Summary  
This chapter introduces Java’s primitive data types—byte, short, int, long, float, double, boolean, and char—explaining how to declare variables of each type and describing their memory usage and valid value ranges.

General domain of usage  
Coffee shop operations

Now that you know how to create variables, it's time to understand what kind of data you can put inside them. In Java, **primitive data types** are the most basic types of data we can store — they define what kind of information we are working with, whether that's numbers, true/false values, or single characters.


## Whole Number Types

Used when working with numbers that don't have decimals, like counts, totals, or quantities.

**`byte`** — for very small numbers, when you know the value will stay tiny:
```java
byte freeSamples = 12;
```

**`short`** — a bit bigger than `byte`, for small to medium numbers:
```java
short dailyCustomers = 850;
```

**`int`** — the most commonly used whole number type, the default choice for most situations:
```java
int monthlyOrders = 24500;
```

**`long`** — for very large numbers that go way beyond normal daily usage. Note the `L` suffix:
```java
long totalCoffeeBeansUsed = 5000000000L;
```

## Decimal Number Types

Used when we need precision, like pricing or measurements.

**`float`** — when we don't need very high precision. Note the `f` suffix:
```java
float coffeeTemperature = 22.5f;
```

**`double`** — the most commonly used decimal type, the default choice when working with money or prices:
```java
double lattePrice = 4.99;
```

## Boolean Type

`boolean` stores only two values — `true` or `false`. No "maybe", just a clear yes or no:
```java
boolean isCoffeeShopOpen = true;
```

## Character Type

`char` stores a single character — one letter, symbol, or number. Note the single quotes:
```java
char drinkSize = 'M';
```

-2⁻¹⁴⁹ to (2 - 2⁻²³) * 2¹²⁷

-2⁻¹⁰⁷⁴ to (2 - 2⁻⁵²) * 2¹⁰²³

package com.example;
import com.github.javaparser.StaticJavaParser;
import com.github.javaparser.ast.CompilationUnit;
import com.github.javaparser.ast.body.VariableDeclarator;
import com.github.javaparser.ast.expr.Expression;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.DynamicTest;
import org.junit.jupiter.api.TestFactory;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.PrintStream;
import java.util.Optional;
import java.util.stream.Stream;
import static org.junit.jupiter.api.Assertions.*;
import static org.junit.jupiter.api.DynamicTest.dynamicTest;

public class MainTest {
    private static CompilationUnit cu;

    @BeforeAll
    public static void setup() throws Exception {
        File projectRoot = new File(
            MainTest.class.getProtectionDomain().getCodeSource().getLocation().toURI()
        ).getParentFile().getParentFile();
        File file = new File(projectRoot, "src/main/java/com/example/Main.java");
        cu = StaticJavaParser.parse(file);
    }

    private String getVariableValue(String varName) {
        Optional<VariableDeclarator> var = cu.findAll(VariableDeclarator.class).stream()
                .filter(v -> v.getNameAsString().equals(varName))
                .findFirst();
        return var.flatMap(v -> v.getInitializer().map(Object::toString)).orElse(null);
    }

    @TestFactory
    Stream<DynamicTest> variableValueTests() {
        return Stream.of(
                new String[]{"firstNumber", "9"},
                new String[]{"secondNumber", "4"},
                new String[]{"thirdNumber", "2.0"}
        ).map(pair -> {
            String varName = pair[0];
            String expectedValue = pair[1];
            String actualValue = getVariableValue(varName);
            boolean passed = expectedValue.equals(actualValue);
            String displayName = passed ?
                    varName + " has expected value: " + expectedValue :
                    "Expected " + varName + " = " + expectedValue + ", but got: " + actualValue;
            return dynamicTest(displayName, () -> assertEquals(expectedValue, actualValue));
        });
    }

    @TestFactory
    Stream<DynamicTest> outputTest() {
        return Stream.of(dynamicTest("Result value matches output", () -> {
            ByteArrayOutputStream outContent = new ByteArrayOutputStream();
            PrintStream originalOut = System.out;
            System.setOut(new PrintStream(outContent));
            Main.main(new String[]{});
            System.setOut(originalOut);
            String output = outContent.toString().trim();
            String expectedResult = "6.5";
            String testName = output.equals(expectedResult)
                    ? "result has correct value: " + expectedResult
                    : "Expected result = " + expectedResult + ", but got: " + output;
            assertEquals(expectedResult, output, testName);
        }));
    }

    @TestFactory
    Stream<DynamicTest> hardcodedExpressionCheck() {
        Optional<VariableDeclarator> resultVar = cu.findAll(VariableDeclarator.class).stream()
                .filter(v -> v.getNameAsString().equals("result"))
                .findFirst();
        String displayName;
        if (resultVar.isPresent()) {
            Expression init = resultVar.get().getInitializer().orElse(null);
            boolean usesVariables = init != null && init.toString().contains("firstNumber") && init.toString().contains("secondNumber");
            displayName = usesVariables
                    ? "result expression uses declared variables"
                    : "result expression uses hardcoded values (should use variables)";
            return Stream.of(dynamicTest(displayName, () -> assertTrue(usesVariables, "Detected hardcoded numbers in result expression: " + init)));
        }
        return Stream.of(dynamicTest("result variable not found", () -> fail("Variable 'result' not found")));
    }
}

MainTest.java

Dive into the fundamentals of Java by learning the core concepts that power modern applications. Explore variables, data types, operators, conditionals, and strings while building a strong foundation in programming. Through practical examples and hands-on challenges, you'll develop the skills needed to write, understand, and troubleshoot Java code with confidence.

Discover how to begin your Java journey by learning what Java is, where it is used, and how Java programs are structured. Understand how to print output, write comments, and build the foundation needed for all future programming concepts.

Master the skills needed to store, manage, and work with data in Java. Learn how variables, constants, data types, operators, and type casting work, and apply these concepts through practical coding exercises and real-world examples.

Explore the essentials of decision-making in Java by working with comparison and logical operators, conditional statements, and switch expressions. Learn how programs evaluate conditions, make choices, and respond to different situations through practical examples and challenges.

Dive into the fundamentals of working with text in Java. Learn how strings are created and manipulated, explore formatting and comparison techniques, validate user input, extract useful information from text, and apply these skills in realistic programming scenarios.

Primitive Data Types

Whole Number Types

Decimal Number Types

Boolean Type

Character Type

Solution