Instanceof也不能用于基本类型或泛型类型。如下代码所示:

//Define Class< T > type ... 

Object e = new Object();

if(e instanceof T) {
  // Do something.
}

错误是:不能对类型参数t执行instanceof检查，而是使用它的erasure对象，因为进一步的泛型类型信息将在运行时被擦除。

由于删除运行时引用的类型擦除而无法编译。然而，下面的代码将编译:

if( type.isAssignableFrom(e.getClass())){
  // Do something.
}

Instanceof也不能用于基本类型或泛型类型。如下代码所示:

//Define Class< T > type ... 

Object e = new Object();

if(e instanceof T) {
  // Do something.
}

错误是:不能对类型参数t执行instanceof检查，而是使用它的erasure对象，因为进一步的泛型类型信息将在运行时被擦除。

由于删除运行时引用的类型擦除而无法编译。然而，下面的代码将编译:

if( type.isAssignableFrom(e.getClass())){
  // Do something.
}

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.

还有一个不同之处。如果要测试的类型(Class)是动态的，例如，作为方法参数传递，那么instanceof将不会为你切割它。

boolean test(Class clazz) {
   return (this instanceof clazz); // clazz cannot be resolved to a type.
}

但是你可以:

boolean test(Class clazz) {
   return (clazz.isAssignableFrom(this.getClass())); // okidoki
}

哎呀，这个答案已经讲过了。也许这个例子对某人有帮助。

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.

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)。