Programming Forums > Application Development > Java

Harakim · Jun 4th, 2006, 3:25 PM

When you are done with this, if you wouldn't mind sending me the code I'd like to look at it. I still think you should use Serialization. Since I can't compile it, I would probably write some buggy code.

titaniumdecoy · Jun 4th, 2006, 4:56 PM

Quote:

Originally Posted by Harakim

For one, I think this line of code:

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268:   tetPiece [pieceCounter].setFilledPiece (xLen, yLen, true);

will give a NullPointerException for reasons mentioned by TitaniumDecoy.

It was actually Arevos who mentioned that. :p

Eric the Red · Jun 4th, 2006, 7:13 PM

Another problem in my code is that I'm not able to send array information between classes. I've created a sample program: Would anyone be able to fix this program so that it actually returns the array?

In c++, I would just send a pointers/refferencea to my array and into the class method. In java is there anyway I can have a pointer to my array in ArrayCollect, and bring that pointer into ArrayData. Or does this work with by fixing the syntax errors?

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 Edit**
class ArrayData
{
    int someInt [] = new int [1];

    public ArrayData ()
    {
        someInt = new int [3];

        for (int i = 0 ; i < 3 ; i++)
        {
            someInt [i] = (5 * i) + 1;
        }
    }


    int getInt ()
    {
        return someInt [];
    }
}
class ArrayCollect
{
    public static void main (String [] arguments)
    {
        ArrayData tempData = new ArrayData ();
        int yeint[] = new int[3];
       yeint[] = tempData.getInt ();
  
    }
}

xavier · Jun 4th, 2006, 10:51 PM

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int getInt ()
    {
        return someInt ;
    }

That should do it.

Arevos · Jun 5th, 2006, 3:59 AM

Small correction:

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int[] getInt()
{
    return someInt;
}

xavier · Jun 5th, 2006, 5:19 AM

Thanks Arevos, I should pay more attention damnit.

Eric the Red · Jun 5th, 2006, 8:17 PM

Thanks for all your help. Somethings in my mind though: In c++ you can pass pointers and refferences into a funtion. So in java is there any simple way to do this? I searched the forums and found "event methods", wow I don't want to get into that. Therefore, this can't be done as it can in c++ can it (create a refference to an object)?

Here's a little example I Found.

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#include <iostream>
 #include <stdlib.h>
 

 void swap(int &x, int &y);

 

 int main()

 {

     int x = 5, y = 10;

 

     std::cout << "Main. Before swap, x: " << x 

                                 << " y: " << y << "\n";

     swap(x,y);

     std::cout << "Main. After swap, x: " << x 

                                << " y: " << y << "\n \n \n";
                                
    int x2 = 30, y2 = 40;
    std::cout << "Main. Before swap, x: " << x2 

                                 << " y: " << y2 << "\n";

     swap(x2,y2);

     std::cout << "Main. After swap, x: " << x2 

                                << " y: " << y2 << "\n";
    system("Pause");

     return 0;

 }

 

 void swap (int &rx, int &ry)

 {

     int temp;

 

     std::cout << "Swap. Before swap, rx: " << rx 

                                 << " ry: " << ry << "\n";

 

     temp = rx;

     rx = ry;

     ry = temp;

 

     std::cout << "Swap. After swap, rx: " << rx 

                                << " ry: " << ry << "\n";


 }

Quote:

Source: "Sam's teach yourself c++" by Jesse Liberty

And if the answer is "No java can't do that", wow i'm in a state of shock.

Now back to finishing this tetris game.

Harakim · Jun 6th, 2006, 1:12 AM

This is a horribly complicated subject for me to explain, but I'll try.

If I understand you correctly, you want to pass the array and modify it and not have to return it. In Java, you can do this the same way as C++.

The references/pointers you pass in Java/C++ pass by value. They are numbers.

Just for sake of an example:

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char *temp = new char[x];
foo( temp );

void foo( char *ptr )
{
	ptr = new char[y];
}

`temp` still points at "new char[x]". Why?
I'll just show you a simplified example with sample addresses. It would probably help if you kept track on paper.

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char *temp;

temp is created at location 0x00

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temp = new char[x];

a new array is allocated starting at location 0x10
the value of the array's address (0x10) is stored in 0x00 (temp)

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foo( temp );

`ptr` is created at location 0x04

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ptr = new char[y];

a new array is allocated starting at location 0x20
the value of the array's address (0x20) is stored in 0x04 (ptr)

The chart would look like this:
location value
0x00 0x10
0x04 0x20
0x10 the value of temp[0]
0x20 the value of ptr[0]

Put another way, it is like saying this:
int temp = 1;
int ptr = temp;
ptr = 100;

Temp won't change, just ptr. char * is just an int that holds a memory address. (on 32-bit machines)

Eric the Red · Jun 6th, 2006, 1:47 AM

Thanks.. my book doesn't cover any of that stuff (Sam's Java Programming in 24 Hours). I'm definately out to get a book tonight.

Great explanation!

tumbleTetris · Jun 6th, 2006, 5:09 AM

lol yeah, sams 24 hour books have a bad reputation...

all that stuff *should* be explained in any book claiming to teah java progamming.

