return 0 when no salaries above threshold");
    }
}


MainTest.java

Master the power of lambda expressions in Java to write concise, expressive, and modern code. This course guides you from the basics of functional interfaces to advanced lambda usage, including real-world applications and best practices.

Learn the fundamentals of lambda expressions, their syntax, and how they fit into Java's type system.

Dive deeper into lambda expressions with method references, composition, and practical applications in collections.

Learn how to write clean, efficient, and maintainable code with lambda expressions in real-world scenarios.

Challenge: Stream Data Processing

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