Java Question

[ZoneFire]

Java Question (Dynamic Binding)

hour = ( ( h >= 0 && h < 24 ) ? h:0 )

may i know what is the function of the "?" in the syntax above?
thank you

 

[gab00n]

Well it is like an if statement, it's name is the conditional operator in
C++, probably the same in java.

So if you wanted to convert it into an if statement it would look like this.

 if(h>= 0 && h < 24)
{
    hour = h;
}
else
{
    hour = 0;
}

It is very handy for keeping the code nice and neat, i use it very often as a result. So the stuff infront of the ? is the condition that must be met in order for it to be true and for hour to = h, the stuff after : is the false part and hour will be assigned 0.

 

[ZoneFire]

so that means "?" is used to replace if statements...
hence, the code will look neat and better organised...
thank you

 

[ZoneFire]

can someone tell me about what is dynamic binding in Java?
i am not clear with this concept...
thank you

 

[gab00n]

It's the process of binding a function call to a particular instance method of a class. It is needed when the compiler determines that there is more than one possible instance method from one of many class's that could be executed by a particular function call. It is used so that you don't have to write conditional statements to choose which code should be executed.

 

[ZoneFire]

thanks for your explanation, gab00n
besides, i got question about Interfaces, can someone explain the concept of Interfaces in Java to me?
i just knew that it can be used to replace the Multiple Inheritance, but how it works?

thank you

 

[Iron_Cross]

An interface is just a set of methods. You use it, so that you can know a certain object contains a certain set of methods without having to know the object. And yes, it's used in multiple instead of multiple inheritence.

 

[ZoneFire]

oh..thanks
but then, how we can implement interface in our program?
how both of them are related?

thank you

 

[Iron_Cross]

Say I have an interface named MyInterface which contains two methods doSomething() and doSomethingElse() I would create the interface like this

public interface MyInterface{
    void doSomething();
    void doSomethingElse();
}

Then I'd use it like this

public class SomeClass implements MyInterface{
    public void doSomething(){
         // do some work
    }

    public void doSomethingElse(){
        // do some work here too
    }

    //
    // Anything else I want this class to have can go here
    //
}

Then to actually use that class I'd do something like

public class SomeOtherClass{
     public static void main(String[] args){
          // I can either use a direct instantiation like this
          SomeClass obj = new SomeClass();
          obj.doSomething();
          // When using direct instantiation I have direct access to
          // everything that class has to offer, all methods (non private)
          // all fields (non private) and so on and so forth

          // Or I can use indirect instantiaion
          MyInterface obj = new SomeClass();
          obj.doSomethingElse();
          // now I only have access to the interface methods
    }
}

Interfaces are good with multiple inheritence, abstraction, and reflection. Hope this clarifies it a bit. Oh, and you can use as many interfaces as you like, just separate them by commas.

 

[ZoneFire]

wow, it is really nice...
the explanation is clear and understandable
now, i can grab the concept of interfaces in Java.
thanks a lot, Iron_Cross