how to call method?

[leapinlizard]

I'm getting error I don't know how to call this method here in test file
error: Exception in thread "main" java.lang.NullPointerException
at BookTest.printReport(BookTest.java.39)
at BookTest.main(BookTest.java:17)

my code

public class BookTest
{

        static Book bookArray[] = new Book[4]; 
	static String dataArray[][] = new String[4][8];
		
	public static void main(String args[])

	{
              
		buildInstances();
		printReport();                
              
	}

	public static void buildInstances()
	{

	 	 String dataArray [][] = {{"Where's my car", "Aston Kutcher","777","ORiely","Dallas","5.95","Fiction","123","456"},
					 {"Earthquakes","ChuckBerry","435","LABooks","LA","75.00","NonFiction"},
					 {"Doom","The Rock","918","Sans Publishing","LA","12.50","Fiction","1233","2323"}, 
					 {"Universal Studios","Walt","987","Dell","Houston","29.90","NonFiction"}};
	 
	}//build instances


	public static void printReport()
	{ //print report

               for (int i=0; i<bookArray.length; i++)
                {

                	
 			if (dataArray[i][6].equals("Fiction"))

                   	    bookArray[i]=new Fiction (dataArray[i][0],dataArray[i][1], Integer.parseInt(dataArray[i][2]), new Publisher(dataArray[i][3],dataArray[i][4]), Double.parseDouble(dataArray[i][5]),i, new Background(Integer.parseInt(dataArray[i][7]), dataArray[i][8]));
		
	
                         
			if (dataArray[i][6].equals("NonFiction"))
                            bookArray[i]= new NonFiction(dataArray[i][0],dataArray[i][1], Integer.parseInt(dataArray[i][2]), new Publisher(dataArray[i][3],dataArray[i][4]), Double.parseDouble(dataArray[i][5]),"History");
		

	
                                                       
	           		
		}// end of FOR Loop


            
         	
                for (int j=0; j<4;j++)
                    {
                     bookArray[j].calculateTotalCharge(Double.parseDouble(dataArray[j][5])+2*3);                
                     System.out.println();
		     System.out.println();

		    
			System.out.printf(bookArray[j].toString());
			
                    } //end of for with j  

 		}///print report 	               





   //  } //end of main


} //end class BookTest

[Fubarable]

Which line above throws the error? There's an object on that line that has not been initialized, that is null, and you are trying to use it.

Incidentally, I know which line and object is causing the problem, but if you answer my questions, myself or one the others here will try to help you learn how to solve these errors on your own.

Best of luck.

[Fubarable]

Also, to help you figure this out more, please look at this simple program:

public class MyClass
{
  static int value = 0;
  
  public static void setValueTo3()
  {
    int value = 3;
  }
  
  public static void main(String[] args)
  {
    setValueTo3();
    System.out.println(value);
  }
}

Run this program if you can. What will the println in the main method show, 3 or 0?

So why doesn't it show 3 even though the program sets value to 3 in the setValueTo3() method? The reason is that the value variable in this method is not the same as the one declared in the class. It is a completely separate and independent variable since it has been re-declared.

This re-declares the variable:

  public static void setValueTo3()
  {
    int value = 3; // this is a re-declared value variable
  }

If I want to set the class's value variable, I use the variable in the method above, but I don't declare it. This is the right way to code the method:

  public static void setValueTo3()
  {
    // there is no "int" in front of the variable here so it
    // is not redeclared
    value = 3; // this changes the class's value variable
  }

You do something similar in your program. Do you see where?

[leapinlizard]

ok I got your point but still i'm getting error

public class examp
{

		static String bookArray[] = new String[5];
		static String dataArray[][];

	public static void main(String args[])
	{
		buildInstances();
		
		 printReport();
		


	 }//main

		public static void buildInstances()
		{	

		   dataArray[][] ={{"HELLO"," MY NAME"," IS"," Alex"," king","jadu"},
				  {"HELLO"," THIS IS"," SE"," LIN"," SECOND","jadu"},
				  {"HELLO"," DO U ST"," LL"," REM"," EMBER ","jadu"},
				  {"HELLO"," 4TH LIN"," IN"," PRO"," GRESS ","jadu"},
				  {"HELLO"," DOWNTOW"," N "," HUH"," HELLO ","jadu"}};

		}
					

		public static void printReport()
		{
		
		for (int i=0; i<bookArray.length; i++)
		{
		   System.out.println(dataArray[i][0]+dataArray[i][1]+dataArray[i][2]+dataArray[i][3]+dataArray[i][4]+dataArray[i][5]);

	
		}

		}//print report
}

[markw8500]

That is my fault... You need to declair dataArray[][] before you fill it with your values... (I advised it in leapinlizard's other post)

[Fubarable]

Not the same error though. You're finding one of Java's quirks. You can initialize an array as you're doing it, only at declaration.

In other words, if you declare the array somewhere:

// array's declared here
static String dataArray[][];

then you can't initialize it somewhere else like this:

       dataArray[][] ={{"HELLO"," MY NAME"," IS"," Alex"," king","jadu"},
          {"HELLO"," THIS IS"," SE"," LIN"," SECOND","jadu"},
          {"HELLO"," DO U ST"," LL"," REM"," EMBER ","jadu"},
          {"HELLO"," 4TH LIN"," IN"," PRO"," GRESS ","jadu"},
          {"HELLO"," DOWNTOW"," N "," HUH"," HELLO ","jadu"}};

[leapinlizard]

for e.g.?

[code]

static String dataArray[][] = new String [5][5]; ????

[markw8500]

well I'm off the hook...

[Fubarable]

This could work,

  public static void buildInstances()
  {

    String[][] fooArray =
    {
      {"HELLO", " MY NAME", " IS", " Alex", " king", "jadu"},
      {"HELLO", " THIS IS", " SE", " LIN", " SECOND", "jadu"},
      {"HELLO", " DO U ST", " LL", " REM", " EMBER ", "jadu"},
      {"HELLO", " 4TH LIN", " IN", " PRO", " GRESS ", "jadu"},
      {"HELLO", " DOWNTOW", " N ", " HUH", " HELLO ", "jadu"}
    };

    // this will work if you're not using jagged arrays
    dataArray = new String[fooArray.length][fooArray[0].length];

    for (int i = 0; i < fooArray.length; i++)
    {
      for (int j = 0; j < fooArray[i].length; j++)
      {
        dataArray[i][j] = fooArray[i][j];
      }
    }
  }

but only if the arrays are not jagged -- that is all of the "inner" arrays have the same length, and that's not the case in your original program. For that you'll have to initialize your array like so:

    dataArray = new String[fooArray.length][];

    for (int i = 0; i < fooArray.length; i++)
    {
      dataArray[i] = new String[fooArray[i].length];
      for (int j = 0; j < fooArray[i].length; j++)
      {
        dataArray[i][j] = fooArray[i][j];
      }
    }

[Fubarable]

well I'm off the hook...

LOL!

No, I think it's going to take a combined effort here. Seriously, to the original poster, please speak to your instructor without delay and set up some tutoring. You've got some catching up to do it seems, and face-to-fact tutoring will offer the best chances of successfully doing this.