java 出现NullPointerException的原因及解决办法

package java.lang;/** * Thrown when a program tries to access a field or method of an object or an * element of an array when there is no instance or array to use, that is if the * object or array points to {@code null}. It also occurs in some other, less * obvious circumstances, like a {@code throw e} statement where the {@link * Throwable} reference is {@code null}. */public class NullPointerException extends RuntimeException {  private static final long serialVersionUID = 5162710183389028792L;  /**   * Constructs a new {@code NullPointerException} that includes the current   * stack trace.   */  public NullPointerException() {  }  /**   * Constructs a new {@code NullPointerException} with the current stack   * trace and the specified detail message.   *   * @param detailMessage   *      the detail message for this exception.   */  public NullPointerException(String detailMessage) {    super(detailMessage);  }}

void main() {  int* i = NULL;  printf("%#x/n", i);  printf("%#x/n", &i);  system("pause");}