GotoFinal/DynamicEnum.java Secret

## DynamicEnum.java
/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2017. Diorite (by Bartłomiej Mazur (aka GotoFinal))
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

import java.lang.StackWalker.Option;
import java.lang.StackWalker.StackFrame;
import java.lang.reflect.Constructor;
import java.lang.reflect.Executable;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.Set;
import java.util.function.Supplier;
import java.util.stream.Collectors;

/**
 * Base class for creating dynamic enums, new elements can be added to dynamic enums, but not removed/changed.
 *
 * @param <T>
 *         type of enum.
 */
@SuppressWarnings({"unchecked", "rawtypes"})
public abstract class DynamicEnum<T extends DynamicEnum<T>> implements Comparable<T> {
    private static final StackWalker walker =
            StackWalker.getInstance(Set.of(Option.RETAIN_CLASS_REFERENCE, Option.SHOW_HIDDEN_FRAMES, Option.SHOW_REFLECT_FRAMES));

    int    ordinal = - 1;
    String name    = "\0";
    private final transient Supplier<String> prettyName = new Supplier<String>() {
        private String value;

        @Override
        public String get() {
            if (this.value == null) {
                this.value = DynamicEnum.this.createPrettyName();
            }
            return this.value;
        }
    };

    @SuppressWarnings("StringEquality")
    final void validate() {
        if ((this.ordinal == - 1) || (this.name == "\0")) {
            throw new IllegalStateException("Unregistered enum element: " + this.getClass() + ", " + this.name + ", " + this.ordinal);
        }
    }

    protected DynamicEnum() {
        Class<T> enumType = this.getDeclaringClass0();
        DynamicEnumType<T> dynamicEnumType = DynamicEnumType.getDynamicEnumType(enumType);
        List<StackFrame> stackFrames = walker.walk(s -> s.skip(2).collect(Collectors.toList()));
        List<StackFrame> validStack = new ArrayList<>(2);
        boolean foundSpecial = false;
        for (StackFrame stackFrame : stackFrames) {
            if (foundSpecial) {
                validStack.add(stackFrame);
                if (validStack.size() == 2) {
                    break;
                }
            }
            if (stackFrame.getDeclaringClass().equals(DynamicEnum.class) && stackFrame.getMethodName().equals("$")) {
                foundSpecial = true;
            }
        }
        if (! foundSpecial) {
            for (StackFrame stackFrame : stackFrames) {
                validStack.add(stackFrame);
                if (validStack.size() == 2) {
                    break;
                }
            }
        }
        switch (ValueType.findType(validStack, enumType, this.getClass())) {
            case DYNAMIC:
            case DYNAMIC_EXTENDED:
                return;
            case NORMAL:
            case EXTENDED:
                this.ordinal = dynamicEnumType.counter++;
                int index = 0;
                for (Field field : enumType.getDeclaredFields()) {
                    if (Modifier.isStatic(field.getModifiers()) && Modifier.isFinal(field.getModifiers()) && (field.getType() == enumType)) {
                        if (index++ == this.ordinal) {
                            this.name = field.getName();
                            dynamicEnumType.addElement((T) this);
                            return;
                        }
                    }
                }
                throw new IllegalStateException("Can't find enum value declaration");
        }
    }

    protected static <T extends DynamicEnum<T>> T $(Object... arguments) {
        StackFrame stackOne = walker.walk(s -> s.skip(1).limit(1).findFirst()).orElseThrow(InternalError::new);
        if (! DynamicEnum.class.isAssignableFrom(stackOne.getDeclaringClass())) {
            throw new InternalError("This method should be used only to create new instances of enum values!");
        }
        try {
            return findMatchingConstructor((Class<T>) stackOne.getDeclaringClass(), arguments).newInstance(arguments);
        }
        catch (RuntimeException e) {
            if (e.getCause() instanceof InstantiationException) {
                throw new InternalError("Can't create enum instance, there was error in constructor!", e.getCause());
            }
            throw new InternalError("Exception when invoking constructor!", e);
        }
        catch (Exception e) {
            throw new InternalError("Can't create enum instance using default constructor, $() method works only for simple constructor usages", e);
        }
    }

    /**
     * Returns ordinal of this enum element.
     *
     * @return ordinal of this enum element.
     */
    public final int ordinal() {
        this.validate();
        return this.ordinal;
    }

    /**
     * Returns name of this enum element.
     *
     * @return name of this enum element.
     */
    public final String name() {
        this.validate();
        return this.name;
    }

    /**
     * Returns name of this enum element in PascalCase and removed underscores.
     *
     * @return pretty name of this enum element.
     */
    public final String prettyName() {
        return Objects.requireNonNull(this.prettyName.get());
    }

    private String createPrettyName() {
        String toLowerCase = this.name.toLowerCase();
        char[] charArray = toLowerCase.toCharArray();
        StringBuilder sb = new StringBuilder(toLowerCase.length()).append(Character.toUpperCase(charArray[0]));
        char last = '\0';
        for (int i = 1; i < charArray.length; i++) {
            char c = charArray[i];
            if (last == '_') {
                sb.append(Character.toUpperCase(c));
            }
            else if (c != '_') {
                sb.append(c);
            }
            last = c;
        }
        return sb.toString();
    }

