Bug 52064 Content assist in "New Class" Dialog shows interfaces
Content Assist is available for the superclass in M7. However it also lists interfaces. If an interface is selected, the generated class "extends" it instead of "implementing" it.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/wizards/NewTypeWizardPage.java
/**
	 * Hook method that gets called from <code>createType</code> to retrieve 
	 * a type comment. This default implementation returns the content of the 
	 * 'type comment' template.
	 * 
	 * @return the type comment or <code>null</code> if a type comment 
	 * is not desired
     *
     * @since 3.0
	 */		
	protected String getTypeComment(ICompilationUnit parentCU, String lineDelimiter) {
		try {
			StringBuffer typeName= new StringBuffer();
			if (isEnclosingTypeSelected()) {
				typeName.append(JavaModelUtil.getTypeQualifiedName(getEnclosingType())).append('.');
			}
			typeName.append(getTypeName());
			String comment= CodeGeneration.getTypeComment(parentCU, typeName.toString(), lineDelimiter);
			if (comment != null && isValidComment(comment)) {
				return comment;
			}
		} catch (CoreException e) {
			JavaPlugin.log(e);
		}
		return null;
	}
	
	/**
	 * @deprecated Use getTypeComment(ICompilationUnit, String)