framework/src/net/sf/tapestry/IBinding.java

//
// Tapestry Web Application Framework
// Copyright (c) 2000-2002 by Howard Lewis Ship
//
// Howard Lewis Ship
// http://sf.net/projects/tapestry
// mailto:hship@users.sf.net
//
// This library is free software.
//
// You may redistribute it and/or modify it under the terms of the GNU
// Lesser General Public License as published by the Free Software Foundation.
//
// Version 2.1 of the license should be included with this distribution in
// the file LICENSE, as well as License.html. If the license is not
// included with this distribution, you may find a copy at the FSF web
// site at 'www.gnu.org' or 'www.fsf.org', or you may write to the
// Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139 USA.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied waranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//

package net.sf.tapestry;

import java.util.Collection;

/**
 *  A binding is the mechanism used to provide values for parameters of
 *  specific {@link IComponent} instances. The component doesn't
 *  care where the required value comes from, it simply requires that
 *  a value be provided when needed.
 *
 *  <p>Bindings are set inside the containing component's specification.
 *  Bindings may be static or dynamic (though that is irrelevant to the
 *  component).  Components may also use a binding to write a value
 *  back through a property to some other object (typically, another component).
 *
 *  @author Howard Lewis Ship
 *  @version $Id$
 **/

public interface IBinding
{
    /**
     *  Invokes {@link #getObject()}, then coerces the value to a boolean.  
     *  The following rules are used to perform the coercion:
     *  <ul>
     *  <li>null is always false
     *  <li>A {@link Boolean} value is self-evident
     *  <li>A {@link Number} value is true if non-zero
     *  <li>A {@link String} value is true if non-empty and contains
     *  non-whitespace characters
     *  <li>Any {@link Collection} value is true if it has a non-zero
     *  {@link Collection#size() size}
     *  <li>Any array type is true if it has a non-zero length
     *  <li>Any other non-null value is true
     *  </ul>
     **/

    public boolean getBoolean();

    /**
     *  Gets the value of the Binding using {@link #getObject} and coerces it
     *  to an <code>int</code>.  Strings will be parsed, and other
     *  <code>java.lang.Number</code> classes will have <code>intValue()</code>
     *  invoked.  
     *
     *  @throws ClassCastException if the binding's value is not of a usable class.
     *  @throws NullValueForBindingException if the binding's value is null.
     **/

    public int getInt();

    /**
     *  Gets the value of the Binding using {@link #getObject()} and coerces it
     *  to a <code>double</code>.  Strings will be parsed, and other
     *  <code>java.lang.Number</code> classes will have <code>doubleValue()</code>
     *  invoked.
     *
     *  @throws ClassCastException if the binding's value is not of a usable class.
     *  @throws NullValueForBindingException if the binding's value is null.
     **/

    public double getDouble();

    /**
     *  Invokes {@link #getObject()} and converts the result to <code>java.lang.String</code>.
     **/

    public String getString();

    /**
     *  Returns the value of this binding.  This is the essential method.  Other methods
     *  get this value and cast or coerce the value.
     *
     **/

    public Object getObject();

    /**
     *  Returns the value for the binding after performing some basic checks.
     *
     *  @param parameterName the name of the parameter (used to build
     *  the message if an exception is thrown).
     *  @param type if not null, the value must be assignable to the specific
     *  class
     *  @throws BindingException if the value is not assignable to the
     *  specified type
     *
     *  @since 0.2.9
     **/

    public Object getObject(String parameterName, Class type);

    /**
     *  Returns true if the value is statically defined.  Static values
     *  are always read-only.
     *
     *  @deprecated use {@link #isInvariant()} instead.
     **/

    public boolean isStatic();


	/**
	 *  Returns true if the value is invariant (not changing; the
	 *  same value returned each time).  Static and field bindings
	 *  are always invariant, and property bindings may be
	 *  marked invariant (as an optimization).
	 * 
	 *  @since 2.0.3
	 * 
	 **/
	
	public boolean isInvariant();

    /**
     *  Constructs a <code>Boolean</code> and invokes {@link #setObject(Object)}.
     *
     **/

    public void setBoolean(boolean value);

    /**
     *  Constructs an <code>Integer</code> and invokes {@link #setObject(Object)}.
     *
     **/

    public void setInt(int value);

    /**
     *  Constructs an <code>Double</code> and invokes {@link #setObject(Object)}.
     *
     **/

    public void setDouble(double value);

    /**
     *  Invokes {@link #setObject(Object)}.
     *
     **/

    public void setString(String value);

    /**
     *  Updates the value of the binding, if possible.
     *
     *  @exception ReadOnlyBindingException If the binding is read only.
     *
     **/

    public void setObject(Object value);

    /**
     *  Returns the type of the binding.  For static bindings, returns
     *  the actual type stored (this will be String for most static bindings,
     *  or the actual type of a field, for field bindings).
     *
     *  @since 1.0.5
     *
     **/

    public Class getType();
}