Programming Forums > Application Development > Java

paulchwd · Apr 14th, 2007, 12:09 AM

Hi All,

This gives me a null pointer exception:

   System.out.println("\nThere are " + polyInstance.signChanges(tempCoefsArray,  noCoefs) + " positive real roots in the equation you entered\n");

......other non important code here.....

public int signChanges(String tempCoefsArray[], int noCoefs)
	{

		int signChanges=0;           
     
			for(int i=0; i<=tempCoefsArray.length-2; i++)
			{
                               if(tempCoefsArray[i].charAt(0) != tempCoefsArray[i+1].charAt(0))//null ptr here
				 {

					 signChanges++;
				 }
				
			}
		return signChanges;
	}

PhilBon · Apr 14th, 2007, 12:48 AM

I'm not sure if it is the same with Chars as it is with strings, but I know with strings, you have to do

(Toggle Plain Text)

tempCoefsArray[i].charAt(0).equals

or something like it. You have to have .equals (not sure about case) after the var, but with the .charAt, i'm not sure if it goes before or after.

titaniumdecoy · Apr 14th, 2007, 2:01 AM

@PhilBon: The OP is correctly comparing chars with the != operator; however you are correct that in most cases Strings should be compared with the equals method.

@paulchwd: It appears one of the elements in the tempCoefsArray is null. If you did not intend this to be the case you should review the code in which the argument is generated. However, if you accept the possibility that one of the elements of tempCoefsArray might be null, you should check for that before comparing each value.

Also, the second argument to the signChanges method is unused within the method, and if it represents what its name would indicate (the length of the array) the information it provides is redundant.

Apr 14th, 2007, 12:09 AM	#1
paulchwd Hobbyist Programmer Join Date: Mar 2005 Posts: 139 Rep Power: 4	String compare Hi All, This gives me a null pointer exception: (Toggle Plain Text) System.out.println("\nThere are " + polyInstance.signChanges(tempCoefsArray, noCoefs) + " positive real roots in the equation you entered\n"); ......other non important code here..... public int signChanges(String tempCoefsArray[], int noCoefs) { int signChanges=0; for(int i=0; i<=tempCoefsArray.length-2; i++) { if(tempCoefsArray[i].charAt(0) != tempCoefsArray[i+1].charAt(0))//null ptr here { signChanges++; } } return signChanges; } System.out.println("\nThere are " + polyInstance.signChanges(tempCoefsArray, noCoefs) + " positive real roots in the equation you entered\n"); ......other non important code here..... public int signChanges(String tempCoefsArray[], int noCoefs) { int signChanges=0; for(int i=0; i<=tempCoefsArray.length-2; i++) { if(tempCoefsArray[i].charAt(0) != tempCoefsArray[i+1].charAt(0))//null ptr here { signChanges++; } } return signChanges; } Last edited by paulchwd; Apr 14th, 2007 at 12:20 AM.

Apr 14th, 2007, 12:48 AM	#2
PhilBon Hobbyist Programmer Join Date: Nov 2005 Posts: 171 Rep Power: 3	I'm not sure if it is the same with Chars as it is with strings, but I know with strings, you have to do (Toggle Plain Text) tempCoefsArray[i].charAt(0).equals tempCoefsArray[i].charAt(0).equals or something like it. You have to have .equals (not sure about case) after the var, but with the .charAt, i'm not sure if it goes before or after.

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Apr 14th, 2007, 2:01 AM	#3
titaniumdecoy Expert Programmer Join Date: Nov 2005 Posts: 836 Rep Power: 3	@PhilBon: The OP is correctly comparing chars with the != operator; however you are correct that in most cases Strings should be compared with the equals method. @paulchwd: It appears one of the elements in the tempCoefsArray is null. If you did not intend this to be the case you should review the code in which the argument is generated. However, if you accept the possibility that one of the elements of tempCoefsArray might be null, you should check for that before comparing each value. Also, the second argument to the signChanges method is unused within the method, and if it represents what its name would indicate (the length of the array) the information it provides is redundant.

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Programming Forums > Application Development > Java

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