Add Java code optimization demo with Gradle and JUnit 4/5 (#2369)

## Summary
Added Java code optimization demonstration project to
`cli/code-to-optimize/`

- Set up Gradle build system with dual JUnit support (JUnit 4 and JUnit
5)
- Created three classes with common optimization opportunities:
- **StringProcessor**: String concatenation and manipulation
inefficiencies
- **CollectionProcessor**: Collection operations with performance issues
  - **DataCalculator**: Algorithm optimization opportunities
- Added comprehensive test suite with 20+ tests
- All tests passing with `./gradlew test`

## Code Optimization Opportunities

### StringProcessor
- String concatenation in loops (O(n²) → O(n) with StringBuilder)
- Multiple intermediate String objects
- Repeated substring operations

### CollectionProcessor
- ArrayList.contains() lookups (O(n²) → O(n) with HashSet)
- Multiple collection passes (can be single pass)
- Inefficient recursive implementations

### DataCalculator
- Fibonacci without memoization (O(2ⁿ) → O(n) with DP)
- Prime checking inefficiency (O(n) → O(√n))
- Simple power modulo (can use fast exponentiation)

## Project Structure
```
cli/code-to-optimize/
├── build.gradle (JUnit 4 & 5 configured)
├── settings.gradle
├── README.md
├── gradlew (executable)
├── gradle/wrapper/
└── src/
    ├── main/java/com/example/optimization/
    │   ├── StringProcessor.java
    │   ├── CollectionProcessor.java
    │   └── DataCalculator.java
    └── test/java/com/example/optimization/
        ├── StringProcessorTest.java (JUnit 5)
        ├── CollectionProcessorTest.java (JUnit 4)
        └── DataCalculatorTest.java (JUnit 5)
```

## Test Coverage
- JUnit 5 tests for StringProcessor and DataCalculator (with
parameterized tests)
- JUnit 4 tests for CollectionProcessor
- Both frameworks working together via JUnit Vintage Engine
- 20+ test cases covering all optimization scenarios

## Running Tests
```bash
cd cli/code-to-optimize
./gradlew test      # Run all tests
./gradlew build     # Build the project
```

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Ubuntu <ubuntu@ip-172-31-39-200.ec2.internal>
Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

cli/code-to-optimize/build.gradle

@@ -0,0 +1,32 @@
+plugins {
+    id 'java'
+}
+
+group = 'com.example'
+version = '1.0-SNAPSHOT'
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    // JUnit 5 (Jupiter)
+    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.10.1'
+    testImplementation 'org.junit.jupiter:junit-jupiter-params:5.10.1'
+    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.10.1'
+
+    // JUnit 4
+    testImplementation 'junit:junit:4.13.2'
+
+    // JUnit Vintage to run JUnit 4 tests with JUnit 5
+    testRuntimeOnly 'org.junit.vintage:junit-vintage-engine:5.10.1'
+}
+
+test {
+    useJUnitPlatform()
+}
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_11
+    targetCompatibility = JavaVersion.VERSION_11
+}

cli/code-to-optimize/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.5-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

cli/code-to-optimize/gradlew

@@ -0,0 +1,189 @@
+#!/bin/sh
+
+##############################################################################
+# Gradle start up script for UN*X
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+# This is normally unused
+# shellcheck disable=SC2034
+APP_BASE_NAME=${0##*/}
+APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    if ! command -v java >/dev/null 2>&1
+    then
+        die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC3045
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC3045
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+    die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"

cli/code-to-optimize/settings.gradle

@@ -0,0 +1 @@
+rootProject.name = 'code-optimization-demo'

cli/code-to-optimize/src/main/java/com/example/optimization/CollectionProcessor.java

@@ -0,0 +1,66 @@
+package com.example.optimization;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Collection processing class with inefficient implementations
+ * that need optimization.
+ */
+public class CollectionProcessor {
+
+    /**
+     * Inefficient: Uses contains() which is O(n) for ArrayList
+     * Should use HashSet for O(1) lookup
+     */
+    public List<Integer> removeDuplicates(List<Integer> numbers) {
+        List<Integer> result = new ArrayList<>();
+        for (Integer num : numbers) {
+            if (!result.contains(num)) {
+                result.add(num);
+            }
+        }
+        return result;
+    }
+
+    /**
+     * Inefficient: Multiple passes through the collection
+     * Should use a single pass with tracking variables
+     */
+    public int sumOfEvens(List<Integer> numbers) {
+        List<Integer> evens = new ArrayList<>();
+        for (Integer num : numbers) {
+            if (num % 2 == 0) {
+                evens.add(num);
+            }
+        }
+
+        int sum = 0;
+        for (Integer num : evens) {
+            sum += num;
+        }
+        return sum;
+    }
+
+    /**
+     * Inefficient: Creates new list on each recursive call
+     * Should use iterative approach or accumulator
+     */
+    public List<Integer> filterPositive(List<Integer> numbers) {
+        if (numbers.isEmpty()) {
+            return new ArrayList<>();
+        }
+
+        List<Integer> result = new ArrayList<>();
+        Integer first = numbers.get(0);
+
+        if (first > 0) {
+            result.add(first);
+        }
+
+        List<Integer> rest = numbers.subList(1, numbers.size());
+        result.addAll(filterPositive(rest));
+
+        return result;
+    }
+}