    /**
     * Returns the Class object corresponding to this enum constant's enum type. Two enum constants e1 and  e2 are of the same enum type if and only if
     * e1.getDeclaringClass() == e2.getDeclaringClass(). (The value returned by this method may differ from the one returned by the {@link Object#getClass}
     * method for enum constants with constant-specific class bodies.)
     *
     * @return the Class object corresponding to this enum constant's enum type
     */
    public final Class<T> getDeclaringClass() {
        this.validate();
        return this.getDeclaringClass0();
    }

    private Class<T> getDeclaringClass0() {
        Class<?> clazz = this.getClass();
        Class<?> superClass = clazz.getSuperclass();
        return (superClass.getSuperclass() == DynamicEnum.class) ? (Class<T>) superClass : (Class<T>) clazz;
    }

    /**
     * Compares this enum with the specified object for order.  Returns a
     * negative integer, zero, or a positive integer as this object is less
     * than, equal to, or greater than the specified object.
     *
     * Enum constants are only comparable to other enum constants of the
     * same enum type.  The natural order implemented by this
     * method is the order in which the constants are declared.
     */
    @Override
    public final int compareTo(T o) {
        this.validate();
        DynamicEnum<T> self = this;
        if ((self.getClass() != ((DynamicEnum<?>) o).getClass()) && // optimization
            (self.getDeclaringClass() != ((DynamicEnum<?>) o).getDeclaringClass())) {
            throw new ClassCastException();
        }
        o.validate();
        return self.ordinal - o.ordinal;
    }

    /**
     * Returns the name of this enum constant, as contained in the
     * declaration.  This method may be overridden, though it typically
     * isn't necessary or desirable.  An enum type should override this
     * method when a more "programmer-friendly" string form exists.
     *
     * @return the name of this enum constant
     */
    public String toString() {
        this.validate();
        return this.name;
    }

    /**
     * Returns true if the specified object is equal to this
     * enum constant.
     *
     * @param other
     *         the object to be compared for equality with this object.
     *
     * @return true if the specified object is equal to this enum constant.
     */
    public final boolean equals(Object other) {
        this.validate();
        if (other instanceof DynamicEnum) {
            ((DynamicEnum) other).validate();
            return this == other;
        }
        else {
            return false;
        }
    }

    /**
     * Returns a hash code for this enum constant.
     *
     * @return a hash code for this enum constant.
     */
    public final int hashCode() {
        this.validate();
        return super.hashCode();
    }

    /**
     * Throws CloneNotSupportedException.  This guarantees that enums
     * are never cloned, which is necessary to preserve their "singleton"
     * status.
     *
     * @return (never returns)
     */
    @Override
    protected final Object clone() throws CloneNotSupportedException {
        throw new CloneNotSupportedException();
    }

    /**
     * enum classes cannot have finalize methods.
     */
    @Override
    protected final void finalize() {}

    /**
     * Returns array of values of given enum.
     *
     * @param enumType
     *         type of enum.
     * @param <T>
     *         type og enum.
     *
     * @return array of values of given enum.
     */
    public static <T extends DynamicEnum<T>> T[] values(Class<T> enumType) {
        return DynamicEnumType.getDynamicEnumType(enumType).values.clone();
    }

    /**
     * Adds new enum element to this dynamic enum.
     *
     * @param enumValue
     *         enum value.
     * @param name
     *         name of enum value.
     * @param <T>
     *         type of enum.
     *
     * @return ordinal value of enum.
     */
    public static <T extends DynamicEnum<T>> int addEnumElement(String name, T enumValue) {
        Class<T> enumValueClass = (Class<T>) enumValue.getClass();
        while (enumValueClass.getSuperclass() != DynamicEnum.class) {
            enumValueClass = (Class<T>) enumValueClass.getSuperclass();
        }
        DynamicEnumType<T> dynamicEnumType = DynamicEnumType.getDynamicEnumType(enumValueClass);
        dynamicEnumType.addElement(enumValue, name);
        return enumValue.ordinal;
    }

    /**
     * Returns the enum constant of the specified enum type with the
     * specified name.
     * The name must match exactly an identifier used
     * to declare an enum constant in this type.
     *
     * @param <T>
     *         The enum type whose constant is to be returned
     * @param enumType
     *         the {@code Class} object of the enum type from which to return a constant
     * @param name
     *         the name of the constant to return
     *
     * @return the enum constant of the specified enum type with the specified name
     *
     * @exception IllegalArgumentException
     *         if the specified enum type has no constant with the specified name, or the specified class object does not represent an enum type
     */
    public static <T extends DynamicEnum<T>> T valueOf(Class<T> enumType, String name) {
        T result = DynamicEnumType.getDynamicEnumType(enumType).elementsMap.get(name);
        if (result != null) {
            return result;
        }
        throw new IllegalArgumentException("No enum constant " + enumType.getCanonicalName() + "." + name);
    }

