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Finds unused classes of a project

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package de.is24.guava;

import com.google.common.base.Function;
import com.google.common.base.Optional;
import de.is24.deadcode4j.Utils;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

/**
 * Provides convenience methods for {@link de.is24.guava.NonNullFunction}.
 *
 * @since 2.0.0
 */
public final class NonNullFunctions {

    private NonNullFunctions() {}

    /**
     * Returns a NonNullFunction that will call the specified functions one by one until a return value is
     * present or the end of the call chain is reached.
     *
     * @since 2.0.0
     */
    @Nonnull
    public static  NonNullFunction> or(@Nonnull final NonNullFunction>... functions) {
        return new NonNullFunction>() {
            @Nonnull
            @Override
            public Optional apply(@Nonnull F input) {
                for (int i = 0; ; ) {
                    Optional result = functions[i++].apply(input);
                    if (result.isPresent() || i == functions.length) {
                        return result;
                    }
                }
            }
        };
    }

    /**
     * Transforms a NonNullFunction into a Function.
     * If a Function's input is null, a NullPointerException is thrown.
     *
     * @since 2.0.0
     */
    @Nonnull
    public static  Function toFunction(@Nonnull final NonNullFunction nonNullFunction) {
        return new Function() {
            @Nullable
            @Override
            @SuppressWarnings("ConstantConditions")
            public T apply(@Nullable F input) {
                return nonNullFunction.apply(Utils.checkNotNull(input));
            }
        };
    }

}