Question

我正在进行一项任务，我不得不在数组中存储未知类型的数据，并与该数组进行交互。我正在测试我的代码，当我尝试将第一个值添加到数组时，我得到一个空指针异常。该值应为null，但这不应该是一个问题。我对泛型不是很熟悉，但我很确定我的数据没有存储原始数据类型有问题。我应该如何修复我的代码来解决这个问题？例外来自我在代码底部附近标记的行。

*注意：我正在测试我的代码，T是一个字符串。我还没有尝试过任何其他数据类型。非常感谢

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

Answer 1

代码

T[] buffer = (T[]) new Object[initialLength];

构造函数中的

创建局部变量 buffer并将其设置为数组。字段 this.buffer保持为空，永不分配。相反，使用

buffer = (T[]) new Object[initialLength];

更改一个空的泛型数组时出现意外的空指针异常

1 个答案: