https://github.com/javaee/jpa-spec: Java(TM) Persistence API 
Copyright (c) 2008 - 2013 Oracle Corporation. All rights reserved.
This program and the accompanying materials are made available under the
terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
which accompanies this distribution.
The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
and the Eclipse Distribution License is available at
http://www.eclipse.org/org/documents/edl-v10.php.
Contributors:
    Linda DeMichiel - Java Persistence 2.1
    Linda DeMichiel - Java Persistence 2.0

/*******************************************************************************
 * Copyright (c) 2008 - 2013 Oracle Corporation. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *     Linda DeMichiel - Java Persistence 2.1
 *     Linda DeMichiel - Java Persistence 2.0
 *
 ******************************************************************************/ 
package javax.persistence.metamodel;


Instances of the type SingularAttribute represents persistent 
single-valued properties or fields.

Type parameters:
  • <X> – The type containing the represented attribute
  • <T> – The type of the represented attribute
Since:Java Persistence 2.0
/**
 * Instances of the type <code>SingularAttribute</code> represents persistent 
 * single-valued properties or fields.
 *
 * @param <X> The type containing the represented attribute
 * @param <T> The type of the represented attribute
 *
 * @since Java Persistence 2.0
 */
public interface SingularAttribute<X, T> 
		extends Attribute<X, T>, Bindable<T> {
	
    
 Is the attribute an id attribute.  This method will return
 true if the attribute is an attribute that corresponds to
 a simple id, an embedded id, or an attribute of an id class.
 @return boolean indicating whether the attribute is an id

/**
     *  Is the attribute an id attribute.  This method will return
     *  true if the attribute is an attribute that corresponds to
     *  a simple id, an embedded id, or an attribute of an id class.
     *  @return boolean indicating whether the attribute is an id
     */
    boolean isId();

    
 Is the attribute a version attribute.
 @return boolean indicating whether the attribute is 
         a version attribute

/**
     *  Is the attribute a version attribute.
     *  @return boolean indicating whether the attribute is 
     *          a version attribute
     */
    boolean isVersion();

    
 Can the attribute be null.
 @return boolean indicating whether the attribute can
         be null

/** 
     *  Can the attribute be null.
     *  @return boolean indicating whether the attribute can
     *          be null
     */
    boolean isOptional();

    
Return the type that represents the type of the attribute.

Returns:type of attribute
/**
     * Return the type that represents the type of the attribute.
     * @return type of attribute
     */
    Type<T> getType();
}