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Help a beginner with Java

Discussion in 'Programming & Webmastering' started by razaron, Jul 5, 2011.

  1. streetfighter 2

    streetfighter 2 New Member

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    That isn't how you declare a while loop.

    That's a for loop declaration.

    It should be:
    Code:
    [B]for[/B] (int i = 0; i < 25; i++){
    It's a very common mistake, don't feel bad about it.
    Last edited: Sep 5, 2011
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  2. razaron

    razaron

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    :banghead: I feel like crying in the corner now.

    Edit: but a stupid one none the less. Seeing as I've used it correctly several times before.
  3. caleb

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    Maybe use FOR instead of WHILE :)
    razaron says thanks.
  4. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    Good job on the game :toast:

    The next logical step would be to make the game more complex.
    For instance, instead of just having the target be X distance away, give it a left and right position so that the player has to enter the angle to turn also (Power=10, Angle=25, 30° to the left).
    If the player misses, have the target advance and moves left or right toward him some random amount before the next shot. If the target reaches the player, the player "dies".
    See if the player gets the target or the target gets the player (call it a zombie instead of a "target" :D )

    Then ... add multiple zombies attacking.

    Also, I saw your comment about methods returning void (or nothing).
    This means it returns no value to whatever called it. You will also get an error if you try to get a return value from a void method.
    Code:
    void MyMethod()
    {
        // Do something, but return nothing.
    }
    
    int test = MyMethod() <-- Error
    
    However, if a method returns a value, you do not have to use it if you do not need what it returns.
    Last edited: Sep 5, 2011
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  5. razaron

    razaron

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    So a void method is like a bully?
    "What's yours is mine and what's mine is also mine.", said the void method to the other methods.
  6. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    Another thing to keep in mind, as I stated above, is that when you look at code just because a method call does not use it's return value, does not mean it does not return anything.

    For instance, the Show method of the MessageBox class in C# returns a value of type DialogResult. If you don't care what that value is, you can call the method and just let it pitch the result or use it if you need it.
    Code:
    MessageBox.Show("Text for messgae box"); // Don't need result
    
    or
    
    DialogResult MyResult = MessageBox.Show("Text for message box"); // Save result for later
    
    A void method isn't a bully, it's just so broke it can't afford to give anything back :D


    Also, Java is not dead. It's used by a lot of people for it's cross-platform capabilities.
    for instance, Minecraft is written in Java.
    Last edited: Sep 5, 2011
  7. human_error

    human_error

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    That's why a large number of corporations have programs written in Java (some of these programs make billions each year in revenue)? Java is hardly dead, and it isn't going to be going away for a looong time.

    As for what to develop next Kreij is right - it is much better to improve on and add to an existing program if you want to try more complex things, at least until you can't think of any more ways to add to it.
    Last edited: Sep 5, 2011
  8. razaron

    razaron

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    Currently I'm going through the different kind of data structures (array, bitset etc.). After that I'm going to learn basic swing and remake "Fate/stay night" with place-holders for all the audio, text and images. That ought to help in getting used to the syntax.
  9. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    When learning the different data structures, take the time to learn not only how they work but where they are a "best fit".

    If you need a data structure to hold a bunch of strings you could use an array, but depending upon what you are doing (like maybe adding and remove them) a List of string may be more appropriate because it will execute faster and is inherently dynamic in size.

    You mean after writing your first "Hello World" program you should not jump right into making a 3D shooter? :laugh:
    razaron says thanks.
  10. streetfighter 2

    streetfighter 2 New Member

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    No offense good sir, but I've seen your posts: you do not know that much about programming.
    It should be noted that void methods can still modify variables, whether globals, class members or certain types of passed objects (similar to python). This gets confusing so check this out:
    http://www.javaworld.com/javaworld/javaqa/2000-05/03-qa-0526-pass.html

    Java doesn't support void type variables (AFAIK) but other languages do. For instance I wanted a function to retrieve private variables from a class instance in C++. The traditional way to do this is with a template, which is a type of generic specific to C++. (Java [J2SE 5.0+] also supports generics.) I intend to create a generic but for now I'm prototyping the behavior using void:
    PHP:
    //Exposes private variable values
    //note: might want to change this to BOOL in case name detection fails
    //warning: this is not production quality code, it's for debugging only
    void ProfileControl::request(void* var, LPCTSTR name) {
        if (
    _tcscmp(name,_T("settings"))==0){
            
    unsigned chartSettings=(unsigned char*)var;
            *
    tSettings=settings;
        }
        else if (
    _tcscmp(name,_T("profilesSaved"))==0) {
            
    vector<wstring>* tProfilesSaved=(vector<wstring>*)var;
            *
    tProfilesSaved=profilesSaved;
        }
        else if (
    _tcscmp(name,_T("szDir"))==0) {
            
