core/src/main/java/org/apache/commons/functor/core/Offset.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.functor.core;

import java.util.concurrent.atomic.AtomicInteger;

import org.apache.commons.functor.BinaryPredicate;
import org.apache.commons.functor.NullaryPredicate;
import org.apache.commons.functor.Predicate;
import org.apache.commons.lang3.Validate;

/**
 * A predicate that returns <code>false</code>
 * the first <i>n</i> times it is invoked, and
 * <code>true</code> thereafter.
 *
 * @since 1.0
 * @version $Revision$ $Date$
 */
public final class Offset implements NullaryPredicate, Predicate<Object>,
        BinaryPredicate<Object, Object> {
    // instance variables
    //---------------------------------------------------------------
    /**
     * The number of times the predicate must return {@code false}.
     */
    private final int min;
    /**
     * The current number of times the predicate has been invoked.
     */
    private AtomicInteger state = new AtomicInteger();

    /**
     * Create a new Offset.
     * @param count offset
     */
    public Offset(int count) {
        Validate.isTrue(count >= 0, "Argument must be a non-negative integer.");
        this.min = count;
    }

    /**
     * {@inheritDoc}
     */
    public boolean test() {
        // stop incrementing when we've hit max, so we don't loop around
        if (state.get() < min) {
            state.incrementAndGet();
            return false;
        }
        return true;
    }

    /**
     * {@inheritDoc}
     */
    public boolean test(Object obj) {
        return test();
    }

    /**
     * {@inheritDoc}
     */
    public boolean test(Object a, Object b) {
        return test();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof Offset)) {
            return false;
        }
        Offset other = (Offset) obj;
        return other.min == min;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public int hashCode() {
        int result = "Offset".hashCode();
        result <<= 2;
        result ^= min;
        return result;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String toString() {
        return "Offset<" + min + ">";
    }

    //default == equals/hashCode due to statefulness
}