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*
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package java.lang;
Thrown when an application attempts to use null in a case where an object is required. These include:
- Calling the instance method of a
null object. - Accessing or modifying the field of a
null object. - Taking the length of
null as if it were an array. - Accessing or modifying the slots of
null as if it were an array. - Throwing
null as if it were a Throwable value.
Applications should throw instances of this class to indicate other illegal uses of the null object. NullPointerException objects may be constructed by the virtual machine as if suppression were disabled and/or the
stack trace was not writable.
Since: 1.0
/**
* Thrown when an application attempts to use {@code null} in a
* case where an object is required. These include:
* <ul>
* <li>Calling the instance method of a {@code null} object.
* <li>Accessing or modifying the field of a {@code null} object.
* <li>Taking the length of {@code null} as if it were an array.
* <li>Accessing or modifying the slots of {@code null} as if it
* were an array.
* <li>Throwing {@code null} as if it were a {@code Throwable}
* value.
* </ul>
* <p>
* Applications should throw instances of this class to indicate
* other illegal uses of the {@code null} object.
*
* {@code NullPointerException} objects may be constructed by the
* virtual machine as if {@linkplain Throwable#Throwable(String,
* Throwable, boolean, boolean) suppression were disabled and/or the
* stack trace was not writable}.
*
* @since 1.0
*/
public class NullPointerException extends RuntimeException {
@java.io.Serial
private static final long serialVersionUID = 5162710183389028792L;
Constructs a NullPointerException with no detail message. /**
* Constructs a {@code NullPointerException} with no detail message.
*/
public NullPointerException() {
super();
}
Constructs a NullPointerException with the specified detail message. Params: - s – the detail message.
/**
* Constructs a {@code NullPointerException} with the specified
* detail message.
*
* @param s the detail message.
*/
public NullPointerException(String s) {
super(s);
}
// 0: no backtrace filled in, no message computed.
// 1: backtrace filled in, no message computed.
// 2: message computed
private transient int extendedMessageState;
private transient String extendedMessage;
{@inheritDoc}
/**
* {@inheritDoc}
*/
public synchronized Throwable fillInStackTrace() {
// If the stack trace is changed the extended NPE algorithm
// will compute a wrong message. So compute it beforehand.
if (extendedMessageState == 0) {
extendedMessageState = 1;
} else if (extendedMessageState == 1) {
extendedMessage = getExtendedNPEMessage();
extendedMessageState = 2;
}
return super.fillInStackTrace();
}
Returns the detail message string of this throwable.
If a non-null message was supplied in a constructor it is returned. Otherwise, an implementation specific message or null is returned.
Implementation Note:
If no explicit message was passed to the constructor, and as
long as certain internal information is available, a verbose
description of the null reference is returned.
The internal information is not available in deserialized
NullPointerExceptions. Returns: the detail message string, which may be null.
/**
* Returns the detail message string of this throwable.
*
* <p> If a non-null message was supplied in a constructor it is
* returned. Otherwise, an implementation specific message or
* {@code null} is returned.
*
* @implNote
* If no explicit message was passed to the constructor, and as
* long as certain internal information is available, a verbose
* description of the null reference is returned.
* The internal information is not available in deserialized
* NullPointerExceptions.
*
* @return the detail message string, which may be {@code null}.
*/
public String getMessage() {
String message = super.getMessage();
if (message == null) {
synchronized(this) {
if (extendedMessageState == 1) {
// Only the original stack trace was filled in. Message will
// compute correctly.
extendedMessage = getExtendedNPEMessage();
extendedMessageState = 2;
}
return extendedMessage;
}
}
return message;
}
Get an extended exception message. This returns a string describing
the location and cause of the exception. It returns null for
exceptions where this is not applicable.
/**
* Get an extended exception message. This returns a string describing
* the location and cause of the exception. It returns null for
* exceptions where this is not applicable.
*/
private native String getExtendedNPEMessage();
}