    /**
     * Returns the enum constant of the specified enum type with the specified ordinal.
     *
     * @param <T>
     *         The enum type whose constant is to be returned
     * @param enumType
     *         the {@code Class} object of the enum type from which to return a constant
     * @param ordinal
     *         the name of the constant to return
     *
     * @return the enum constant of the specified enum type with the specified ordinal
     *
     * @exception IllegalArgumentException
     *         if the specified enum type has no constant with the specified ordinal, or the specified class object does not represent an enum type
     */
    public static <T extends DynamicEnum<T>> T valueOf(Class<T> enumType, int ordinal) {
        T[] values = DynamicEnumType.getDynamicEnumType(enumType).values;
        if ((ordinal >= 0) && (ordinal < values.length)) {
            T result = values[ordinal];
            if (result != null) {
                return result;
            }
        }
        throw new IllegalArgumentException("No enum constant " + enumType.getCanonicalName() + "#" + ordinal);
    }

    private static <T> Constructor<T> findMatchingConstructor(Class<T> type, Object... values) throws NoSuchMethodException, IllegalStateException {
        return findMatchingExecutable((Constructor<T>[]) type.getDeclaredConstructors(), values);
    }

    private static <T> Constructor<T> findMatchingExecutable(Constructor<T>[] executables,
                                                             Object... values) throws NoSuchMethodException, IllegalStateException {
        if (values.length == 0) {
            for (Constructor<T> executable : executables) {
                if (executable.getParameterCount() == 0) {
                    return setAccessible(executable);
                }
            }
            throw new NoSuchMethodException("Can't find no-args constructor.");
        }
        Class<?>[] paramTypes = new Class<?>[values.length];
        for (int i = 0; i < values.length; i++) {
            Object value = values[i];
            paramTypes[i] = (value == null) ? null : value.getClass();
        }
        // try to find exact matching constructor, and add any just compatible to collection.
        int exactMatches = 0;
        Constructor<T> exact = null;
        Constructor<T> bestMatch = null;
        for (Constructor<T> executable : executables) {
            if (executable.getParameterCount() != values.length) {
                continue;
            }
            CompatibleExecutableResults compatibleConstructor = isCompatibleExecutable(executable, paramTypes);
            if (compatibleConstructor == CompatibleExecutableResults.EXACT) {
                if (exactMatches >= 1) {
                    throw new IllegalStateException("Ambiguous constructors found " + Arrays.toString(paramTypes));
                }
                exact = executable;
                exactMatches += 1;
            }
            if (compatibleConstructor != CompatibleExecutableResults.INVALID) {
                bestMatch = getMoreSpecialized(bestMatch, executable);
            }
        }
        if (bestMatch == null) {
            throw new NoSuchMethodException("Can't find matching constructor for: " + Arrays.toString(paramTypes));
        }
        if (exact != null) {
            if (! bestMatch.equals(exact)) {
                throw new IllegalStateException("Ambiguous constructors found " + Arrays.toString(paramTypes));
            }
            return setAccessible(exact);
        }
        return setAccessible(bestMatch);
    }

    private static <T> Constructor<T> setAccessible(Constructor<T> executable) {
        executable.setAccessible(true);
        return executable;
    }

    private static <T> Constructor<T> getMoreSpecialized(Constructor<T> a, Constructor<T> b) {
        if (a == null) {
            return b;
        }
        if (b == null) {
            return a;
        }
        Class<?>[] aTypes = a.getParameterTypes();
        Class<?>[] bTypes = b.getParameterTypes();
        int result = 0;
        for (int i = 0; i < aTypes.length; i++) {
            Class<?> aType = aTypes[i];
            Class<?> bType = bTypes[i];
            if (aType.equals(bType)) {
                continue;
            }
            // if aType is less specialized than bType
            if ((aType.isPrimitive() && ! bType.isPrimitive()) ||
                getWrapperClass(aType).isAssignableFrom(getWrapperClass(bType))) {
                // one of prev types was less specialized, javac fails to find such constructor, we should too
                if (result < 0) {
                    throw new IllegalStateException("Ambiguous constructors found for: " + Arrays.toString(aTypes) + " and " + Arrays.toString(bTypes));
                }
                result += 1;
            }
            else {
                if (result > 0) {
                    throw new IllegalStateException("Ambiguous constructors found for: " + Arrays.toString(aTypes) + " and " + Arrays.toString(bTypes));
                }
                result -= 1;
            }
        }
        if (result == 0) {
            throw new IllegalStateException("Ambiguous constructors found for: " + Arrays.toString(aTypes) + " and " + Arrays.toString(bTypes));
        }
        if (result < 0) {
            return a;
        }
        return b;
    }

    private static CompatibleExecutableResults isCompatibleExecutable(Executable constructor, Class<?>[] providedTypes) {
        Class<?>[] constructorParameterTypes = constructor.getParameterTypes();
        boolean compatible = true;
        CompatibleExecutableResults current = CompatibleExecutableResults.EXACT;
        for (int i = 0; i < constructorParameterTypes.length; i++) {
            Class<?> providedType = providedTypes[i];
            Class<?> parameterType = constructorParameterTypes[i];

