除了上面提到的基本区别之外，在类中的instanceof操作符和isAssignableFrom方法之间还有一个核心的微妙区别。

Read instanceof as “is this (the left part) the instance of this or any subclass of this (the right part)” and read x.getClass().isAssignableFrom(Y.class) as “Can I write X x = new Y()”. In other words, instanceof operator checks if the left object is same or subclass of right class, while isAssignableFrom checks if we can assign object of the parameter class (from) to the reference of the class on which the method is called. Note that both of these consider the actual instance not the reference type.

考虑一个A、B和C三个类的例子，其中C扩展了B, B扩展了A。

B b = new C();

System.out.println(b instanceof A); //is b (which is actually class C object) instance of A, yes. This will return true.  
System.out.println(b instanceof B); // is b (which is actually class C object) instance of B, yes. This will return true.  
System.out.println(b instanceof C); // is b (which is actually class C object) instance of C, yes. This will return true. If the first statement would be B b = new B(), this would have been false.
System.out.println(b.getClass().isAssignableFrom(A.class));//Can I write C c = new A(), no. So this is false.
System.out.println(b.getClass().isAssignableFrom(B.class)); //Can I write C c = new B(), no. So this is false.
System.out.println(b.getClass().isAssignableFrom(C.class)); //Can I write C c = new C(), Yes. So this is true.

这完全取决于代码中此时可用的内容。我不建议使用isAssignableFrom如果你正在使用一个实际的对象-有一个更好的选择。下面是一份根据你所拥有的产品进行排名的推荐列表:

如果你有一个对象a，并且你在编译时知道类型B: a instanceof实例 如果你有一个对象a，你不知道类型B，但你有一个对象B: .isInstance b.getClass () () 如果你有一个对象a，在编译时没有类型或实例化对象，但你有一个类对象class <?> someBClass: someBClass.isInstance (a) 如果你没有实例化对象，但是你有两个Class<?>对象: someBClass.isAssignableFrom (someAClass)。

假设你从列表的顶部开始，然后往下做，每一种方法都是实现目标的最简单的方法，根据我自己的研究，我相信你也会得到最好的表现。

我们在团队中做的一些测试表明，A.class. isassignablefrom (B. getclass())比B instanceof a工作得更快，如果你需要对大量元素进行检查，这是非常有用的。

Instanceof只能用于引用类型，不能用于基本类型。isAssignableFrom()可以用于任何类对象:

a instanceof int  // syntax error
3 instanceof Foo  // syntax error
int.class.isAssignableFrom(int.class)  // true

看到http://java.sun.com/javase/6/docs/api/java/lang/Class.html isAssignableFrom (. lang . class)。

isAssignableFrom(A, B) =

if (A == B) return true
else if (B == java.lang.Object) return false
else return isAssignableFrom(A, getSuperClass(B))

The pseudo code above is a definition of, if references of type/class A is assignable from references of type/class B. It is a recursive definition. To some it may be helpful, for others it may be confusing. I add it in case somebody should find it useful. This is just an attempt to capture my understanding, it is not the official definition. It is used in a certain Java VM implementation and works for many example programs, so while I cannot guarentee that it captures all aspects of isAssignableFrom, it is not completely off.

除了上面提到的基本区别之外，在类中的instanceof操作符和isAssignableFrom方法之间还有一个核心的微妙区别。

Read instanceof as “is this (the left part) the instance of this or any subclass of this (the right part)” and read x.getClass().isAssignableFrom(Y.class) as “Can I write X x = new Y()”. In other words, instanceof operator checks if the left object is same or subclass of right class, while isAssignableFrom checks if we can assign object of the parameter class (from) to the reference of the class on which the method is called. Note that both of these consider the actual instance not the reference type.

考虑一个A、B和C三个类的例子，其中C扩展了B, B扩展了A。

B b = new C();

System.out.println(b instanceof A); //is b (which is actually class C object) instance of A, yes. This will return true.  
System.out.println(b instanceof B); // is b (which is actually class C object) instance of B, yes. This will return true.  
System.out.println(b instanceof C); // is b (which is actually class C object) instance of C, yes. This will return true. If the first statement would be B b = new B(), this would have been false.
System.out.println(b.getClass().isAssignableFrom(A.class));//Can I write C c = new A(), no. So this is false.
System.out.println(b.getClass().isAssignableFrom(B.class)); //Can I write C c = new B(), no. So this is false.
System.out.println(b.getClass().isAssignableFrom(C.class)); //Can I write C c = new C(), Yes. So this is true.