Chap 1 ex 6 K&B (varargs)

[Mohan Dinesh Ganti]

Hi guys,

my issues seem to be ignored all the time but I am anyway going to write again hoping to get some response.

In the K&B book, chapter 1, exercise 6 it is asked if, considering the following calls

doStuff(1);
doStuff(1,2);

which possible method signatures for doStuff are possible. In the list of options there is also

static void doStuff(int[] doArgs)

That is not considered a valid response but I tested it and it works.

what do you think?

Thanks,

Mohan

[Edisandro Bessa]

Hi Mohan,

Are you sure the code compiles ? I think you are using a previous valid version of .class file.

I tried the following code and it doesn't compile.

 
class Voop {
    public static void main(String[] args) {
    doStuff(1);   [B] //1 [/B]
    doStuff(1,2); [B] //2[/B]
 
    }
    
    static void doStuff(int[] doArgs) { }
}

I get the following error at both lines 1 and 2, respectively

doStuff(int[]) in Voop cannot be applied to (int)

doStuff(int[]) in Voop cannot be applied to (int,int)

[Garrett Rowe]

What does your test program look like. This code resulted in a compiler error on my machine.

public class VarargsTest
{
   public static void main(String[] args)
   {
      int result = doStuff(1, 2, 3, 4, 5);
 
      System.out.println(result);
   }
 
   public static int doStuff(int[] nums)
   {
      int sum = 0;
 
      for (int e : nums)
      {
         sum += e;
      }
 
      return sum;
   }
}

the error was:

C:\Documents and Settings\Garrett Rowe\My Documents\My Java Stuff\MiscTestClasses\VarargsTest.java:5:
 doStuff(int[]) in VarargsTest cannot be applied to (int,int,int,int,int)
      int result = doStuff(1, 2, 3, 4, 5);
                   ^
1 error
 
Tool completed with exit code 1

[ March 24, 2006: Message edited by: Garrett Rowe ]

[Mohan Dinesh Ganti]

Thanks guys,

actually you are right, I don't know how but I got confused and tested the opposite scenario

class vararg
{
public static void main(String[] args)
{
int[] b = {1,2,3};
test(b);
}

void test (int... x)
{
for (int a:x)
System.out.println(a);
}
}

which of course worked :-)

Mohan

[Mohan Dinesh Ganti]

Of course it worked with static added to the test method ;-)

Mohan

[Edisandro Bessa]

Hi Mohan,

Recently I got a question from Whizlabs simulator something like that.

Please let me use your code as example ok ?

class vararg{
    public static void main(String[] args){
        int[] b = {1,2,3};
        test(b);
    }
    
    public static void test (int[] x){
        System.out.println("int[]");
    }
    
    public static void test (int... x){
        System.out.println("int ...");    
    }
}

What is the result of preceeding code ?

a)int[]
b)int ...
c)compilation fails
d)no output at runtime
e)runtime error

At a first look I tended to choose (a) once I am sending an int array and there's a corresponding method to call.

But, for my surprising the code doesn't compile.

To compiler both test method definitions are the same. Very interesting.

[mambe nanje]

but it is suppose to compile since the jvm refers to all methods be4it can consider varargs so I guess it is suppose to print int[]

[Mohan Dinesh Ganti]

Yes, it's interesting to know.. you never know what the exam will ask ;-)

Thansk for sharing your experiment,

Mohan

[Edisandro Bessa]

After practice a few examples about varargs I could figure out the following rules :

Arrays can be passed to methods which signature have either array types or varargs types.

Code Sample :

int [] a = {1,2,3,4,5}

Method with both signatures int[] or int ... are able to receive this array as argument.

Primitive types can be passed only to methods which signature is fixed or primitive variable-length

Code Sample

doStuff(1,2,3);

Can be passed to either methods with signature int x, int y, int z or int ...

Methods with int[] signature are not able to receive primitive varargs.