code: package us.msu.cse.repair.ec.operators.crossover;
  
  import java.util.Arrays;
  import java.util.HashMap;
  import java.util.List;
  
  import jmetal.core.Solution;
  import jmetal.operators.crossover.Crossover;
  import jmetal.util.Configuration;
  import jmetal.util.JMException;
  import jmetal.util.PseudoRandom;
  import us.msu.cse.repair.ec.representation.GenProgSolutionType;
  import us.msu.cse.repair.ec.variable.Edits;
  
  public class GenProgSinglePointCrossover extends Crossover {
  	/**
  	 * 
  	 */
  	private static final long serialVersionUID = 1L;
  
  	private static final List<?> VALID_TYPES = Arrays.asList(GenProgSolutionType.class);
  
  	private Double crossoverProbability_ = null;
  
  	public GenProgSinglePointCrossover(HashMap<String, Object> parameters) {
  		super(parameters);
  		if (parameters.get("probability") != null)
  			crossoverProbability_ = (Double) parameters.get("probability");
  	} // SinglePointCrossover
  
  	public Solution[] doCrossover(double probability, Solution parent1, Solution parent2) throws JMException {
  		Solution[] offSpring = new Solution[2];
  		offSpring[0] = new Solution(parent1);
  		offSpring[1] = new Solution(parent2);
  
  		if (PseudoRandom.randDouble() < probability) {
  			List<Integer> p1_locList = ((Edits) parent1.getDecisionVariables()[0]).getLocList();
  			List<Integer> p1_opList = ((Edits) parent1.getDecisionVariables()[0]).getOpList();
  			List<Integer> p1_ingredList = ((Edits) parent1.getDecisionVariables()[0]).getIngredList();
  
  			List<Integer> p2_locList = ((Edits) parent2.getDecisionVariables()[0]).getLocList();
  			List<Integer> p2_opList = ((Edits) parent2.getDecisionVariables()[0]).getOpList();
  			List<Integer> p2_ingredList = ((Edits) parent2.getDecisionVariables()[0]).getIngredList();
  
  			List<Integer> c1_locList = ((Edits) offSpring[0].getDecisionVariables()[0]).getLocList();
  			List<Integer> c1_opList = ((Edits) offSpring[0].getDecisionVariables()[0]).getOpList();
  			List<Integer> c1_ingredList = ((Edits) offSpring[0].getDecisionVariables()[0]).getIngredList();
  
  			List<Integer> c2_locList = ((Edits) offSpring[1].getDecisionVariables()[0]).getLocList();
  			List<Integer> c2_opList = ((Edits) offSpring[1].getDecisionVariables()[0]).getOpList();
  			List<Integer> c2_ingredList = ((Edits) offSpring[1].getDecisionVariables()[0]).getIngredList();
  
  			int cut1 = PseudoRandom.randInt(0, p1_locList.size() - 1);
  			int cut2 = PseudoRandom.randInt(0, p2_locList.size() - 1);
  
  			swap(p1_locList, p2_locList, c1_locList, c2_locList, cut1, cut2);
  			swap(p1_opList, p2_opList, c1_opList, c2_opList, cut1, cut2);
  			swap(p1_ingredList, p2_ingredList, c1_ingredList, c2_ingredList, cut1, cut2);
  		}
  
  		return offSpring;
  	}
  
  	private void swap(List<Integer> p1List, List<Integer> p2List, List<Integer> c1List, List<Integer> c2List, int cut1,
  			int cut2) {
  		for (int i = c1List.size() - 1; i >= cut1; i--)
  			c1List.remove(c1List.size() - 1);
  		for (int i = c2List.size() - 1; i >= cut2; i--)
  			c2List.remove(c2List.size() - 1);
  
  		for (int i = cut2; i < p2List.size(); i++)
  			c1List.add(p2List.get(i));
  		for (int i = cut1; i < p1List.size(); i++)
  			c2List.add(p1List.get(i));
  	}
  
  	@Override
  	public Object execute(Object object) throws JMException {
  		Solution[] parents = (Solution[]) object;
  
  		if (!(VALID_TYPES.contains(parents[0].getType().getClass())
  				&& VALID_TYPES.contains(parents[1].getType().getClass()))) {
  
  			Configuration.logger_.severe("GenProgSinglePointCrossover.execute: the solutions "
  					+ "are not of the right type. The type should be 'GenProgSolutionType', but " + parents[0].getType()
  					+ " and " + parents[1].getType() + " are obtained");
  
  			Class<?> cls = java.lang.String.class;
  			String name = cls.getName();
  			throw new JMException("Exception in " + name + ".execute()");
  		} // if
  
  		if (parents.length < 2) {
  			Configuration.logger_.severe("GenProgSinglePointCrossover.execute: operator " + "needs two parents");
  			Class<?> cls = java.lang.String.class;
  			String name = cls.getName();
  			throw new JMException("Exception in " + name + ".execute()");
  		}
  
  		Solution[] offSpring;
  		offSpring = doCrossover(crossoverProbability_, parents[0], parents[1]);
  
  		// -> Update the offSpring solutions
  		for (int i = 0; i < offSpring.length; i++) {
  			offSpring[i].setCrowdingDistance(0.0);
  			offSpring[i].setRank(0);
  		}
  		return offSpring;
  	} // execute
  }
  