Hey Ankit,
Try the following code.

public class SumOfSeries3 {

/**
* @param 'series' holds the series need to be printed
*/
StringBuffer series = new StringBuffer();
public static void main(String[] args) {
SumOfSeries3 obj = new SumOfSeries3();
int start = 0;
int end = 7;
int result = obj.performOperation(start, end);
obj.modifySeries();
System.out.println(""+obj.series+result);
}

/**
* @param 'j' is used to know whether a no. is odd or even.
* @param 'evenNums' holds all the even numbers (i.e., all the negative numbers)
* @param 'oddNums' holds all the odd numbers (i.e., all the positive numbers)
*/
public int performOperation(int begin,int end){
int firstNumOfSeries = (begin*begin)+1;
int oddNums = firstNumOfSeries;
int evenNums = 0;
int temp = 0;
int j = 0;
series.append(firstNumOfSeries).append('-');
for(int i=begin+1;i<=end;i++){
temp = (i*i)+1;
series = series.append(temp);
if(j%2 == 0){
evenNums = evenNums + temp;
series.append('+');
}else{
oddNums = oddNums + temp;
series.append('-');
}
j++;
}
return(oddNums - evenNums);
}
/**
* This method modifies the series that need to be printed
* by replacing the last character of the String Buffer '+' with '='
*/
public void modifySeries(){
int length = series.length();
series.deleteCharAt(length-1);
series.append('=');
}
}
-------------------
o/p:
1-2+5-10+17-26+37-50=-28

Regards,
javaquest2010