Java中instanceof关键字的用法总结

package com.instanceoftest;
interface A{}
class B implements A{

}
class C extends B {

}

class instanceoftest {
public static void main(String[] args){
A a=null;
B b=null;
boolean res;

System.out.println("instanceoftest test case 1: ------------------");
res = a instanceof A;
System.out.println("a instanceof A: " + res);

res = b instanceof B;
System.out.println("b instanceof B: " + res);

System.out.println("\ninstanceoftest test case 2: ------------------");
a=new B();
b=new B();

res = a instanceof A;
System.out.println("a instanceof A: " + res);

res = a instanceof B;
System.out.println("a instanceof B: " + res);
res = b instanceof A;
System.out.println("b instanceof A: " + res);

res = b instanceof B;
System.out.println("b instanceof B: " + res);

System.out.println("\ninstanceoftest test case 3: ------------------");
B b2=(C)new C();

res = b2 instanceof A;
System.out.println("b2 instanceof A: " + res);

res = b2 instanceof B;
System.out.println("b2 instanceof B: " + res);

res = b2 instanceof C;
System.out.println("b2 instanceof C: " + res);
}
}

/*
result:

instanceoftest test case 1: ------------------
a instanceof A: false
b instanceof B: false
instanceoftest test case 2: ------------------
a instanceof A: true
a instanceof B: true
b instanceof A: true
b instanceof B: true
instanceoftest test case 3: ------------------
b2 instanceof A: true
b2 instanceof B: true
b2 instanceof C: true

  Animal dog=new Dog();
  Animal cat=new Cat();

  List list = new ArrayList();

  list.add(dog);
  list.add(cat);

  Iterator it = list.iterator();
  while (it.hasNext()) {
     it.next().animalDo();

  }

  Station s = new Station();
  Cell c = new Cell();

  List list = new ArrayList();

  list.add(s);
  list.add(c);

  Iterator it = list.iterator();
  while (it.hasNext()) {
   Object obj = it.next();
   if (obj instanceof Station ) {
    Station s1 = (Station ) obj;
    s1.stationDo();
   }
   if (obj instanceof Cell ) {
    Cell c1 = (Cell ) obj;
    c1.cellDo();
   }
  }