首先是一些上下文:下面粘贴的所有代码都在另一个声明为的类中public class TheClass extends SomeProprietaryClass.我不能出于各种原因在另一个文件中声明这些类...并且日志消息是法语.而且我是一个"最后快乐"的程序员.这是问题的核心......
现在,代码......(可能太多了 - 按要求剥离只保留相关部分)
自定义异常:
private static final class BreadCrumbException
extends Exception
{
private BreadCrumbException(final String message)
{
super(message);
}
private BreadCrumbException(final String message, final Throwable cause)
{
super(message, cause);
}
}
用于"实现"面包屑元素可见性的枚举:
private enum Visibility
{
MAINPAGE("R"),
MENU("M"),
BREADCRUMB("A"),
COMMERCIAL("C");
private static final Map<String, Visibility> reverseMap
= new HashMap<String, Visibility>();
private static final String characterClass;
static {
final StringBuilder sb = new StringBuilder("[");
for (final Visibility v: values()) {
reverseMap.put(v.flag, v);
sb.append(v.flag);
}
sb.append("]");
characterClass = sb.toString();
}
private final String flag;
Visibility(final String flag)
{
this.flag = flag;
}
static EnumSet<Visibility> fromBC(final String element)
{
final EnumSet<Visibility> result = EnumSet.noneOf(Visibility.class);
for (final String s: reverseMap.keySet())
if (element.contains(s))
result.add(reverseMap.get(s));
return result;
}
static String asCharacterClass()
{
return characterClass;
}
static String asString(final EnumSet<Visibility> set)
{
final StringBuilder sb = new StringBuilder();
for (final Visibility v: set)
sb.append(v.flag);
return sb.toString();
}
@Override
public String toString()
{
return flag;
}
}
面包屑元素:
private static class BreadCrumbElement
{
private static final Pattern p
= Pattern.compile(String.format("(%s+)(\\d+)",
Visibility.asCharacterClass()));
private final String element;
private final String menuID;
private final EnumSet<Visibility> visibility;
BreadCrumbElement(final String element)
{
final Matcher m = p.matcher(element);
if (!m.matches())
throw new IllegalArgumentException("Élément de fil d'ariane invalide: " + element);
this.element = element;
visibility = EnumSet.copyOf(Visibility.fromBC(m.group(1)));
menuID = m.group(2);
}
public boolean visibleFrom(final Visibility v)
{
return visibility.contains(v);
}
@Override
public boolean equals(final Object o)
{
if (this == o)
return true;
if (o == null || getClass() != o.getClass())
return false;
final BreadCrumbElement that = (BreadCrumbElement) o;
return element.equals(that.element);
}
@Override
public int hashCode()
{
return element.hashCode();
}
@Override
public String toString()
{
return element;
}
public String getMenuID()
{
return menuID;
}
}
面包屑:
private static class BreadCrumb
implements Iterable<BreadCrumbElement>
{
private static final BreadCrumb EMPTY = new BreadCrumb();
private final List<BreadCrumbElement> elements
= new LinkedList<BreadCrumbElement>();
private String bc;
BreadCrumb(final String bc)
throws BreadCrumbException
{
final Set<BreadCrumbElement> set = new HashSet<BreadCrumbElement>();
BreadCrumbElement e;
for (final String element: bc.split("\\s+")) {
e = new BreadCrumbElement(element);
if (!set.add(e))
throw new BreadCrumbException("Élément dupliqué "
+ "dans le fil d'Ariane : " + element);
elements.add(e);
}
if (elements.isEmpty())
throw new BreadCrumbException("Fil d'ariane vide!");
if (!elements.get(0).visibleFrom(Visibility.MAINPAGE))
throw new BreadCrumbException("Le fil d'Ariane ne "
+ "commence pas à l'accueil : " + bc);
set.clear();
this.bc = bc;
}
private BreadCrumb()
{
}
BreadCrumb reverse()
{
final BreadCrumb ret = new BreadCrumb();
ret.elements.addAll(elements);
Collections.reverse(ret.elements);
ret.bc = StringUtils.join(ret.elements, " ");
return ret;
}
public Iterator<BreadCrumbElement> iterator()
{
return elements.iterator();
}
@Override
public String toString()
{
return bc;
}
}
面包屑渲染器的接口:
public interface BreadCrumbRender
{
List<CTObjectBean> getBreadCrumb()
throws Throwable;
String getTopCategory();
String getMenuRoot();
String getContext();
}
上面的接口的实现是我的问题的根源:
private class CategoryBreadCrumbRender
implements BreadCrumbRender
{
private final BreadCrumb bc;
private final CTObject object;
CategoryBreadCrumbRender(final CTObject object)
{
this.object = object;
final String property;
// FIELD_BC is declared as a private static final String earlier on.
// logger is also a private static final Logger
try {
property = object.getProperty(FIELD_BC);
} catch (Throwable throwable) {
logger.fatal("Impossible d'obtenir le champ " + FIELD_BC
+ " de l'objet", throwable);
bc = BreadCrumb.EMPTY;
return;
}
try {
bc = new BreadCrumb(property);
} catch (BreadCrumbException e) {
logger.fatal("Impossible d'obtenir le fil d'Ariane", e);
bc = BreadCrumb.EMPTY; // <-- HERE
}
}
// ....
在// <-- HERE上面标记的点上,我使用的Intellij IDEA和javac(1.6.0.29)都告诉我Variable bc might already have been assigned to,这被认为是一个错误(事实上,代码不能编译).
麻烦的是,我不明白为什么......我的理由如下:
.getProperty()抛出Throwable),当捕获异常时,bc被成功分配,然后我返回,到目前为止这么好;bc是最终的:在try块中的赋值不会发生(？)但是在抓住块而不是......除了否,它没有.由于IDEA和javac都不同意我的意见,他们肯定是对的.但为什么？
(而且,在课堂BreadCrumb.EMPTY上宣布private static final,我想知道我怎么可以访问它...附属问题)
编辑:final关键字有一个已知的错误(这里,感谢@MiladNaseri链接到它),但应该注意,在这个错误中,变量v只在catch块中分配- 但在上面的代码中,我分配它在try块中,只有在catch抛出异常时才以块的形式分配它.此外,应该注意,错误仅发生在第二catch块中.
好的,假设在第一个try块中,property = object.getProperty(FIELD_BC);发生异常时.因此,JVM将进入catch块,并bc沿途进行初始化.
然后在第二个try块中,也会发生异常,从而导致BreadCrumb.EMPTY被分配,从而bc有效地覆盖其原始值.
现在,这bc 可能已经被初始化了.我希望你能看到我来自哪里.
由于JAVAC分析引擎没有区分try块内的一个或多个语句,因此它不会看到您的情况与下面的不同:
try {
bc = null;
String x = null;
System.out.println(x.toString());
} catch (Throwable e) {
bc = null;
}
在这种情况下,bc 将被分配两次.换句话说,JAVAC不关心Throwable谎言的来源,它只关心它可以存在,并且bc可能在该try块中成功分配.