JAvaにおけるinstanceofの使い方
7271 ワード
instanceof
instanceof Java、php ( ), ==,>,< 。
, Java 。
, boolean 。
。 c# is 。
java instanceof 。
instanceof , 。
result = object instanceof class
Result: 。
Object: 。 。
Class: 。 。
object class , instanceof true。
object , object null, false。
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("
instanceoftest 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("
instanceoftest 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
:
String s = "I AM an Object!";
boolean isobject = s instanceof Object;
String , String , instanceof Object , , , true, isobject true。
instanceof 。 , :
public class Bill {// }
public class PhoneBill extends Bill {// }
public class GasBill extends Bill {// }
, Bill , 。 , Bill , instanceof :
public double calculate(Bill bill) {
if (bill instanceof PhoneBill) {
//
}
if (bill instanceof GasBill) {
//
}
...
}
。
, 。 , , 。 , :
public double calculate(PhoneBill bill) {
//
}
public double calculate(GasBill bill) {
//
}
, instanceof , 。
instanceof ,
:
class Manager extends Employee
----------------------------------------------------------
public void doSomething(Employee e) {
if ( e instanceof Manager){
Manager m = (Manager) e ;
}
}
1. Boolean , 。...instanceof ... Boolean , 。
2. instanceof ...instanceof ...
3.
4.