inputarc.java

Rakiura JFern是一个非常轻型的带有模拟器的Petri网络框架

// This is copyrighted source file, part of Rakiura JFern package. 
// See the file LICENSE for copyright information and the terms and conditions
// for copying, distributing and modifications of Rakiura JFern package.
// Copyright (C) 1999-2002 by Mariusz Nowostawski and others  [http://www.rakiura.org]

package org.rakiura.cpn;

/**
 * Represents an input Arc in JFern Petri Net model.
 * 
 *<br><br>
 * InputArc.java<br>
 * Created: Mon Sep 25 11:49:12 2000<br>
 *
 *@author  <a href="[e-mail]">Mariusz Nowostawski</a>
 *@version 2.1.0 $Revision: 1.14 $
 *@since 1.0
 */
public class InputArc extends AbstractArc {

  /** Default guard. */
  private Guard guard = new Guard() {
      public boolean evaluate() {
        Multiset multiset = getMultiset();
        return (multiset.size() > 0); 
      }
    };
  
  /** Default expression. */
  private Expression expr = new Expression() {
      public void evaluate() {
        //System.out.println("*** JFERN WARNING: uninitialised input arc expression");
      }
    };



  /**/
  protected InputArc() {
  }
  
  /**/
  public InputArc(final Place aFrom, final Transition aTo) {
    super(aFrom, aTo);
    aTo.addInput(this);
    aFrom.addInput(this);
  }

  
  /**
   * Checks if this arc is enabled.
   *@return this call evaluates the guard, and returns 
   *  <code>true</code> if the arc is enabled, 
   *  <code>false</code> otherwise.
   */
  public boolean guard() {
    return this.guard.evaluate();
  }
  
  /**
   * Evaluates this arc expression. The actual result of this
   * expression evaluation is accessible from the context. The 
   * arc expression is evaluated many times during net simulation,
   * thus should not have any side effects, apart from selecting
   * tokens via {@link org.rakiura.cpn.Context} methods.
   */
  public void expression() {
    this.expr.evaluate();
  }

  /**
   * Sets a guard for this arc.
   *@param aGuard a guard.
   */ 
  public void setGuard(final Guard aGuard) {
    this.guard = aGuard;
  }
  
  /**
   * Sets the multiset expression.
   *@param anExpr an expression
   */  
  public void setExpression(final Expression anExpr){
    this.expr = anExpr;

  }

  /**
   * Visitor pattern.
   */
  public NetElement apply(NetVisitor aVisitor) {
    aVisitor.inputArc(this);
    return this;
  }




  /**
   * Represents an input arc multiset expression.
   * 
   *
   *@author  <a href="[e-mail]">Mariusz</a>
   *@version 2.1.0 $Revision: 1.14 $ $Date: 2002/05/30 15:01:39 $
   *@since 2.0
   */
  public abstract class Expression implements Context {
  
    /**
     * Evaluates this expression. This method implements the 
     * actual expression on the input arc, which given
     * a  multiset from an input place evaluates to a set 
     * of tokens (a single multiset). Picking up and binding
     * tokens is achieved via the {@link #var} method.
     */
    public abstract void evaluate();


    public void var(final String aVariable) {
      getContext().var(aVariable);
    }
    public void var(final int aNumber) {
      getContext().var(aNumber);
    }
    public Object get(final String aVariable) {
      return getContext().get(aVariable);
    }
    public Multiset getMultiset() {
      return getContext().getMultiset();
    }
  } // Expression



  /**
   * Represents a generic input arc guard.
   * Note, in JFern, due to pure Java based inscription
   * language, all the partial matches must be done
   * explicitely via input arc guards. In such a guard
   * no references other to variables from this arc
   * should be made.
   *
   *
   *@author  <a href="[e-mail]">Mariusz</a>
   *@version 2.1.0 $Revision: 1.14 $
   *@since 2.0
   */
  public abstract class Guard implements Context {

    /**
     * Guard function.
     *@return <code>true</code> if this guard evaluates 
     * to enabled transition/arc;
     * <code>false</code> otherwise.
     */
    public abstract boolean evaluate();


    public void var(final String aVariable) {
      getContext().var(aVariable);
    }
    public void var(final int aNumber) {
      getContext().var(aNumber);
    }
    public Object get(final String aVariable) {
      return getContext().get(aVariable);
    }
    public Multiset getMultiset() {
      return getContext().getMultiset();
    }
 
  } // Guard


} // InputArc
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