Overloading For int and long ????

[RAGU KANNAN]

Hello,

I couldn�t find the different between example 1 and 2.
But the example 1 complies and run�s fine but the example 2 gives compilation error. I would like to know what is happening???

Thanks, Raghu.K

Error message of Example 2:-
C:\java>javac Test.java
Test.java:14: reference to getVal is ambiguous, both method getVal(int,int) in Base and method getVal(long,long) in Derived match
System.out.println(d.getVal(10, 7));

   
[B]Example 1:-[/B]
class A {
int increment(int x) {
return x + 10;
}
long increment(long x) {
return x + 20;
}
}
 
class B extends A {
 
static public void main(String[] args) {
A a = new A();
int y = a.increment(12);
System.out.println("Int  Y   " + y);
}
}
 
[B]Example 2:-[/B]
class Base {
public int getVal(int a, int b) {
return a - b;
}
}
class Derived extends Base {
public long getVal(long a, long b) {
return a + b;
}
}
class Test {
public static void main(String args[]) {
Derived d = new Derived();
System.out.println(d.getVal(10, 7));
}
}

[wise owen]

No compilation error for me. Output "3".

[Surendra Kumar]

I tried your Example 2, and I got output of 3 without any errors/exceptions.

[Nathaniel Stoddard]

When you have a literal number in your source code, it's an int. You can see below how to have a literal long.

int a = 12;
long b = 12L;

Here's the kicker: while polymorphism (overriding methods) is done during runtime, overloading is done at compile time. Therefore, whatever your variable is typed as will determine which method is run. Since your literal is an int, it calls the int-overloaded method. You can cast it as a long if you'd like to get the long-overloaded method.

This is best illustrated when you have a null value, but want to invoke a specifically-overloaded method. (Which isn't really the best design-wise, but oh well.)

import java.util.Date;
 
public class Test {
    public static void main(String[] args) {
        invoke(null);
    }
    
    private static void invoke(String v) {
        System.out.println("String");
    }
    
    private static void invoke(Date v) {
        System.out.println("Date");
    }
}

You should get a compile-time error saying the call to invoke is ambiguous. There's no type associated with a null value, so it doesn't know which method to call (a static, compile-time problem).

Fix this by casting the null value to either String or Date.

import java.util.Date;
 
public class Test {
    public static void main(String[] args) {
        invoke((String) null);
    }
    
    private static void invoke(String v) {
        System.out.println("String");
    }
    
    private static void invoke(Date v) {
        System.out.println("Date");
    }
}

[RAGU KANNAN]

Hello Wise and Sundar,

Which version you guy's are trying, I am using 1.4 and These are the errorme message i got when i compile

Thanks, Raghu.K

    
 
C:\java>javac Test.java
Test.java:14: reference to getVal is ambiguous, both method getVal(int,int) in Base and method getVal(long,long) in Derived match
                   System.out.println(d.getVal 10,7));
                                       ^
1 error   

[Surendra Kumar]

I tried with Java 1.5 from eclipse IDE, and with 1.4 from a command line.
Both worked fine with output of 3.

[Gizp Potts]

I tried with Java 1.5 and the program compiles and gives an output of 3