    TCHARtszDir=(TCHAR*)var;
            
    _tcscpy(tszDirszDir);
        }
        else if (
    _tcscmp(name,_T("find"))==0) {
            
    wstringtProfile=(wstring*)var;
            
    wstring profile;
            if (
    findprofile(*tProfile, &profile)) {
                *
    tProfile profile;
            } else {
                *
    tProfile _T("");
            }
        }
        return;
    }
    What that function does is allow you to pass in a variable of several different types, then request a variable by name and retrieve the desired value from the object instance. It would be invoked like this:
    PHP:
    TCHAR szDir[MAX_PATH];
    tProfileControl->request(szDir,_T("szDir"));
    It also uses loads of pointers which Java doesn't support . . .

    NOTE: I'm using php tags for syntax highlighting, the code is written in C++.
    Not only that, but if razaron learns how to build his own data structures he can fit data structures to code rather than fit code to data structures. I'm pretty sure that sounds more confusing than I want it to be.
    Last edited: Sep 5, 2011
  11. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    We may want to give raz a little time to let the basics sink in before we give him an aneurysm trying to figure out delegates, generics, llambda expressions, etc. :D
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  12. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    Keep it on topic. He asked for help with Java, not for personal opinions on the merits of any particular programming language. Posts removed.
    Aleksander and razaron say thanks.
  13. Aleksander

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    Ok, sorry for the other post, but anyway i don't know why none suggested any videos
    http://www.youtube.com/watch?v=Hl-zzrqQoSE
    Thenewboston is well known for teaching
    If i was you i would learn all the videos than come here again after learning that much
    @streetfighter 2
    I have not seen a program like the one in my signature.... yet
    Last edited: Sep 5, 2011
    razaron says thanks.
  14. razaron

    razaron

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    [figured it out]
    Last edited: Sep 25, 2011
  15. razaron

    razaron

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    This results in a stackoverflow error.
    If I remove " && halffact1==0.75 && halffact2==0.75 && halffact3==0.75" from the "checkGrid()" method then it results in an array full of zeros.
    What am I doing wrong?
    Code:
    import java.util.*;
    
    public class test{
    	static Random rand = new Random();
    	
    	public static void main(String args[]){
    		print(secondaryGrid());
    	}
    	
    	
    	//prints MD array
    	public static void print(int[][] x){
    		for(int j=0;j<3;j++){
    			for(int i=0;i<3;i++){
    				System.out.print(x[i][j]+" ");
    			}
    			System.out.println();
    		}
    	}
    	
    	
    	//makes the permutation of numbers 1-3
    	public static int[] getPerm(){
    		int[] temp = {1,2,3};
    		int[] perm = new int[3];
    		int sum = 0;
    		
    		do{
    			for(int i=0;i<3;i++){
    				int r = rand.nextInt(3-i);
    				perm[i] = temp[r];
    				temp[r] = temp[2-i];
    				sum += perm[i];
    			}
    		}while(sum != 6);
    		return perm;
    	}
    	
    	
    	//sets up the rows in a primary grid with previously made permutations
    	public static int[][] primaryGrid(){
    		int[][] primaryGrid = new int[3][3];
    		int[] row1 = getPerm();
    		int[] row2 = getPerm();
    		int[] row3 = getPerm();
    		
    		for(int i=0;i<3;i++){
    			primaryGrid[i][0] = row1[i];
    			primaryGrid[i][1] = row2[i];
    			primaryGrid[i][2] = row3[i];
    		}
    		return primaryGrid;
    	}
    	