            // null can't be used as primitive
            if ((providedType == null) && parameterType.isPrimitive()) {
                return CompatibleExecutableResults.INVALID;
            }

            // handle primitives correctly by using wrapped type as boolean.class.isAssignableFrom(Boolean.class) => false
            if ((providedType != null) && ! getWrapperClass(parameterType).isAssignableFrom(providedType)) {
                return CompatibleExecutableResults.INVALID;
            }

            if ((providedType == null) || parameterType.equals(providedType)) {
                continue; // sill exact match
            }
            current = CompatibleExecutableResults.COMPATIBLE;
        }
        return current;
    }

    private enum CompatibleExecutableResults {
        EXACT,
        COMPATIBLE,
        INVALID
    }

    private static Class<?> getWrapperClass(Class<?> clazz) {
        if (! clazz.isPrimitive()) {
            return clazz;
        }
        if (clazz == boolean.class) {
            return Boolean.class;
        }
        if (clazz == byte.class) {
            return Byte.class;
        }
        if (clazz == short.class) {
            return Short.class;
        }
        if (clazz == char.class) {
            return Character.class;
        }
        if (clazz == int.class) {
            return Integer.class;
        }
        if (clazz == long.class) {
            return Long.class;
        }
        if (clazz == float.class) {
            return Float.class;
        }
        if (clazz == double.class) {
            return Double.class;
        }
        throw new Error("Unknown primitive type?"); // not possible?
    }
}

## DynamicEnumTest.java
/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2017. Diorite (by Bartłomiej Mazur (aka GotoFinal))
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

import org.junit.Assert;
import org.junit.Test;

public class DynamicEnumTest
{
    @Test
    public void testEnum()
    {
        Assert.assertSame(EnumExample.A, EnumExample.values()[0]);
        Assert.assertSame(EnumExample.B, EnumExample.values()[1]);
        Assert.assertSame(EnumExample.C, EnumExample.values()[2]);
        Assert.assertSame(EnumExample.A, EnumExample.valueOf("A"));

        EnumExample d = new EnumExample();
        EnumExample e = new EnumExample() {};
        Assert.assertSame(3, EnumExample.addEnumElement("D", d));
        Assert.assertSame(4, EnumExample.addEnumElement("E", e));
        Assert.assertSame(d, EnumExample.values()[3]);
        Assert.assertSame(e, EnumExample.values()[4]);
        Assert.assertSame(e, EnumExample.valueOf("E"));


        // 0 -> A, 1 -> B, 2 -> C, 3 -> D, 4 -> E
        for (EnumExample enumExample : EnumExample.values())
        {
            System.out.println(enumExample.ordinal() + " -> " + enumExample.name());
        }
    }

    static class EnumExample extends DynamicEnum<EnumExample>
    {
        public static final EnumExample A = $();
        public static final EnumExample B = $();
        public static final EnumExample C = new EnumExample()
        {
            public int doSomething() {return 7;}
        };

        public int doSomething() {return 5;}

        public static EnumExample[] values() {return DynamicEnum.values(EnumExample.class);}

        public static EnumExample valueOf(String name) {return DynamicEnum.valueOf(EnumExample.class, name);}
    }
}

## DynamicEnumType.java
/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2017. Diorite (by Bartłomiej Mazur (aka GotoFinal))
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

import java.lang.reflect.Array;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

final class DynamicEnumType<T extends DynamicEnum<T>> {
    private static final Map<Class<?>, DynamicEnumType<?>> types = new ConcurrentHashMap<>(20);

    final Map<String, T> elementsMap = Collections.synchronizedMap(new HashMap<>(10, 0.1f));
    private final Class<T> type;
    T[] values;
    volatile int counter;

    @SuppressWarnings("unchecked")
    DynamicEnumType(Class<T> type) {
        this.type = type;
        this.values = (T[]) Array.newInstance(type, 0);
    }

    synchronized void addElement(T element, String name) {
        element.name = name;
        element.ordinal = this.counter++;
        this.addElement(element);
    }

