为什么我的环形缓冲区/循环缓冲区在java中被破坏了

Question

我的addFront方法我相信是一切崩溃的原因。isEmpty（）方法已经构建，但我不确定这是否是它崩溃的原因。

public class ExpandableArrayBuffer implements ExpandableBuffer {
     private static final int DEFAULT_CAPACITY = 10;
    String[] elements; 
    int size = 0;
    int rear = 0;
    int front = 0; 
    //constructor
      public ExpandableArrayBuffer(int size) {
            this.size = size;   
        // Make it that size
    }
      public ExpandableArrayBuffer(){
       this(DEFAULT_CAPACITY);
      }
    @Override
    public boolean isEmpty() {
        return front == rear; 
        }
    @Override
    public void addFront(String s) {
        if(front<0||front>elements.length){
           int temp=0;
           front=temp;
       }
        if(isEmpty()){
           elements[0]=s;
        }else{
       s=elements[front];
       }
       front--;
       size++;
       }

    @Override
    public void addRear(String s) {
     int avail = (front + size) % elements.length;
        elements[avail] = s;
        size++;
    }
    @Override
    public String removeFront() {
     String answer = elements[front];
     elements[front] = null; 
     front = (front + 1) % elements.length;
     size--;
     return answer;
    }
    @Override
    public String removeRear() {
        String keysersoze = elements [rear];
        elements[rear] = null;
        rear = (rear + size) % elements.length;
        size--;
        return keysersoze;
    }
    public int size(){
        return size;
    }
}

---

public interface ExpandableBuffer {
    /**
     * Returns true if this buffer contains no elements.
     * @return true if this buffer contains no elements
     */
    boolean isEmpty();
    /**
     * Adds the specified string to the front of this buffer.
     * @param s string to be added to this buffer
     */
    void addFront(String s);
    /**
     * Adds the specified string to the rear of this buffer.
     * @param s string to be added to this buffer
     */
    void addRear(String s);
    /**
     * Removes and returns the string at the front of this buffer.
     * @return the string at the front of this buffer
     */
    String removeFront();
    /**
     * Removes and returns the string at the rear of this buffer.
     * @return the string at the rear of this buffer
     */
    String removeRear();
    /**
     * Returns a string representation of this buffer. The string representation
     * consists of a list of this buffer's Strings in order from front to rear,
     * enclosed in square brackets ("[]"). Adjacent Strings are
     * separated by the characters ", " (comma and space). The letter
     * "R" should appear to the left to indicate the rear of the buffer and the
     * letter "F" should appear to the right to indicate the front of the
     * buffer. Fore example, a buffer containing the strings "A", "B", and "C"
     * would be represented as "R[A, B, C]F".
     *
     * @return a string representation of this buffer
     */    
    String toString();
}

---

这是一个运行和测试其他类的主类

  public class CBufferApp {
    static String message;
    static ExpandableBuffer buffer;
    public static void main(String[] args) {
        buffer = new ExpandableArrayBuffer();
        message = " 1) Initial buffer";
        print();
        buffer.addFront("A");
        message = " 2) Add A to front";
        print();
        buffer.addFront("B");
        message = " 3) Add B to front";
        print();
        buffer.addFront("C");
        message = " 4) Add C to front";
        print();
        buffer.removeRear();
        message = " 5) Remove rear";
        print();
        buffer.removeRear();
        message = " 6) Remove rear";
        print();
        buffer.removeRear();
        message = " 7) Remove rear";
        print();
        buffer.addFront("D");
        message = " 8) Add D to front";
        print();
        buffer.addFront("E");
        message = " 9) Add E to front";
        print();
        buffer.removeRear();
        message = "10) Remove rear";
        print();
        buffer.removeRear();
        message = "11) Remove rear";
        print();
        buffer.addRear("F");
        message = "12) Add F to rear";
        print();
        buffer.addRear("G");
        message = "13) Add G to rear";
        print();
        buffer.addFront("H");
        message = "14) Add H to front";
        print();
        buffer.addFront("I");
        message = "15) Add I to front";
        print();
        buffer.addFront("J");
        message = "16) Add J to front";
        print();
        buffer.addFront("K");
        message = "17) Add K to front";
        print();
        buffer.addRear("L");
        message = "18) Add L to rear";
        print();
        buffer.addRear("M");
        message = "19) Add M to rear";
        print();
        buffer.addRear("N");
        message = "20) Add N to rear";
        print();
        buffer.addRear("O");
        message = "21) Add O to rear";
        print();
        buffer.addRear("P");
        message = "22) Add P to rear";
        print();
    }
    private static void print(){
        String emptyMessage = "";
        if(buffer.isEmpty()){
            emptyMessage = "Empty";
        }
        System.out.printf("%-23s %-7s", message, emptyMessage);
        System.out.println(buffer);
    }
}

Answer 1

正如其他人所说：使用调试器，但在这种情况下，看看代码，很明显哪里出了问题，要理解这一点：

1. 数组被视为对象，因此将元素定义为String[]类型的变量使其成为可以引用String数组的变量
2. 当引用变量被定义为类的属性（如元素）时，它们将使用null指针进行初始化
3. 对元素的所有引用。元素的长度是指元素引用的数组的长度
4. 由于在代码中没有任何地方真正创建像newString[5]这样的字符串数组并将其分配给元素，因此所有对elements.length的引用都将导致NullPointerException