In this challenge, you will reinforce your understanding of **type conversion** by safely converting a `double` value to an `int`. Type conversion, especially from a floating-point type like `double` to an integral type like `int`, can result in **data loss** if the `double` contains a fractional part. It is important to alert users when such a loss occurs, so that they are aware of any unintended consequences of the conversion.

package com.example;

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

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;

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

public class MainTest {
    @Test
    @DisplayName("safeDoubleToInt prints warning and correct values for fractional double")
    void testSafeDoubleToIntWithFractional() {
        ByteArrayOutputStream outContent = new ByteArrayOutputStream();
        PrintStream originalOut = System.out;
        System.setOut(new PrintStream(outContent));

        Main.safeDoubleToInt(42.7);

        System.setOut(originalOut);
        String output = outContent.toString();
        String[] lines = output.split("\\r?\\n");
        assertTrue(lines.length >= 3, "Expected at least 3 lines of output, got: " + lines.length);
        assertEquals("Original double value: 42.7", lines[0].trim(), "First line should show original double value");
        assertEquals("Converted int value: 42", lines[1].trim(), "Second line should show converted int value");
        assertEquals("Warning: Data loss occurred during conversion.", lines[2].trim(), "Should print warning for data loss");
    }

    @Test
    @DisplayName("safeDoubleToInt prints correct values and no warning for whole number double")
    void testSafeDoubleToIntWithWholeNumber() {
        ByteArrayOutputStream outContent = new ByteArrayOutputStream();
        PrintStream originalOut = System.out;
        System.setOut(new PrintStream(outContent));

        Main.safeDoubleToInt(100.0);

        System.setOut(originalOut);
        String output = outContent.toString();
        String[] lines = output.split("\\r?\\n");
        assertTrue(lines.length >= 2, "Expected at least 2 lines of output, got: " + lines.length);
        assertEquals("Original double value: 100.0", lines[0].trim(), "First line should show original double value");
        assertEquals("Converted int value: 100", lines[1].trim(), "Second line should show converted int value");
        if (lines.length > 2) {
            for (int i = 2; i < lines.length; i++) {
                assertFalse(lines[i].trim().toLowerCase().contains("warning"), "Should not print warning for whole number");
            }
        }
    }
}


MainTest.java

A comprehensive course on Java data types, covering primitives, reference types, type conversion, and practical applications. Designed for learners with basic Java syntax knowledge.

Explore Java's built-in primitive data types, their properties, and how to use them effectively.

Delve into Java's reference types, focusing on Strings and arrays, and how they differ from primitives.

Learn about type casting, automatic conversions, and the use of wrapper classes for primitives.

Challenge: Safe Type Conversion

解答