What causes "This is a utility class and cannot be instantiated." in TheAlgorithms/Java?

Do not instantiate Average — call its static methods directly (Average.average(arr), Average.averageStream(arr)).

TheAlgorithms/Java · error · UnsupportedOperationException

This is a utility class and cannot be instantiated.

Error message

This is a utility class and cannot be instantiated.

What it means

Thrown by the private constructor of the Average utility class when an attempt is made to instantiate it. Average is a final class containing only static methods; the constructor deliberately throws UnsupportedOperationException to enforce the utility-class pattern. The JVM prevents external instantiation via the private modifier, but reflection or an internal subclass (not possible since the class is final) could theoretically trigger this.

Solutions

Do not instantiate Average — call its static methods directly (Average.average(arr), Average.averageStream(arr)).
If a reflection framework is auto-instantiating, exclude utility classes or annotate them to be skipped.
If scanning code is the culprit, filter out classes with only static methods or private constructors before attempting instantiation.

Example fix

// before (reflection triggers the exception)
Average avg = Average.class.getDeclaredConstructor().setAccessible(true).newInstance();

// after (use static methods — never instantiate)
double mean = Average.average(new double[]{1.0, 2.0, 3.0});

Defensive patterns

Strategy: type-guard

Validate before calling

// Never instantiate Average — use static methods directly
double mean = Average.average(new double[]{1.0, 2.0, 3.0});
// If using a reflection framework, skip classes with private constructors:
if (clazz == Average.class) continue; // skip utility class

Type guard

// Check whether a class should be instantiated (utility-class guard)
static boolean isInstantiable(Class<?> clazz) {
    try {
        Constructor<?> c = clazz.getDeclaredConstructor();
        return java.lang.reflect.Modifier.isPublic(c.getModifiers());
    } catch (NoSuchMethodException e) {
        return false;
    }
}

Try / catch

// If reflectively scanning packages, catch and skip utility classes
try {
    Object instance = clazz.getDeclaredConstructor().newInstance();
} catch (UnsupportedOperationException e) {
    // Skip utility classes that refuse instantiation
    continue;
}

Prevention

Always call Average methods statically — never use reflection to instantiate utility classes.
If a DI or scanning framework auto-instantiates classes, exclude or annotate utility classes.
Add a filter for classes with private constructors or no public constructor before reflection-based instantiation.

When it happens

Trigger: Attempting to instantiate Average via reflection: Average.class.getDeclaredConstructor().setAccessible(true).newInstance(). Calling new Average() directly fails at compile time due to the private constructor, so this only manifests at runtime through reflection.

Common situations: A reflection-based framework (dependency injection, serialization library, ORM) that auto-discovers and instantiates classes by scanning packages or annotations. A test utility that tries to instantiate all classes in a package for coverage analysis. A generic factory that reflectively creates instances of any class it encounters.

Related errors

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/291a31cb67353595. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/com/thealgorithms/maths/Average.java:19

package com.thealgorithms.maths;

import java.util.Arrays;
import java.util.OptionalDouble;

/**
 * A utility class for computing the average of numeric arrays.
 *
 * <p>This class provides static methods to calculate the arithmetic mean
 * of arrays of both {@code double} and {@code int} values. It also offers
 * a Stream-based alternative for modern, declarative usage.
 *
 * <p>All methods guard against {@code null} or empty inputs.
 */
public final class Average {

    // Prevent instantiation of this utility class
    private Average() {
        throw new UnsupportedOperationException("This is a utility class and cannot be instantiated.");
    }

    /**
     * Computes the arithmetic mean of a {@code double} array.
     *
     * <p>The average is calculated as the sum of all elements divided
     * by the number of elements: {@code avg = Σ(numbers[i]) / n}.
     *
     * @param numbers a non-null, non-empty array of {@code double} values
     * @return the arithmetic mean of the given numbers
     * @throws IllegalArgumentException if {@code numbers} is {@code null} or empty
     */
    public static double average(double[] numbers) {
        if (numbers == null || numbers.length == 0) {
            throw new IllegalArgumentException("Numbers array cannot be empty or null");
        }
        double sum = 0;
        for (double number : numbers) {

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