Conformed to Java conventions and updated all directories of Chapter 4.

src/main/java/chapter04/multiplication/Multiplier.java

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+// Code written as part of the Java-Methods-Program-AP-Comp-A-2021-2022 repository on GitHub.
+package chapter04.multiplication;
+
+/**
+ * A class that provides an iterative addition implementation (i.e., multiplication).
+ */
+public class Multiplier {
+    /**
+     * Multiplies two numbers by iterative addition.
+     * <p>
+     * This method of multiplication restricts <i>b</i> to positive integers, since adding a number <i>n</i> times,
+     * where <i>n</i> is not a natural number, does not make sense. Theoretically, <i>a</i> could be any real number,
+     * however for simplicity's sake, <i>a</i> is made to be an integer.
+     *
+     * @param a Any integer.
+     * @param b Any positive integer.
+     * @return The product of <i>a</i> and <i>b</i>. If <i>b</i> is negative, returns {@code 0}.
+     */
+    public static int product(int a, int b) {
+        int result = 0;
+        for (int counter = 0; counter < b; counter++) {
+            result = result + a; // Does not run if "counter < b" is impossible
+        }
+        return result;
+    }
+
+    public static void main(String[] args) {
+        System.out.println(product(10, 5));
+    }
+}

src/main/java/chapter04/multiplicationrecursive/RecursiveMultiplier.java

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+// Code written as part of the Java-Methods-Program-AP-Comp-A-2021-2022 repository on GitHub.
+package chapter04.multiplicationrecursive;
+
+/**
+ * A class that provides an iterative addition implementation by recursion.
+ */
+public class RecursiveMultiplier {
+    /**
+     * Multiplies two numbers by iterative addition using recursion.
+     * <p>
+     * This method of multiplication restricts <i>b</i> to positive integers. Again, <i>a</i> could be any real
+     * number, but is an integer for simplicity.
+     *
+     * @param a Any integer.
+     * @param b Any positive integer.
+     * @return The product of <i>a</i> and <i>b</i>.
+     * @throws StackOverflowError If a negative integer is passed to <i>b</i>. Because of the way this is implemented,
+     * passing a negative number to <i>b</i> runs the function and never reaches the base case (i.e., never satisfies
+     * the conditions needed to end recursion). Thus, the call stack's maximum allowed depth is reached with infinite
+     * recursion and the fatal {@link StackOverflowError} is thrown. This is a reason recursion should be used
+     * cautiously.
+     */
+    public static int product(int a, int b) {
+        if ((a == 0) || (b == 0)) { // StackOverflowError could be avoided if "b == 0" is changed to "b <= 0"
+            return 0;
+        } else {
+            return (a + product(a, b - 1));
+        }
+    }
+
+    public static void main(String[] args) {
+        System.out.println(product(10, 5));
+    }
+}

src/main/java/chapter04/printtriangle/TrianglePrinter.java

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+// Code written as part of the Java-Methods-Program-AP-Comp-A-2021-2022 repository on GitHub.
+package chapter04.printtriangle;
+
+/**
+ * A class that provides methods to print stars and triangles.
+ */
+public class TrianglePrinter {
+    /**
+     * Prints a given number of stars on the same line.
+     *
+     * @param stars The number of stars.
+     */
+    public static void printStars(int stars) {
+        for (int counter = 0; counter <= stars; counter++) {
+            System.out.print("*");
+        }
+    }
+
+    /**
+     * Prints a right triangle made of stars.
+     *
+     * @param lineNum The number of lines high the triangle is to be printed.
+     */
+    public static void printTriangle(int lineNum) {
+        for (int counter = 0; counter < lineNum; counter++) {
+            printStars(counter);
+            System.out.println();
+        }
+    }
+
+    public static void main(String[] args) {
+        printTriangle(5);
+    }
+}

src/main/java/chapter04/printtriangleinverse/InvertedTrianglePrinter.java

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+// Code written as part of the Java-Methods-Program-AP-Comp-A-2021-2022 repository on GitHub.
+package chapter04.printtriangleinverse;
+
+/**
+ * A class that provides a method to print an inverted triangle recursively.
+ */
+public class InvertedTrianglePrinter {
+    /**
+     * Prints an inverted right triangle made out of stars using recursion.
+     *
+     * @param stars The number of stars to be printed on the first line.
+     * @param display The current string. For a standard triangle, a string of {@code ""} should be passed, but
+     *                additional constant width can be added by passing in a string of asterisks.
+     */
+    public static void printTriangle(int stars, String display) {
+        if (stars <= 0) {
+            return;
+        }
+
+        display = display + "*";
+        printTriangle(stars - 1, display);
+        System.out.println(display);
+    }
+
+    public static void main(String[] args) {
+        String p = "";
+        printTriangle(5, p);
+    }
+}

src/main/java/chapter04/printtrianglerecursive/RecursiveTrianglePrinter.java

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+// Code written as part of the Java-Methods-Program-AP-Comp-A-2021-2022 repository on GitHub.
+package chapter04.printtrianglerecursive;
+
+/**
+ * A class that provides a method to print a triangle recursively.
+ */
+public class RecursiveTrianglePrinter {
+    /**
+     * Prints a right triangle made out of stars using recursion.
+     *
+     * @param stars The number of stars to be printed on the first line.
+     * @return The current string. This is not a useful value, it's only used for passing values back from recursion.
+     */
+    public static String printTriangle(int stars) {
+        if (stars <= 0) {
+            return "";
+        }
+
+        String display = printTriangle(stars - 1);
+        display = display + "*";
+        System.out.println(display);
+
+        return display;
+    }
+
+    public static void main(String[] args) {
+        printTriangle(5);
+    }
+}