Initializing variables

[memati bas]

Hi,
When I do not initialize the reference variable in the below codes, there are a compile time error occured.
the reference variable that I mention : IntBag b
So Why ??

 
import java.util.*;
public class Testing2 {
 
public static void main(String args[]){

Scanner scan = new Scanner(System.in);
int c1;
int num = 0;
IntBag b = new IntBag(8); // create a compile error if not initialize

 do{

System.out.println("1)Create a new empty set of values with a specified maximum capacity (any previous set of values is lost!)\n" 
+ "2)Read a set of values into the collection (use negative value to indicate the set has all been entered.)\n" + 
"3)Read a single test value.\n4)Compute the set of locations of the test value within the set of values* (see note below).\n5)Print the set of values." + 
"\n6)Print the set of locations. \n7)Add specified value to set of values at specified location " +
"\n8)Remove value at specified location from the set of values \n9)Quit the program.");
System.out.println("please enter your choice");
c1 = scan.nextInt();

if(c1 == 1){
System.out.println("please enter the maximum capacity");
int max = scan.nextInt();
b = new IntBag(max);
}
else if(c1 == 2){
int x;
for(int c = 0; c < b.bag.length; c++){
System.out.println("please enter the set of values");
x = scan.nextInt();
b.add2(x,c);
}
}
else if(c1 == 3){

System.out.println("please enter the test value");
num = scan.nextInt();
}
else if(c1 == 4){
b.set(num);
}
else if(c1 == 5){
for(int d = 0; d < b.valid; d++)
System.out.println(b.getValue(d));
}
else if(c1 == 6)
{
System.out.println(b.set(num));
}


else if(c1 == 7){
System.out.println("please enter a  value");
int m = scan.nextInt();
System.out.println("please enter the location");
int t = scan.nextInt();
b.add2(m,t);
}
else if(c1 == 8){
System.out.println("please enter the location of the value that" +
 " you remove");
int t = scan.nextInt();
b.remove(t);
}
else if(c1 == 9){
System.out.println("Thanks for using this program, Good Bye...");
}

 }while(c1 != 9);

}

}
 

[Dani Atrei]

The compile time errors just tells you that b may not have been initialised, this is to tell you that if you run the program there's likely going to be some problems because it's going to try calling a method with a null reference pointing nowhere, and hence won't work. There's no point compiling something that's not going to do what's intended.
[ February 05, 2006: Message edited by: Dani Atrei ]

[memati bas]

Hi,
I heard that Java does not automatically initialise local variables, though it will initialise any arrays or objects newly created to be stored in local variables. but the code that I sent deny this.
Why???

[Henry Wong]

Java does not automatically initialize local variables. I don't believe that there is an exception for arrays and objects.

Henry

[memati bas]

Originally posted by Henry Wong:
Java does not automatically initialize local variables. I don't believe that there is an exception for arrays and objects.

Henry

You should visit the following link.
http://mindprod.com/jgloss/initialisation.html

[Henry Wong]

Originally posted by memati bas:


You should visit the following link.
http://mindprod.com/jgloss/initialisation.html

The article did *not* say that arrays (that are local) will get automatically initialized. It mentioned that when you initialize the local array variable, Java will automatically initialize the elements, of that array.

Henry

[memati bas]

Oh, thanks for your reply.
Now , I kept the idea.

[Garrett Rowe]

Originally posted by memati bas:
Hi,
I heard that Java does not automatically initialise local variables, though it will initialise any arrays or objects newly created to be stored in local variables. but the code that I sent deny this.
Why???

In this case b is indeed a local variable (therefore not initialized to anything) and there is no "object newly created" hence the error.