This noncompliant example shows a bug in Tomcat version 4.1.24, initially discovered by Reasoning \[[Reasoning 2003|AA. References#Reasoning 03]\]. The {{cardinality}} method was designed to return the number of occurrences of object {{obj}} in collection {{col}}. One valid use of the {{cardinality}} method  is to determine how many objects in the collection are {{null}}. However, because membership in the collection is checked using the expression {{obj.equals(elt)}}, a null pointer dereference is guaranteed whenever {{obj}} is {{null}} and {{elt}} is not {{null}}.

public static int cardinality(Object obj, final Collection col) {
  int count = 0;
  if (col == null) {
    return count;
  }
  Iterator it = col.iterator();
  while (it.hasNext()) {
    Object elt = it.next();
    if ((null == obj && null == elt) || obj.equals(elt)) {  // null pointer dereference
      count++;
    }
  }
  return count;
}

public static int cardinality(Object obj, final Collection col) {
  int count = 0;
  if (col == null) {
    return count;
  }
  Iterator it = col.iterator();
  while (it.hasNext()) {
    Object elt = it.next();
    if ((null == obj && null == elt) ||
        (null != obj && obj.equals(elt))) {
      count++;
    }
  }
  return count;
}

public boolean isName(String s) {
  String names[] = s.split(" ");
  if (names.length != 2) {
    return false;
  }
  return (isCapitalized(names[0]) && isCapitalized(names[1]));
}

public class Foo {
  private boolean isName(String s) {
    String names[] = s.split(" ");
    if (names.length != 2) {
      return false;
    }
    return (isCapitalized(names[0]) && isCapitalized(names[1]));
  }

  public boolean testString(String s) {
    if (s == null) return false;
    else return isName(s);
  }
}

Null pointer dereferences can happen in path-dependent ways. Limitations of automatic detection tools can require manual inspection of code \[[Hovemeyer 2007|AA. References#Hovemeyer 07]\] to detect instances of null pointer dereferences. Annotations for method parameters that must be non-null can reduce the need for manual inspection by assisting automated null pointer dereference detection; use of these annotations is strongly encouraged.

Java Web Start applications and applets particular to JDK version 1.6, prior to update 4, were affected by a bug that had some noteworthy security consequences. In some isolated cases, the application or applet's attempt to establish an HTTPS connection with a server generated a {{NullPointerException}} \[[SDN 2008|AA. References#SDN 08]\]. The resulting failure to establish a secure HTTPS connection with the server caused a denial of service. Clients were temporarily forced to use an insecure HTTP channel for data exchange.