Doubt from Khalid Mughal

[lalit upadheyay]

Hi,

In the following code :

  
class InvalidHoursException extends Exception{}
class NegativeHoursException extends InvalidHoursException{}
class ZeroHoursException extends InvalidHoursException{}
class Light
{
protected String billType="small bill";  
protected double getBill(int hours) throws InvalidHoursException//1
{ 
if (hours <0)
throw new InvalidHoursException();
System.out.println(10.0 * hours);
return 10.0 * hours;
}
public static void printBillType() {System.out.println("small bill");}//2
public void banner(){}
}
 
class TubeLight extends Light
{
public static String billType="large bill";  
public double getBill(int hours) throws ZeroHoursException//3
{ 
if (hours ==0)
throw new ZeroHoursException();
System.out.println(100.0 * hours);
return 100.0 * hours;
}
public static void printBillType() {System.out.println(billType);}//4
public double getBill(){ return 0.0;}
}
class NeonLight extends TubeLight
{
public void demonstrate() throws InvalidHoursException
{
((Light) this).getBill(20);//invokes method at 3
((Light) this).printBillType();//invokes method at 2
}
}
 
public class Client
{
public static void main(String[] args) throws InvalidHoursException
{

NeonLight nl=new NeonLight();
nl.demonstrate();
}
}

How is the method call at line 1 in demonstarte() method of NeonLight class different than the method call at the next line ? Though both the methods are available in TubeLight and Light classes, but the first line in demonstrate() invokes method from TubeLight and next line invokes method from Light. Please help.

[Shivakanth Thyagarajan]

The method follows the principle of Overriding ( i,e the getBill method ), it is resolved at run time.

The second method is a static method( i,e printAll( ) ) which gets resolved at compile time therefore the output.

Important Note:
Static methods are resolved at compile time, therefore cannot be overridden .