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

/*
 *  ====================================================================
 *  The Apache Software License, Version 1.1
 *
 *  Copyright (c) 2002 The Apache Software Foundation.  All rights
 *  reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *  notice, this list of conditions and the following disclaimer.
 *
 *  2. Redistributions in binary form must reproduce the above copyright
 *  notice, this list of conditions and the following disclaimer in
 *  the documentation and/or other materials provided with the
 *  distribution.
 *
 *  3. The end-user documentation included with the redistribution,
 *  if any, must include the following acknowledgment:
 *  "This product includes software developed by the
 *  Apache Software Foundation (http://www.apache.org/)."
 *  Alternately, this acknowledgment may appear in the software itself,
 *  if and wherever such third-party acknowledgments normally appear.
 *
 *  4. The names "Apache" and "Apache Software Foundation" and
 *  "Apache Tapestry" must not be used to endorse or promote products
 *  derived from this software without prior written permission. For
 *  written permission, please contact apache@apache.org.
 *
 *  5. Products derived from this software may not be called "Apache",
 *  "Apache Tapestry", nor may "Apache" appear in their name, without
 *  prior written permission of the Apache Software Foundation.
 *
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 *  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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 *  ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 *  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 *  OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 *  SUCH DAMAGE.
 *  ====================================================================
 *
 *  This software consists of voluntary contributions made by many
 *  individuals on behalf of the Apache Software Foundation.  For more
 *  information on the Apache Software Foundation, please see
 *  <http://www.apache.org/>.
 */
package net.sf.tapestry;

/**
 *  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 invariant (not changing; the
	 *  same value returned each time).  Static and field bindings
	 *  are always invariant, and {@link net.sf.tapestry.binding.ExpressionBinding}s
     *  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);

}