    @SuppressWarnings("unchecked")
    synchronized void addElement(T element) {
        int oldLength = this.values.length;
        if (element.ordinal != oldLength) {
            throw new IllegalStateException("Expected enum element of id: " + oldLength + " but got: " + element.ordinal);
        }
        T[] newValues = (T[]) Array.newInstance(this.type, oldLength + 1);
        System.arraycopy(this.values, 0, newValues, 0, oldLength);
        newValues[oldLength] = element;
        element.ordinal = oldLength;
        this.values = newValues;
        this.elementsMap.put(element.name, element);
    }

    @SuppressWarnings("unchecked")
    static <T extends DynamicEnum<T>> DynamicEnumType<T> getDynamicEnumType(Class<T> type) {
        DynamicEnumType<T> enumType = (DynamicEnumType<T>) types.get(type);
        if (enumType != null) {
            return enumType;
        }
        enumType = new DynamicEnumType<>(type);
        types.putIfAbsent(type, enumType);
        return enumType;
    }
}

## SampleEnum.java
/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2017. Diorite (by Bartłomiej Mazur (aka GotoFinal))
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

public class SampleEnum extends DynamicEnum<SampleEnum>
{
    public static final SampleEnum A = $("heh");

    private final String someProperty;

    SampleEnum(String someProperty) {this.someProperty = someProperty;}

    public String getSomeProperty() {return this.someProperty;}

    public static SampleEnum[] values() {return DynamicEnum.values(SampleEnum.class);}

    public static SampleEnum valueOf(String name) {return DynamicEnum.valueOf(SampleEnum.class, name);}

}

## ValueType.java
/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2017. Diorite (by Bartłomiej Mazur (aka GotoFinal))
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

import java.lang.StackWalker.StackFrame;
import java.util.List;

enum ValueType
{
    NORMAL,
    EXTENDED,
    DYNAMIC,
    DYNAMIC_EXTENDED;

    static ValueType findType(List<StackFrame> frames, Class<?> enumType, Class<?> elementType)
    {
        StackFrame stackOne = frames.get(0);
        if (stackOne.getMethodName().equals("<clinit>") && (stackOne.getDeclaringClass() == enumType))
        {
            return ValueType.NORMAL;
        }
        if (frames.size() == 2)
        {
            StackFrame stackTwo = frames.get(1);
            if (stackOne.getMethodName().equals("<init>") && (stackOne.getDeclaringClass() == elementType) && stackTwo.getMethodName().equals("<clinit>") &&
                (stackTwo.getDeclaringClass() == enumType))
            {
                return ValueType.EXTENDED;
            }
        }
        if (stackOne.getDeclaringClass().isAnonymousClass() && stackOne.getMethodName().equals("<init>") && (stackOne.getDeclaringClass() == elementType))
        {
            return ValueType.DYNAMIC_EXTENDED;
        }
        return ValueType.DYNAMIC;
    }
}
	/*
	* The MIT License (MIT)
	*
	* Copyright (c) 2017. Diorite (by Bartłomiej Mazur (aka GotoFinal))
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in all
	* copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
	* SOFTWARE.
	*/

	import java.lang.StackWalker.Option;
	import java.lang.StackWalker.StackFrame;
	import java.lang.reflect.Constructor;
	import java.lang.reflect.Executable;
	import java.lang.reflect.Field;
	import java.lang.reflect.Modifier;
	import java.util.ArrayList;
	import java.util.Arrays;
	import java.util.List;
	import java.util.Objects;
	import java.util.Set;
	import java.util.function.Supplier;
	import java.util.stream.Collectors;

	/**
	* Base class for creating dynamic enums, new elements can be added to dynamic enums, but not removed/changed.
	*
	* @param <T>
	* type of enum.
	*/
	@SuppressWarnings({"unchecked", "rawtypes"})
	public abstract class DynamicEnum<T extends DynamicEnum<T>> implements Comparable<T> {
	private static final StackWalker walker =
	StackWalker.getInstance(Set.of(Option.RETAIN_CLASS_REFERENCE, Option.SHOW_HIDDEN_FRAMES, Option.SHOW_REFLECT_FRAMES));

	int ordinal = - 1;
	String name = "\0";
	private final transient Supplier<String> prettyName = new Supplier<String>() {
	private String value;

	@Override
	public String get() {
	if (this.value == null) {
	this.value = DynamicEnum.this.createPrettyName();
	}
	return this.value;
	}
	};

	@SuppressWarnings("StringEquality")
	final void validate() {
	if ((this.ordinal == - 1) \|\| (this.name == "\0")) {
	throw new IllegalStateException("Unregistered enum element: " + this.getClass() + ", " + this.name + ", " + this.ordinal);
	}
	}

