I am doing an assignment for which I am forced to store data of an unknown type in an array, and interact with that array. I am testing my code and am getting a null pointer exception when I try to add the first value to the array. The value should be null, but That shouldn't be a problem. I'm not very familiar with generics, but I'm pretty sure that I have a problem with the data not storing primitive data types. How should I fix my code to account for this? The exception comes from the line I have marked near the bottom of my code.
*note: I am testing my code with T is a String. I have not yet tried any other data types. Thanks a lot
public class CircularBuffer<T> {
// properties
private T[] buffer; // the data
private int currentLength; // the current length
private int front; // the index of the logical front of the buffer
private int rear; // the index of the next available place
private int increment;// the increment
private int numFilled = 0;// the number of places filled, defaulted to 0
/**
* Create a new circular buffer with default length (10) and length
* increment(10).
*/
public CircularBuffer() {
T[] buffer = (T[]) new Object[10];
currentLength = 10;
increment = 10;
front = 0;
rear = 0;
} // end of constructor
/**
* Create a new circular buffer with a given length and default length
* increment(10).
*
* @param initialLength
* The initial length of the array.
*/
public CircularBuffer(int initialLength) {
currentLength = initialLength;
T[] buffer = (T[]) new Object[initialLength];
increment = 10;
front = 0;
rear = 0;
} // end of constructor
/**
* Create a new circular buffer with a given length and length increment.
*
* @param initialLength
* The initial length of the array.
* @param initialLength
* The initial length of the array.
*/
public CircularBuffer(int initialLength, int lengthInc) {
currentLength = initialLength;
T[] buffer = (T[]) new Object[initialLength];
increment = lengthInc;
front = 0;
rear = 0;
} // end of constructor
/**
* Add a value to the end of the circular buffer.
*
* @param value
* The value to add.
*
* @throws IllegalArgumentException
* if value is null.
*/
public void add(T value) throws IllegalArgumentException {
if (value == null)
throw new IllegalArgumentException("value is null");
if (numFilled == currentLength) {
T[] temp = (T[]) new Object[currentLength + increment];
for (int n = 0; n < currentLength - 1; n += 1) {
temp[n] = buffer[(front + n) % currentLength];
}
buffer = temp;
front = 0;
rear = currentLength;
currentLength = currentLength + increment;
}
buffer[rear] = value; // getting a null pointer exception here on the buffer[rear] element.
rear = (rear + 1) % currentLength;
numFilled += 1;
} // end of add method
bufferin any of the constructor. You are only assigning a local variable also called buffer in each of the constructors.