Jun 4th, 2006, 7:13 PM	#13
Eric the Red Hobbyist Programmer Join Date: Feb 2006 Posts: 214 Rep Power: 0	another error from code Another problem in my code is that I'm not able to send array information between classes. I've created a sample program: Would anyone be able to fix this program so that it actually returns the array? In c++, I would just send a pointers/refferencea to my array and into the class method. In java is there anyway I can have a pointer to my array in ArrayCollect, and bring that pointer into ArrayData. Or does this work with by fixing the syntax errors? (Toggle Plain Text) Edit** class ArrayData { int someInt [] = new int [1]; public ArrayData () { someInt = new int [3]; for (int i = 0 ; i < 3 ; i++) { someInt [i] = (5 * i) + 1; } } int getInt () { return someInt []; } } class ArrayCollect { public static void main (String [] arguments) { ArrayData tempData = new ArrayData (); int yeint[] = new int[3]; yeint[] = tempData.getInt (); } } Edit** class ArrayData { int someInt [] = new int [1]; public ArrayData () { someInt = new int [3]; for (int i = 0 ; i < 3 ; i++) { someInt [i] = (5 * i) + 1; } } int getInt () { return someInt []; } } class ArrayCollect { public static void main (String [] arguments) { ArrayData tempData = new ArrayData (); int yeint[] = new int[3]; yeint[] = tempData.getInt (); } } __________________ Death smiles at us all. All a man can do is smile back.

Jun 4th, 2006, 10:51 PM	#14
xavier Professional Programmer Join Date: Oct 2004 Location: .ro Posts: 383 Rep Power: 4	(Toggle Plain Text) int getInt () { return someInt ; } int getInt () { return someInt ; } That should do it. __________________ Don't take life too seriously, it's not permanent !

Jun 5th, 2006, 3:59 AM	#15
Arevos Programming Guru Join Date: Aug 2005 Location: England Posts: 1,499 Rep Power: 5	Small correction: (Toggle Plain Text) int[] getInt() { return someInt; } int[] getInt() { return someInt; }

Jun 5th, 2006, 5:19 AM	#16
xavier Professional Programmer Join Date: Oct 2004 Location: .ro Posts: 383 Rep Power: 4	Thanks Arevos, I should pay more attention damnit. __________________ Don't take life too seriously, it's not permanent !

Jun 6th, 2006, 1:12 AM	#18
Harakim Hobbyist Programmer Join Date: May 2006 Location: West Jordan, Utah, United States Posts: 176 Rep Power: 3	This is a horribly complicated subject for me to explain, but I'll try. If I understand you correctly, you want to pass the array and modify it and not have to return it. In Java, you can do this the same way as C++. The references/pointers you pass in Java/C++ pass by value. They are numbers. Just for sake of an example: (Toggle Plain Text) char temp = new char[x]; foo( temp ); void foo( char ptr ) { ptr = new char[y]; } char temp = new char[x]; foo( temp ); void foo( char ptr ) { ptr = new char[y]; } `temp` still points at "new char[x]". Why? I'll just show you a simplified example with sample addresses. It would probably help if you kept track on paper. (Toggle Plain Text) char temp; char temp; temp is created at location 0x00 (Toggle Plain Text) temp = new char[x]; temp = new char[x]; a new array is allocated starting at location 0x10 the value of the array's address (0x10) is stored in 0x00 (temp) (Toggle Plain Text) foo( temp ); foo( temp ); `ptr` is created at location 0x04 (Toggle Plain Text) ptr = new char[y]; ptr = new char[y]; a new array is allocated starting at location 0x20 the value of the array's address (0x20) is stored in 0x04 (ptr) The chart would look like this: location value 0x00 0x10 0x04 0x20 0x10 the value of temp[0] 0x20 the value of ptr[0] Put another way, it is like saying this: int temp = 1; int ptr = temp; ptr = 100; Temp won't change, just ptr. char * is just an int that holds a memory address. (on 32-bit machines)

Jun 4th, 2006, 3:25 PM	#11
Harakim Hobbyist Programmer Join Date: May 2006 Location: West Jordan, Utah, United States Posts: 176 Rep Power: 3	When you are done with this, if you wouldn't mind sending me the code I'd like to look at it. I still think you should use Serialization. Since I can't compile it, I would probably write some buggy code.

Jun 6th, 2006, 1:47 AM	#19
Eric the Red Hobbyist Programmer Join Date: Feb 2006 Posts: 214 Rep Power: 0	Thanks.. my book doesn't cover any of that stuff (Sam's Java Programming in 24 Hours). I'm definately out to get a book tonight. Great explanation! __________________ Death smiles at us all. All a man can do is smile back.

Jun 6th, 2006, 5:09 AM	#20
tumbleTetris Programmer Join Date: May 2006 Posts: 39 Rep Power: 0	lol yeah, sams 24 hour books have a bad reputation... all that stuff should be explained in any book claiming to teah java progamming.

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Programming Forums > Application Development > Java

Working with objects