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

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

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

Challenge: Stream Data Processing

Lösung

Challenge: Stream Data Processing

Lösung