cli/code-to-optimize/src/main/java/com/example/optimization/DataCalculator.java

@@ -0,0 +1,47 @@
+package com.example.optimization;
+
+/**
+ * Data calculation class with inefficient implementations
+ * that need optimization.
+ */
+public class DataCalculator {
+
+    /**
+     * Inefficient: Recalculates Fibonacci values recursively without memoization
+     * Should use dynamic programming or iterative approach
+     */
+    public long fibonacci(int n) {
+        if (n <= 1) {
+            return n;
+        }
+        return fibonacci(n - 1) + fibonacci(n - 2);
+    }
+
+    /**
+     * Inefficient: Uses trial division for every number
+     * Should use Sieve of Eratosthenes for multiple primes
+     */
+    public boolean isPrime(int number) {
+        if (number <= 1) {
+            return false;
+        }
+        for (int i = 2; i < number; i++) {
+            if (number % i == 0) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /**
+     * Inefficient: Uses pow and division operations unnecessarily
+     * Should use modular arithmetic directly
+     */
+    public int powerModulo(int base, int exponent, int modulo) {
+        int result = 1;
+        for (int i = 0; i < exponent; i++) {
+            result = (result * base) % modulo;
+        }
+        return result;
+    }
+}

cli/code-to-optimize/src/main/java/com/example/optimization/StringProcessor.java

@@ -0,0 +1,52 @@
+package com.example.optimization;
+
+import java.util.List;
+
+/**
+ * String processing class with inefficient implementations
+ * that need optimization.
+ */
+public class StringProcessor {
+
+    /**
+     * Inefficient: Uses String concatenation in a loop
+     * Should use StringBuilder for better performance
+     */
+    public String concatenateStrings(List<String> strings) {
+        String result = "";
+        for (String str : strings) {
+            result += str + " ";
+        }
+        return result.trim();
+    }
+
+    /**
+     * Inefficient: Creates multiple intermediate String objects
+     * Should use StringBuilder or single replace chain
+     */
+    public String sanitizeInput(String input) {
+        String result = input;
+        result = result.replace("&", "&amp;");
+        result = result.replace("<", "&lt;");
+        result = result.replace(">", "&gt;");
+        result = result.replace("\"", "&quot;");
+        result = result.replace("'", "&#x27;");
+        return result;
+    }
+
+    /**
+     * Inefficient: Uses repeated substring operations
+     * Should use a single pass algorithm
+     */
+    public String reverseWords(String sentence) {
+        String[] words = sentence.split(" ");
+        String result = "";
+        for (int i = words.length - 1; i >= 0; i--) {
+            result += words[i];
+            if (i > 0) {
+                result += " ";
+            }
+        }
+        return result;
+    }
+}

cli/code-to-optimize/src/test/java/com/example/optimization/CollectionProcessorTest.java

@@ -0,0 +1,71 @@
+package com.example.optimization;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.Assert.*;
+
+/**
+ * JUnit 4 tests for CollectionProcessor
+ */
+public class CollectionProcessorTest {
+
+    private CollectionProcessor processor;
+
+    @Before
+    public void setUp() {
+        processor = new CollectionProcessor();
+    }
+
+    @Test
+    public void testRemoveDuplicates() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 2, 4, 3, 5);
+        List<Integer> result = processor.removeDuplicates(numbers);
+        assertEquals(Arrays.asList(1, 2, 3, 4, 5), result);
+    }
+
+    @Test
+    public void testRemoveDuplicatesEmptyList() {
+        List<Integer> numbers = Arrays.asList();
+        List<Integer> result = processor.removeDuplicates(numbers);
+        assertTrue(result.isEmpty());
+    }
+
+    @Test
+    public void testSumOfEvens() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        int result = processor.sumOfEvens(numbers);
+        assertEquals(12, result); // 2 + 4 + 6 = 12
+    }
+
+    @Test
+    public void testSumOfEvensNoEvens() {
+        List<Integer> numbers = Arrays.asList(1, 3, 5, 7);
+        int result = processor.sumOfEvens(numbers);
+        assertEquals(0, result);
+    }
+
+    @Test
+    public void testFilterPositive() {
+        List<Integer> numbers = Arrays.asList(-2, 3, -1, 5, 0, 7);
+        List<Integer> result = processor.filterPositive(numbers);
+        assertEquals(Arrays.asList(3, 5, 7), result);
+    }
+
+    @Test
+    public void testFilterPositiveAllNegative() {
+        List<Integer> numbers = Arrays.asList(-1, -2, -3);
+        List<Integer> result = processor.filterPositive(numbers);
+        assertTrue(result.isEmpty());
+    }
+
+    @Test
+    public void testFilterPositiveAllPositive() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3);
+        List<Integer> result = processor.filterPositive(numbers);
+        assertEquals(Arrays.asList(1, 2, 3), result);
+    }
+}

cli/code-to-optimize/src/test/java/com/example/optimization/DataCalculatorTest.java

