⚡️ Speed up method StringUtils.isNumeric by 390%

[codeflash-ai]

📄 390% (3.90x) speedup for StringUtils.isNumeric in rewrite-core/src/main/java/org/openrewrite/internal/StringUtils.java

⏱️ Runtime : 2.26 milliseconds → 461 microseconds (best of 129 runs)

📝 Explanation and details

The optimization added a fast-path that checks c >= '0' && c <= '9' before calling Character.isDigit(c), allowing ASCII digits (the overwhelmingly common case) to bypass the expensive Unicode classification logic. Line profiler data shows the original spent 50.6% of time in Character.isDigit, while the optimized version distributes that cost across cheaper comparison checks (25.2% each for charAt and the ASCII range test), reducing per-call overhead. Unicode digits (Arabic-Indic, fullwidth) still fall through to Character.isDigit, preserving correctness. The 389% speedup comes from avoiding Unicode table lookups for typical inputs.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 31 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	Coverage data not available

🌀 Click to see Generated Regression Tests

package org.openrewrite.internal;

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

import java.lang.reflect.Constructor;

import static org.junit.jupiter.api.Assertions.*;
import org.openrewrite.internal.StringUtils;

public class StringUtilsTest {
    private StringUtils instance;

    @BeforeEach
    void setUp() throws Exception {
        // StringUtils has a private constructor. Create an instance via reflection to satisfy the requirement.
        Constructor<StringUtils> ctor = StringUtils.class.getDeclaredConstructor();
        ctor.setAccessible(true);
        instance = ctor.newInstance();
    }

    @Test
    void testTypicalNumericString_ReturnsTrue() {
        StringUtils.isNumeric("123456");
    }

    @Test
    void testSingleDigit_ReturnsTrue() {
        StringUtils.isNumeric("7");
    }

    @Test
    void testLeadingZeros_ReturnsTrue() {
        StringUtils.isNumeric("00123");
    }

    @Test
    void testInstanceInvocation_AllDigits_ReturnsTrue() {
        // Call the static method via the instance to demonstrate the created instance is usable.
        instance.isNumeric("42");
    }

    @Test
    void testNullInput_ReturnsFalse() {
        StringUtils.isNumeric(null);
    }

    @Test
    void testEmptyString_ReturnsFalse() {
        StringUtils.isNumeric("");
    }

    @Test
    void testNegativeNumberWithMinusSign_ReturnsFalse() {
        StringUtils.isNumeric("-123");
    }

    @Test
    void testDecimalNumberWithDot_ReturnsFalse() {
        StringUtils.isNumeric("12.3");
    }

    @Test
    void testStringWithSpaces_ReturnsFalse() {
        StringUtils.isNumeric(" 123");
    }

    @Test
    void testNonDigitCharacters_ReturnsFalse() {
        StringUtils.isNumeric("12a34");
    }

    @Test
    void testStringWithNewlineCharacter_ReturnsFalse() {
        StringUtils.isNumeric("123\n456");
    }

    @Test
    void testUnicodeArabicIndicDigits_ReturnsTrue() {
        // Arabic-Indic digits U+0661 U+0662 U+0663 represent digits and Character.isDigit should recognize them
        String arabicIndic = "\u0661\u0662\u0663";
        StringUtils.isNumeric(arabicIndic);
    }

    @Test
    void testFullwidthDigits_ReturnsTrue() {
        // Fullwidth digits (e.g., '１','２','３') are recognized by Character.isDigit
        String fullwidth = "\uFF11\uFF12\uFF13"; // "１２３"
        StringUtils.isNumeric(fullwidth);
    }

    @Test
    void testLargeNumericString_PerformanceAndCorrectness() {
        // Create a large numeric string to exercise the loop and ensure correctness on large inputs.
        int length = 100_000;
        StringBuilder sb = new StringBuilder(length);
        for (int i = 0; i < length; i++) {
            sb.append('9');
        }
        String largeNumeric = sb.toString();

        StringUtils.isNumeric(largeNumeric);
    }

    @Test
    void testStringWithCommaThousandsSeparator_ReturnsFalse() {
        StringUtils.isNumeric("1,000");
    }
}

package org.openrewrite.internal;

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

import java.lang.reflect.Constructor;

import static org.junit.jupiter.api.Assertions.*;
import org.openrewrite.internal.StringUtils;

public class StringUtilsTest_2 {
    private StringUtils instance;

    @BeforeEach
    void setUp() throws Exception {
        // StringUtils has a private constructor; create an instance via reflection to satisfy the requirement.
        Constructor<StringUtils> ctor = StringUtils.class.getDeclaredConstructor();
        ctor.setAccessible(true);
        instance = ctor.newInstance();
    }

    @Test
    void testTypicalNumericString_ReturnsTrue() {
        StringUtils.isNumeric("12345");
    }

    @Test
    void testNumericWithLeadingZeros_ReturnsTrue() {
        StringUtils.isNumeric("00000123");
    }

    @Test
    void testSingleDigit_ReturnsTrue() {
        StringUtils.isNumeric("7");
    }

    @Test
    void testNullInput_ReturnsFalse() {
        StringUtils.isNumeric(null);
    }

    @Test
    void testEmptyString_ReturnsFalse() {
        StringUtils.isNumeric("");
    }

    @Test
    void testStringWithSpaces_ReturnsFalse() {
        StringUtils.isNumeric("123 456");
    }

    @Test
    void testStringWithSign_ReturnsFalse() {
        StringUtils.isNumeric("-123");
        // Keep single assertion per test as much as possible, but sign variants are closely related.
        StringUtils.isNumeric("+123");
    }

    @Test
    void testDecimalNumber_ReturnsFalse() {
        StringUtils.isNumeric("12.3");
    }

    @Test
    void testAlphanumeric_ReturnsFalse() {
        StringUtils.isNumeric("123abc");
    }

    @Test
    void testUnicodeDigits_ArabicIndic_ReturnsTrue() {
        // Arabic-Indic digits: U+0660 .. U+0669. Example: ١٢٣ (U+0661 U+0662 U+0663)
        String arabicIndicDigits = "\u0661\u0662\u0663";
        StringUtils.isNumeric(arabicIndicDigits);
    }

    @Test
    void testFullWidthDigits_ReturnsTrue() {
        // Fullwidth digits: U+FF10 .. U+FF19. Example: １２３ (U+FF11 U+FF12 U+FF13)
        String fullWidthDigits = "\uFF11\uFF12\uFF13";
        StringUtils.isNumeric(fullWidthDigits);
    }

    @Test
    void testStringWithLineBreaks_ReturnsFalse() {
        StringUtils.isNumeric("123\n456");
        StringUtils.isNumeric("123\r456");
    }

    @Test
    void testLargeNumericString_Performance_ReturnsTrue() {
        // Large but reasonable size to keep unit test fast.
        int length = 100_000;
        StringBuilder sb = new StringBuilder(length);
        for (int i = 0; i < length; i++) {
            sb.append('9');
        }
        String largeNumeric = sb.toString();
        StringUtils.isNumeric(largeNumeric);
    }

    @Test
    void testLargeNumericStringWithNonDigitAtEnd_ReturnsFalse() {
        int length = 100_000;
        StringBuilder sb = new StringBuilder(length + 1);
        for (int i = 0; i < length; i++) {
            sb.append('8');
        }
        sb.append('x'); // non-digit at the end
        String largeWithNonDigit = sb.toString();
        StringUtils.isNumeric(largeWithNonDigit);
    }
}

To edit these changes git checkout codeflash/optimize-StringUtils.isNumeric-mnn9kkuz and push.