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The James core module is part of the James framework for optimization using local search metaheuristics in Java. The core contains general components to model problems, objectives and constraints, as well as generic algorithms to solve the problems. Moreover, the core provides implementations of specific utilities for subset selection.

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//  Copyright 2014 Herman De Beukelaer
//
//  Licensed 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.jamesframework.core.search.stopcriteria;

import java.util.concurrent.TimeUnit;
import org.jamesframework.core.search.Search;

/**
 * Stop criterion that limits the time without finding any improvement during a search run.
 * 
 * @author Herman De Beukelaer
 */
public class MaxTimeWithoutImprovement implements StopCriterion {

    // maximum time without improvement (in milliseconds)
    private final long maxTimeWithoutImprovement;
    
    /**
     * Create a stop criterion to limit the time without finding any improvement during a search run.
     * The given time should be at least 1 millisecond.
     * 
     * @param maxTimeWithoutImprovement maximum time without improvement
     * @param timeUnit corresponding time unit
     * @throws IllegalArgumentException if given time is smaller than 1 millisecond
     */
    public MaxTimeWithoutImprovement(long maxTimeWithoutImprovement, TimeUnit timeUnit){
        this.maxTimeWithoutImprovement = timeUnit.toMillis(maxTimeWithoutImprovement);
        // check at least 1 ms
        if(this.maxTimeWithoutImprovement <= 0){
            throw new IllegalArgumentException("Error while creating stop criterion: maximum time without improvement "
                                                + "should be at least 1 millisecond.");
        }
    }
    
    /**
     * Checks whether the maximum time without finding improvements has been exceeded for the given search.
     * 
     * @param search search for which the time without finding improvements has to be checked
     * @return true if the given search has exceeded the maximum time without improvement
     */
    @Override
    public boolean searchShouldStop(Search search) {
        return search.getTimeWithoutImprovement()> maxTimeWithoutImprovement;
    }
    
    @Override
    public String toString(){
        return "{max time without improvement: " + maxTimeWithoutImprovement + " ms}";
    }

}