Java instanceof用法详解及实例代码

packagecom.instanceoftest;

 interfaceA{}

 classBimplementsA{

 }

 classCextendsB {

 }

 classinstanceoftest {

 publicstaticvoidmain(String[] args){

   A a=null;

   B b=null;

   booleanres; 

   System.out.println("instanceoftest test case 1: ------------------");

    res = ainstanceofA; 

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

    res = binstanceofB;

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

   System.out.println("/ninstanceoftest test case 2: ------------------");  

   a=newB();

   b=newB();

   res = ainstanceofA; 

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

   res = ainstanceofB;

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

   res = binstanceofA;

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

   res = binstanceofB;

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

   System.out.println("/ninstanceoftest test case 3: ------------------");

   B b2=(C)newC();

   res = b2instanceofA;

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

   res = b2instanceofB;

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

   res = b2instanceofC;

   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

*/