Bug 126705 [Preferences] FileFieldEditor does not call doCheckState
org.eclipse.jface.preference.FileFieldEditor does not call doCheckSate() during checkState() which makes it difficult to subclass this editor to perform additional checks like it is possible with StringFieldEditor
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/FileFieldEditor.java
/**
     * List of legal file extension suffixes, or <code>null</code>
     * for system defaults.
     */
    private String[] extensions = null;
    /**
     * Indicates whether the path must be absolute;
     * <code>false</code> by default.
     */
    private boolean enforceAbsolute = false;
    /**
     * Creates a new file field editor 
     */
    protected FileFieldEditor() {
    }
    /**
     * Creates a file field editor.
     * 
     * @param name the name of the preference this field editor works on
     * @param labelText the label text of the field editor
     * @param parent the parent of the field editor's control
     */
    public FileFieldEditor(String name, String labelText, Composite parent) {
        this(name, labelText, false, parent);
    }
    
    /**