instanceof attempts to downcast : instanceof Operator « Operators « SCJP

Home
SCJP
1.Java Source And Data Type
2.Operators
3.Modifiers
4.Type Casting
5.Statements
6.Object Oriented
7.Thread
8.Utility Classes
9.File
SCJP » Operators » instanceof Operator 
2.7.13.instanceof attempts to downcast
class A { }

class MainClass extends A {
  public static void main (String [] args) {
    A myA = new MainClass();
    m2(myA);
  }
  public static void m2(A a) {
    if (a instanceof MainClass)
      ((MainClass)a).doBstuff();
  }
  public static void doBstuff() {
    System.out.println("'a'");
  }
}
 
'a'
2.7.instanceof Operator
2.7.1.instanceof operator determines whether or not a given object is an instance of a particular class.
2.7.2.The instanceof operator tests the class of an object at runtime.
2.7.3.Using instanceof operator in class hierarchy
2.7.4.You cannot use a java.lang.Class object reference.
2.7.5.You cannot use a String representing the name of the class as the right operand.
2.7.6.The right operand of instanceof may be an interface.
2.7.7.Using the instanceof operator to test whether a reference refers to an array.
2.7.8.This line is not legal: if (x instanceof [])
2.7.9.Determine whether an object is an array using the isArray() method of the Class class.
2.7.10.If the left argument of the instanceof operator is a null value, the instanceof test simply returns false;
2.7.11.The instanceof Operator: Objects always "know" what type they are.
2.7.12.instanceof is for object reference variables only
2.7.13.instanceof attempts to downcast
2.7.14.test whether the null reference is an instance of a class. This will always result in false.
2.7.15.instanceof Compiler Error
2.7.16.Operands and Results Using instanceof Operator
www.java2java.com | Contact Us
Copyright 2009 - 12 Demo Source and Support. All rights reserved.
All other trademarks are property of their respective owners.