	protected DynamicEnum() {
	Class<T> enumType = this.getDeclaringClass0();
	DynamicEnumType<T> dynamicEnumType = DynamicEnumType.getDynamicEnumType(enumType);
	List<StackFrame> stackFrames = walker.walk(s -> s.skip(2).collect(Collectors.toList()));
	List<StackFrame> validStack = new ArrayList<>(2);
	boolean foundSpecial = false;
	for (StackFrame stackFrame : stackFrames) {
	if (foundSpecial) {
	validStack.add(stackFrame);
	if (validStack.size() == 2) {
	break;
	}
	}
	if (stackFrame.getDeclaringClass().equals(DynamicEnum.class) && stackFrame.getMethodName().equals("$")) {
	foundSpecial = true;
	}
	}
	if (! foundSpecial) {
	for (StackFrame stackFrame : stackFrames) {
	validStack.add(stackFrame);
	if (validStack.size() == 2) {
	break;
	}
	}
	}
	switch (ValueType.findType(validStack, enumType, this.getClass())) {
	case DYNAMIC:
	case DYNAMIC_EXTENDED:
	return;
	case NORMAL:
	case EXTENDED:
	this.ordinal = dynamicEnumType.counter++;
	int index = 0;
	for (Field field : enumType.getDeclaredFields()) {
	if (Modifier.isStatic(field.getModifiers()) && Modifier.isFinal(field.getModifiers()) && (field.getType() == enumType)) {
	if (index++ == this.ordinal) {
	this.name = field.getName();
	dynamicEnumType.addElement((T) this);
	return;
	}
	}
	}
	throw new IllegalStateException("Can't find enum value declaration");
	}
	}

	protected static <T extends DynamicEnum<T>> T $(Object... arguments) {
	StackFrame stackOne = walker.walk(s -> s.skip(1).limit(1).findFirst()).orElseThrow(InternalError::new);
	if (! DynamicEnum.class.isAssignableFrom(stackOne.getDeclaringClass())) {
	throw new InternalError("This method should be used only to create new instances of enum values!");
	}
	try {
	return findMatchingConstructor((Class<T>) stackOne.getDeclaringClass(), arguments).newInstance(arguments);
	}
	catch (RuntimeException e) {
	if (e.getCause() instanceof InstantiationException) {
	throw new InternalError("Can't create enum instance, there was error in constructor!", e.getCause());
	}
	throw new InternalError("Exception when invoking constructor!", e);
	}
	catch (Exception e) {
	throw new InternalError("Can't create enum instance using default constructor, $() method works only for simple constructor usages", e);
	}
	}

	/**
	* Returns ordinal of this enum element.
	*
	* @return ordinal of this enum element.
	*/
	public final int ordinal() {
	this.validate();
	return this.ordinal;
	}

	/**
	* Returns name of this enum element.
	*
	* @return name of this enum element.
	*/
	public final String name() {
	this.validate();
	return this.name;
	}

	/**
	* Returns name of this enum element in PascalCase and removed underscores.
	*
	* @return pretty name of this enum element.
	*/
	public final String prettyName() {
	return Objects.requireNonNull(this.prettyName.get());
	}

	private String createPrettyName() {
	String toLowerCase = this.name.toLowerCase();
	char[] charArray = toLowerCase.toCharArray();
	StringBuilder sb = new StringBuilder(toLowerCase.length()).append(Character.toUpperCase(charArray[0]));
	char last = '\0';
	for (int i = 1; i < charArray.length; i++) {
	char c = charArray[i];
	if (last == '_') {
	sb.append(Character.toUpperCase(c));
	}
	else if (c != '_') {
	sb.append(c);
	}
	last = c;
	}
	return sb.toString();
	}

	/**
	* Returns the Class object corresponding to this enum constant's enum type. Two enum constants e1 and e2 are of the same enum type if and only if
	* e1.getDeclaringClass() == e2.getDeclaringClass(). (The value returned by this method may differ from the one returned by the {@link Object#getClass}
	* method for enum constants with constant-specific class bodies.)
	*
	* @return the Class object corresponding to this enum constant's enum type
	*/
	public final Class<T> getDeclaringClass() {
	this.validate();
	return this.getDeclaringClass0();
	}

	private Class<T> getDeclaringClass0() {
	Class<?> clazz = this.getClass();
	Class<?> superClass = clazz.getSuperclass();
	return (superClass.getSuperclass() == DynamicEnum.class) ? (Class<T>) superClass : (Class<T>) clazz;
	}

	/**
	* Compares this enum with the specified object for order. Returns a
	* negative integer, zero, or a positive integer as this object is less
	* than, equal to, or greater than the specified object.
	*
	* Enum constants are only comparable to other enum constants of the
	* same enum type. The natural order implemented by this
	* method is the order in which the constants are declared.
	*/
	@Override
	public final int compareTo(T o) {
	this.validate();
	DynamicEnum<T> self = this;
	if ((self.getClass() != ((DynamicEnum<?>) o).getClass()) && // optimization
	(self.getDeclaringClass() != ((DynamicEnum<?>) o).getDeclaringClass())) {
	throw new ClassCastException();
	}
	o.validate();
	return self.ordinal - o.ordinal;
	}