    	
    	//returns a secondary grid based of the primary grid, if checkGrid is true.
    	public static int[][] secondaryGrid(){
    		int[][] primaryGrid = primaryGrid();
    		int[][] secondaryGrid = new int[3][3];
    		
    		if(checkGrid(primaryGrid)==true)
    			secondaryGrid = primaryGrid;
    		else
    			secondaryGrid();
    		
    		return secondaryGrid;
    	}
    	
    	
    	//sets and returns the boolean value, checkGrid, based on the columns of a grid
    	public static boolean checkGrid(int[][] x){
    		int sum1 = 0;
    		int sum2 = 0;
    		int sum3 = 0;
    		int fact1 = 1;
    		int fact2 = 1;
    		int fact3 = 1;
    		double halffact1 = 1;
    		double halffact2 = 1;
    		double halffact3 = 1;
    		
    		boolean checkGrid = false;
    		
    		for(int i=0;i<3;i++){
    			//sums
    			sum1 += x[0][i];
    			sum2 += x[1][i];
    			sum3 += x[2][i];
    			//factorial
    			fact1 *= x[0][i];
    			fact2 *= x[1][i];
    			fact3 *= x[2][i];
    			//halved factorials
    			halffact1 *= (double)(x[0][i]/2);
    			halffact2 *= (double)(x[1][i]/2);
    			halffact3 *= (double)(x[2][i]/2);
    		}
    		
    		if(sum1==6 && sum2==6 && sum3==6 && fact1==6 && fact2==6 && fact3==6 && halffact1==0.75 && halffact2==0.75 && halffact3==0.75)
    			checkGrid = true;
    		else
    			checkGrid = false;
    		
    		return checkGrid;
    	}
    	
    }
  16. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    I'm not sure but it looks like the checkGrid method is returning itself (which would cause a stack overflow because you are not specifying that it return the local boolean variable by the same name (this.checkGrid).
  17. razaron

    razaron

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    To call a method in Java you must have "()" at the end of the name even if there are no parameters.
    Today is not your day, lol.

    EDIT: The method checkGrid() returns a boolean named checkGrid, the method primaryGrid() returns an array named primaryGrid and the method secondaryGrid() returns an array called secondaryGrid. I realize this is confusing. That's just how I like it...
    Last edited: Sep 25, 2011
  18. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    You are right. Today has not been my best day. lol
    Oh well, it's not the first time.

    I know you need to include the parenthesis when calling a method, but I was thinking that when you return checkGrid (without the parenthesis) it may be returning a pointer to the method instead of the value of the local checkGrid variable.

    I probably just need some sleep so I can once again seperate different programming language syntax in real time. :roll:

    Code:
    private static protected const internal void **string MyMethod (string *$lolwut)
    {
       10 : return ***this.MyMethod->&MyMethod (&(LPTRSTR)(@"Just kill me now"));
       goto: 10;
    }
    
    Last edited: Sep 26, 2011
  19. razaron

    razaron

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    I took the recursion out of the secondaryGrid() method and moved the double casts (in the checkGrid() method) into the brackets. It now works perfectly.
  20. razaron

    razaron

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    I have a really weird problem.
    This works,
    PHP:
    long time getTime();
    double theta = (360*time)/1000;
    long x = (long)(100 Math.cos(Math.toRadians(theta)));
    long y = (long)(100 Math.sin(Math.toRadians(theta)));
    but this doesn't,
    PHP:
    long time getTime()%1000;
    double theta 360*((time)/1000);
    long x = (long)(100 Math.cos(Math.toRadians(theta)));
    long y = (long)(100 Math.sin(Math.toRadians(theta)));
    This code is supposed to give the x,y co-ords of a dot thus animating it. getTime() returns a long value of time in milliseconds.
    The second piece of code is mathematically sound but doesn't work.
    Last edited: Oct 12, 2011
  21. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    Define "doesn't work".
  22. razaron

    razaron

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    One animates. The other just has a static image.
    I fiddled a bit more and figured out something even more weird. If for the second piece of code I make theta equal (360*time)/1000, it animates.
  23. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    The two code blocks you posted are not mathematically equivelant.
    I guess still an not sure how to respond.
  24. razaron

    razaron

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    The cosine and sine make them mathematically equivalent. The theta values are different but the cos(theta) and sin(theta) values are the same. Check it on a calculator.
    Also, 360 * (time/1000) == (360*time)/1000. Think of them as fractions.
    Last edited: Oct 13, 2011
  25. Aleksander

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    I think it is not a mathematical problem here.
    It is java which takes the time as another thing and an int as another.
    Probably you cannot divide time.
    Not that i know java though.

    Also, this 360 * (time/1000) == (360*time)/360 is not equal

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