code: package org.optsol.project_scheduling.mrcpsp.fct.constraints;
  
  import com.google.ortools.linearsolver.MPConstraint;
  import com.google.ortools.linearsolver.MPSolver;
  import com.google.ortools.linearsolver.MPVariable;
  import java.util.Collection;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Set;
  import java.util.stream.Collectors;
  import org.optsol.jdecor.core.AbstractVariableManager;
  import org.optsol.jdecor.ortools.AbstractOrtoolsConstraintManager;
  import org.optsol.project_scheduling.mrcpsp.constants.sub.IConstants_B_k;
  import org.optsol.project_scheduling.mrcpsp.constants.sub.IConstants_R;
  import org.optsol.project_scheduling.mrcpsp.constants.sub.IConstants_V;
  import org.optsol.project_scheduling.mrcpsp.fct.variables.DecisionVars_Fct;
  
  public class FCT_i_FixInitialFlows<CONST extends IConstants_V & IConstants_R & IConstants_B_k>
      extends AbstractOrtoolsConstraintManager<CONST> {
  
    public FCT_i_FixInitialFlows() {
      super("j", "k");
    }
  
    @Override
    protected Collection<ConstraintKey> createKeys(CONST constants) {
      Set<ConstraintKey> indexes = new HashSet<>();
      List<Integer> A_0 =
          constants.get_V().stream()
              .filter(j -> j < constants.get_A_bar())
              .collect(Collectors.toList());
  
      for (Integer j : A_0) {
        for (int k : constants.get_R()) {
          indexes.add(new ConstraintKey(j, k));
        }
      }
      return indexes;
    }
  
    @Override
    protected void configureConstraint(
        MPConstraint constraint,
        CONST constants,
        AbstractVariableManager<MPSolver, MPVariable> variables,
        ConstraintKey index) throws Exception {
  
      int j = index.get("j");
      int k = index.get("k");
  
      MPVariable var =
          variables.getVar(DecisionVars_Fct.f, constants.get_A_bar(), j, k);
  
      if (j == constants.get_dummy_activity_project_start()) {
        var.setUb(constants.get_B_k(k));
        var.setLb(constants.get_B_k(k));
      } else {
        var.setUb(0.);
        var.setLb(0.);
      }
    }
  }
  