	/**
	* Returns the name of this enum constant, as contained in the
	* declaration. This method may be overridden, though it typically
	* isn't necessary or desirable. An enum type should override this
	* method when a more "programmer-friendly" string form exists.
	*
	* @return the name of this enum constant
	*/
	public String toString() {
	this.validate();
	return this.name;
	}

	/**
	* Returns true if the specified object is equal to this
	* enum constant.
	*
	* @param other
	* the object to be compared for equality with this object.
	*
	* @return true if the specified object is equal to this enum constant.
	*/
	public final boolean equals(Object other) {
	this.validate();
	if (other instanceof DynamicEnum) {
	((DynamicEnum) other).validate();
	return this == other;
	}
	else {
	return false;
	}
	}

	/**
	* Returns a hash code for this enum constant.
	*
	* @return a hash code for this enum constant.
	*/
	public final int hashCode() {
	this.validate();
	return super.hashCode();
	}

	/**
	* Throws CloneNotSupportedException. This guarantees that enums
	* are never cloned, which is necessary to preserve their "singleton"
	* status.
	*
	* @return (never returns)
	*/
	@Override
	protected final Object clone() throws CloneNotSupportedException {
	throw new CloneNotSupportedException();
	}

	/**
	* enum classes cannot have finalize methods.
	*/
	@Override
	protected final void finalize() {}

	/**
	* Returns array of values of given enum.
	*
	* @param enumType
	* type of enum.
	* @param <T>
	* type og enum.
	*
	* @return array of values of given enum.
	*/
	public static <T extends DynamicEnum<T>> T[] values(Class<T> enumType) {
	return DynamicEnumType.getDynamicEnumType(enumType).values.clone();
	}

	/**
	* Adds new enum element to this dynamic enum.
	*
	* @param enumValue
	* enum value.
	* @param name
	* name of enum value.
	* @param <T>
	* type of enum.
	*
	* @return ordinal value of enum.
	*/
	public static <T extends DynamicEnum<T>> int addEnumElement(String name, T enumValue) {
	Class<T> enumValueClass = (Class<T>) enumValue.getClass();
	while (enumValueClass.getSuperclass() != DynamicEnum.class) {
	enumValueClass = (Class<T>) enumValueClass.getSuperclass();
	}
	DynamicEnumType<T> dynamicEnumType = DynamicEnumType.getDynamicEnumType(enumValueClass);
	dynamicEnumType.addElement(enumValue, name);
	return enumValue.ordinal;
	}

	/**
	* Returns the enum constant of the specified enum type with the
	* specified name.
	* The name must match exactly an identifier used
	* to declare an enum constant in this type.
	*
	* @param <T>
	* The enum type whose constant is to be returned
	* @param enumType
	* the {@code Class} object of the enum type from which to return a constant
	* @param name
	* the name of the constant to return
	*
	* @return the enum constant of the specified enum type with the specified name
	*
	* @exception IllegalArgumentException
	* if the specified enum type has no constant with the specified name, or the specified class object does not represent an enum type
	*/
	public static <T extends DynamicEnum<T>> T valueOf(Class<T> enumType, String name) {
	T result = DynamicEnumType.getDynamicEnumType(enumType).elementsMap.get(name);
	if (result != null) {
	return result;
	}
	throw new IllegalArgumentException("No enum constant " + enumType.getCanonicalName() + "." + name);
	}

	/**
	* Returns the enum constant of the specified enum type with the specified ordinal.
	*
	* @param <T>
	* The enum type whose constant is to be returned
	* @param enumType
	* the {@code Class} object of the enum type from which to return a constant
	* @param ordinal
	* the name of the constant to return
	*
	* @return the enum constant of the specified enum type with the specified ordinal
	*
	* @exception IllegalArgumentException
	* if the specified enum type has no constant with the specified ordinal, or the specified class object does not represent an enum type
	*/
	public static <T extends DynamicEnum<T>> T valueOf(Class<T> enumType, int ordinal) {
	T[] values = DynamicEnumType.getDynamicEnumType(enumType).values;
	if ((ordinal >= 0) && (ordinal < values.length)) {
	T result = values[ordinal];
	if (result != null) {
	return result;
	}
	}
	throw new IllegalArgumentException("No enum constant " + enumType.getCanonicalName() + "#" + ordinal);
	}

	private static <T> Constructor<T> findMatchingConstructor(Class<T> type, Object... values) throws NoSuchMethodException, IllegalStateException {
	return findMatchingExecutable((Constructor<T>[]) type.getDeclaredConstructors(), values);
	}

