This content descriptor contains multiple child content descriptors, and checks each of the against the corresponding other when changes are to be detected.
The content descriptor stores the children in order. This means that the order of the content descriptors are defined during instantiation. When changes are detected, each content descriptor changes will be checked against the argument content descriptor with the same index.
Use the static factory methods to create a new instance.
public | For Externalizable. |
public static ContentDescriptor | create( Creates a new instance for the given content descriptors. |
public static ContentDescriptor | create( Creates a new instance for the given content descriptors. |
public boolean | Indicates whether some other object is "equal to" this one. |
public int | hashCode() Returns a hash code value for the object. |
public boolean | isChanged( Detects changes between this content descriptor and the previous one. |
public void | The object implements the readExternal method to restore its
contents by calling the methods of DataInput for primitive
types and readObject for objects, strings and arrays. |
public String | toString() Returns a string representation of the object. |
public void | The object implements the writeExternal method to save its contents
by calling the methods of DataOutput for its primitive values or
calling the writeObject method of ObjectOutput for objects, strings,
and arrays. |
If the argument is empty, EmptyContentDescriptor will be returned.
If the argument contains only a single descriptor, that single descriptor will be returned.
null
in it.If the argument is empty, EmptyContentDescriptor will be returned.
If the argument contains only a single descriptor, that single descriptor will be returned.
null
in it.
The equals
method implements an equivalence relation on non-null object references:
- It is reflexive: for any non-null reference value
x
,x.equals(x)
should returntrue
. - It is symmetric: for any non-null reference values
x
andy
,x.equals(y)
should returntrue
if and only ify.equals(x)
returnstrue
. - It is transitive: for any non-null reference values
x
,y
, andz
, ifx.equals(y)
returnstrue
andy.equals(z)
returnstrue
, thenx.equals(z)
should returntrue
. - It is consistent: for any non-null reference values
x
andy
, multiple invocations ofx.equals(y)
consistently returntrue
or consistently returnfalse
, provided no information used inequals
comparisons on the objects is modified. - For any non-null reference value
x
,x.equals(null)
should returnfalse
.
The equals
method for class Object
implements the most discriminating possible equivalence
relation on objects; that is, for any non-null reference values x
and y
, this method returns
true
if and only if x
and y
refer to the same object (x == y
has the value
true
).
Note that it is generally necessary to override the hashCode
method whenever this method is overridden,
so as to maintain the general contract for the hashCode
method, which states that equal objects must have
equal hash codes.
true
if this object is the same as the obj argument; false
otherwise.
The general contract of hashCode
is:
- Whenever it is invoked on the same object more than once during an execution of a Java application, the
hashCode
method must consistently return the same integer, provided no information used inequals
comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application. - If two objects are equal according to the
equals(Object)
method, then calling thehashCode
method on each of the two objects must produce the same integer result. - It is not required that if two objects are unequal according to the
Object.equals(
Object) method, then calling thehashCode
method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.
As much as is reasonably practical, the hashCode method defined by class Object
does return distinct
integers for distinct objects. (This is typically implemented by converting the internal address of the object
into an integer, but this implementation technique is not required by the Java™ programming language.)
The default implementation compares the two objects using ContentDescriptor.equals(
Implementations are encouraged to check the type of the parameter using instanceof
before casting
them. It is further encouraged to check the content differences against interfaces instead of direct class
implementations.
One can think about this function as this
is the expected content of a file, and the parameter is
the actual contents. If this method returns true
then the file associated with this
should replace the file associated with the parameter contents. This is mainly used when synchronizing files in
memory to the filesystem.
null
to represent that the previous content
doesn't exist.true
if the contents described by this descriptor differs from the parameter.toString
method returns a string that
"textually represents" this object. The result should be a concise but informative representation that is easy
for a person to read. It is recommended that all subclasses override this method.
The toString
method for class Object
returns a string consisting of the name of the class of
which the object is an instance, the at-sign character `@
', and the unsigned hexadecimal representation
of the hash code of the object. In other words, this method returns a string equal to the value of:
getClass().getName() + '@' + Integer.toHexString(hashCode())