instanceof 的语法格式如下：
myobject instanceof ExampleClass
myobject：某类的对象引用
ExampleClass：某个类
class Quadrangle{
public static void draw(Quadrangle q) {
}
}
class Square extends Quadrangle {
}
class Anything {
}
public class Parallelogram extends Quadrangle {
public static void main(String[] args) {
Quadrangle q = new Quadrangle();
//判断父类对象是否为Parallelogram子类的一个实例
if(q instanceof Parallelogram) {
Parallelogram p = (Parallelogram) q;
}
if(q instanceof Square){
Square s = (Square)q;
}
}
}