@@ -0,0 +1,93 @@
+package com.example.optimization;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * JUnit 5 tests for DataCalculator
+ */
+@DisplayName("DataCalculator Tests (JUnit 5)")
+class DataCalculatorTest {
+
+    private DataCalculator calculator;
+
+    @BeforeEach
+    void setUp() {
+        calculator = new DataCalculator();
+    }
+
+    @Test
+    @DisplayName("Should calculate Fibonacci for n=0")
+    void testFibonacciZero() {
+        assertEquals(0, calculator.fibonacci(0));
+    }
+
+    @Test
+    @DisplayName("Should calculate Fibonacci for n=1")
+    void testFibonacciOne() {
+        assertEquals(1, calculator.fibonacci(1));
+    }
+
+    @ParameterizedTest
+    @DisplayName("Should calculate Fibonacci correctly")
+    @CsvSource({
+        "2, 1",
+        "3, 2",
+        "4, 3",
+        "5, 5",
+        "6, 8",
+        "7, 13",
+        "10, 55"
+    })
+    void testFibonacci(int n, long expected) {
+        assertEquals(expected, calculator.fibonacci(n));
+    }
+
+    @ParameterizedTest
+    @DisplayName("Should identify prime numbers correctly")
+    @CsvSource({
+        "2, true",
+        "3, true",
+        "4, false",
+        "5, true",
+        "17, true",
+        "20, false",
+        "23, true",
+        "100, false"
+    })
+    void testIsPrime(int number, boolean expected) {
+        assertEquals(expected, calculator.isPrime(number));
+    }
+
+    @Test
+    @DisplayName("Should return false for negative numbers")
+    void testIsPrimeNegative() {
+        assertFalse(calculator.isPrime(-5));
+    }
+
+    @Test
+    @DisplayName("Should return false for 0 and 1")
+    void testIsPrimeZeroAndOne() {
+        assertFalse(calculator.isPrime(0));
+        assertFalse(calculator.isPrime(1));
+    }
+
+    @Test
+    @DisplayName("Should calculate power modulo correctly")
+    void testPowerModulo() {
+        assertEquals(4, calculator.powerModulo(2, 2, 5)); // 2^2 % 5 = 4
+        assertEquals(1, calculator.powerModulo(3, 4, 10)); // 3^4 % 10 = 81 % 10 = 1
+        assertEquals(0, calculator.powerModulo(5, 3, 5)); // 5^3 % 5 = 0
+    }
+
+    @Test
+    @DisplayName("Should handle exponent 0")
+    void testPowerModuloZeroExponent() {
+        assertEquals(1, calculator.powerModulo(5, 0, 7)); // Any number^0 = 1
+    }
+}

cli/code-to-optimize/src/test/java/com/example/optimization/StringProcessorTest.java

@@ -0,0 +1,74 @@
+package com.example.optimization;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.DisplayName;
+
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * JUnit 5 tests for StringProcessor
+ */
+@DisplayName("StringProcessor Tests (JUnit 5)")
+class StringProcessorTest {
+
+    private StringProcessor processor;
+
+    @BeforeEach
+    void setUp() {
+        processor = new StringProcessor();
+    }
+
+    @Test
+    @DisplayName("Should concatenate strings correctly")
+    void testConcatenateStrings() {
+        List<String> strings = Arrays.asList("Hello", "World", "Java");
+        String result = processor.concatenateStrings(strings);
+        assertEquals("Hello World Java", result);
+    }
+
+    @Test
+    @DisplayName("Should handle empty list")
+    void testConcatenateEmptyList() {
+        List<String> strings = Arrays.asList();
+        String result = processor.concatenateStrings(strings);
+        assertEquals("", result);
+    }
+
+    @Test
+    @DisplayName("Should sanitize HTML special characters")
+    void testSanitizeInput() {
+        String input = "<script>alert('XSS')</script>";
+        String result = processor.sanitizeInput(input);
+        assertEquals("&lt;script&gt;alert(&#x27;XSS&#x27;)&lt;/script&gt;", result);
+    }
+
+    @Test
+    @DisplayName("Should handle input with quotes")
+    void testSanitizeQuotes() {
+        String input = "He said \"Hello\" & 'Goodbye'";
+        String result = processor.sanitizeInput(input);
+        assertTrue(result.contains("&quot;"));
+        assertTrue(result.contains("&#x27;"));
+        assertTrue(result.contains("&amp;"));
+    }
+
+    @Test
+    @DisplayName("Should reverse words in sentence")
+    void testReverseWords() {
+        String sentence = "Hello World Java";
+        String result = processor.reverseWords(sentence);
+        assertEquals("Java World Hello", result);
+    }
+
+    @Test
+    @DisplayName("Should handle single word")
+    void testReverseSingleWord() {
+        String sentence = "Hello";
+        String result = processor.reverseWords(sentence);
+        assertEquals("Hello", result);
+    }
+}