Java 如何在运行时检查子类是否是类的实例？
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How to check if a subclass is an instance of a class at runtime?
提问by iamamused
In an android app test suite I have a class like this where Bis a view:
在一个 android 应用测试套件中，我有一个这样的类，其中B有一个视图：
public class A extends B {
... etc...
}
now I have a list of view objects which may contain Aobjects but in this case I only care if they're subclasses or "instances of" B. I'd like to do something like:
现在我有一个可能包含A对象的视图对象列表，但在这种情况下，我只关心它们是子类还是“实例” B。我想做类似的事情：
ArrayList<View> viewList = getViews();
Iterator<View> iterator = viewList.iterator();
while (iterator.hasNext() && viewList != null) {
View view = iterator.next();
if (view.getClass().isInstance(B.class)) {
// this is an instance of B
}
}
The problem is that when the ifencounters an Aobject it doesn't evaluate to an "instance of B". Is there a way to do isSubclassOfor something?
问题是当if遇到一个A对象时，它不会评估为“实例B”。有什么办法isSubclassOf吗？
采纳答案by Hardcoded
You have to read the API carefully for this methods. Sometimes you can get confused very easily.
您必须仔细阅读这些方法的 API。有时，您很容易感到困惑。
It is either:
它是：
if (B.class.isInstance(view))
API says: Determines if the specified Object(the parameter)is assignment-compatible with the object represented by this Class(The class object you are calling the method at)
API说：确定是否指定的Object （参数）是分配兼容由表示的对象此Class （类对象要调用的方法）
or:
或者：
if (B.class.isAssignableFrom(view.getClass()))
API says: Determines if the class or interface represented by this Class objectis either the same as, or is a superclass or superinterface of, the class or interface represented by the specified Class parameter
API 说：确定此Class 对象表示的类或接口是否与指定的 Class 参数表示的类或接口相同，或者是其超类或超接口
or (without reflection and the recommended one):
或（没有反思和推荐的）：
if (view instanceof B)
回答by Kris
if(view instanceof B)
This will return true if view is an instance of B or the subclass A (or any subclass of B for that matter).
如果视图是 B 或子类 A（或 B 的任何子类）的实例，则返回 true。
回答by Joachim Sauer
Maybe I'm missing something, but wouldn't this suffice:
也许我错过了一些东西，但这还不够：
if (view instanceof B) {
// this view is an instance of B
}
回答by nanda
It's the other way around: B.class.isInstance(view)
反过来说： B.class.isInstance(view)
回答by chama
I've never actually used this, but try view.getClass().getGenericSuperclass()
我从来没有真正使用过这个，但试试 view.getClass().getGenericSuperclass()
回答by Michael Borgwardt
Class.isAssignableFrom()- works for interfaces as well. If you don't want that, you'll have to call getSuperclass()and test until you reach Object.
Class.isAssignableFrom()- 也适用于接口。如果您不希望那样，则必须调用getSuperclass()并进行测试，直到到达Object.
回答by vientoho
If there is polymorphism such as checking SQLRecoverableException vs SQLException, it can be done like that.
如果存在多态性，例如检查 SQLRecoverableException 与 SQLException，则可以这样做。
try {
// sth may throw exception
....
} catch (Exception e) {
if(SQLException.class.isAssignableFrom(e.getCause().getClass()))
{
// do sth
System.out.println("SQLException occurs!");
}
}
Simply say,
简单地说，
ChildClass child= new ChildClass();
if(ParentClass.class.isAssignableFrom(child.getClass()))
{
// do sth
...
}