	private static <T> Constructor<T> findMatchingExecutable(Constructor<T>[] executables,
	Object... values) throws NoSuchMethodException, IllegalStateException {
	if (values.length == 0) {
	for (Constructor<T> executable : executables) {
	if (executable.getParameterCount() == 0) {
	return setAccessible(executable);
	}
	}
	throw new NoSuchMethodException("Can't find no-args constructor.");
	}
	Class<?>[] paramTypes = new Class<?>[values.length];
	for (int i = 0; i < values.length; i++) {
	Object value = values[i];
	paramTypes[i] = (value == null) ? null : value.getClass();
	}
	// try to find exact matching constructor, and add any just compatible to collection.
	int exactMatches = 0;
	Constructor<T> exact = null;
	Constructor<T> bestMatch = null;
	for (Constructor<T> executable : executables) {
	if (executable.getParameterCount() != values.length) {
	continue;
	}
	CompatibleExecutableResults compatibleConstructor = isCompatibleExecutable(executable, paramTypes);
	if (compatibleConstructor == CompatibleExecutableResults.EXACT) {
	if (exactMatches >= 1) {
	throw new IllegalStateException("Ambiguous constructors found " + Arrays.toString(paramTypes));
	}
	exact = executable;
	exactMatches += 1;
	}
	if (compatibleConstructor != CompatibleExecutableResults.INVALID) {
	bestMatch = getMoreSpecialized(bestMatch, executable);
	}
	}
	if (bestMatch == null) {
	throw new NoSuchMethodException("Can't find matching constructor for: " + Arrays.toString(paramTypes));
	}
	if (exact != null) {
	if (! bestMatch.equals(exact)) {
	throw new IllegalStateException("Ambiguous constructors found " + Arrays.toString(paramTypes));
	}
	return setAccessible(exact);
	}
	return setAccessible(bestMatch);
	}

	private static <T> Constructor<T> setAccessible(Constructor<T> executable) {
	executable.setAccessible(true);
	return executable;
	}

	private static <T> Constructor<T> getMoreSpecialized(Constructor<T> a, Constructor<T> b) {
	if (a == null) {
	return b;
	}
	if (b == null) {
	return a;
	}
	Class<?>[] aTypes = a.getParameterTypes();
	Class<?>[] bTypes = b.getParameterTypes();
	int result = 0;
	for (int i = 0; i < aTypes.length; i++) {
	Class<?> aType = aTypes[i];
	Class<?> bType = bTypes[i];
	if (aType.equals(bType)) {
	continue;
	}
	// if aType is less specialized than bType
	if ((aType.isPrimitive() && ! bType.isPrimitive()) \|\|
	getWrapperClass(aType).isAssignableFrom(getWrapperClass(bType))) {
	// one of prev types was less specialized, javac fails to find such constructor, we should too
	if (result < 0) {
	throw new IllegalStateException("Ambiguous constructors found for: " + Arrays.toString(aTypes) + " and " + Arrays.toString(bTypes));
	}
	result += 1;
	}
	else {
	if (result > 0) {
	throw new IllegalStateException("Ambiguous constructors found for: " + Arrays.toString(aTypes) + " and " + Arrays.toString(bTypes));
	}
	result -= 1;
	}
	}
	if (result == 0) {
	throw new IllegalStateException("Ambiguous constructors found for: " + Arrays.toString(aTypes) + " and " + Arrays.toString(bTypes));
	}
	if (result < 0) {
	return a;
	}
	return b;
	}

	private static CompatibleExecutableResults isCompatibleExecutable(Executable constructor, Class<?>[] providedTypes) {
	Class<?>[] constructorParameterTypes = constructor.getParameterTypes();
	boolean compatible = true;
	CompatibleExecutableResults current = CompatibleExecutableResults.EXACT;
	for (int i = 0; i < constructorParameterTypes.length; i++) {
	Class<?> providedType = providedTypes[i];
	Class<?> parameterType = constructorParameterTypes[i];

	// null can't be used as primitive
	if ((providedType == null) && parameterType.isPrimitive()) {
	return CompatibleExecutableResults.INVALID;
	}

	// handle primitives correctly by using wrapped type as boolean.class.isAssignableFrom(Boolean.class) => false
	if ((providedType != null) && ! getWrapperClass(parameterType).isAssignableFrom(providedType)) {
	return CompatibleExecutableResults.INVALID;
	}

	if ((providedType == null) \|\| parameterType.equals(providedType)) {
	continue; // sill exact match
	}
	current = CompatibleExecutableResults.COMPATIBLE;
	}
	return current;
	}

	private enum CompatibleExecutableResults {
	EXACT,
	COMPATIBLE,
	INVALID
	}

	private static Class<?> getWrapperClass(Class<?> clazz) {
	if (! clazz.isPrimitive()) {
	return clazz;
	}
	if (clazz == boolean.class) {
	return Boolean.class;
	}
	if (clazz == byte.class) {
	return Byte.class;
	}
	if (clazz == short.class) {
	return Short.class;
	}
	if (clazz == char.class) {
	return Character.class;
	}
	if (clazz == int.class) {
	return Integer.class;
	}
	if (clazz == long.class) {
	return Long.class;
	}
	if (clazz == float.class) {
	return Float.class;
	}
	if (clazz == double.class) {
	return Double.class;
	}
	throw new Error("Unknown primitive type?"); // not possible?
	}
	}