Wednesday, November 25, 2015

Document methods

 

Interface Document

  • All Superinterfaces:
    Node
    All Known Implementing Classes:
    SOAPPart

    public interface Document
extends Node
    The Document interface represents the entire HTML or XML document. Conceptually, it is the root of the document tree, and provides the primary access to the document's data. Since elements, text nodes, comments, processing instructions, etc. cannot exist outside the context of a Document, the Document interface also contains the factory methods needed to create these objects. The Node objects created have a ownerDocument attribute which associates them with the Document within whose context they were created. See also the Document Object Model (DOM) Level 3 Core Specification.

    • Method Detail

      • getDoctype

        DocumentType getDoctype()
        The Document Type Declaration (see DocumentType) associated with this document. For XML documents without a document type declaration this returns null. For HTML documents, a DocumentType object may be returned, independently of the presence or absence of document type declaration in the HTML document.
        This provides direct access to the DocumentType node, child node of this Document. This node can be set at document creation time and later changed through the use of child nodes manipulation methods, such as Node.insertBefore, or Node.replaceChild. Note, however, that while some implementations may instantiate different types of Document objects supporting additional features than the "Core", such as "HTML" [DOM Level 2 HTML] , based on the DocumentType specified at creation time, changing it afterwards is very unlikely to result in a change of the features supported.
        Since:
        DOM Level 3

      • getImplementation

        DOMImplementation getImplementation()
        The DOMImplementation object that handles this document. A DOM application may use objects from multiple implementations.

      • getDocumentElement

        Element getDocumentElement()
        This is a convenience attribute that allows direct access to the child node that is the document element of the document.

      • createElement

        Element createElement(String tagName)
               throws DOMException
        Creates an element of the type specified. Note that the instance returned implements the Element interface, so attributes can be specified directly on the returned object.
        In addition, if there are known attributes with default values, Attr nodes representing them are automatically created and attached to the element.
        To create an element with a qualified name and namespace URI, use the createElementNS method.
        Parameters:
        tagName - The name of the element type to instantiate. For XML, this is case-sensitive, otherwise it depends on the case-sensitivity of the markup language in use. In that case, the name is mapped to the canonical form of that markup by the DOM implementation.
        Returns:
        A new Element object with the nodeName attribute set to tagName, and localName, prefix, and namespaceURI set to null.
        Throws:
        DOMException - INVALID_CHARACTER_ERR: Raised if the specified name is not an XML name according to the XML version in use specified in the Document.xmlVersion attribute.

      • createDocumentFragment

        DocumentFragment createDocumentFragment()
        Creates an empty DocumentFragment object.
        Returns:
        A new DocumentFragment.

      • createTextNode

        Text createTextNode(String data)
        Creates a Text node given the specified string.
        Parameters:
        data - The data for the node.
        Returns:
        The new Text object.

      • createComment

        Comment createComment(String data)
        Creates a Comment node given the specified string.
        Parameters:
        data - The data for the node.
        Returns:
        The new Comment object.

      • createCDATASection

        CDATASection createCDATASection(String data)
                         throws DOMException
        Creates a CDATASection node whose value is the specified string.
        Parameters:
        data - The data for the CDATASection contents.
        Returns:
        The new CDATASection object.
        Throws:
        DOMException - NOT_SUPPORTED_ERR: Raised if this document is an HTML document.

      • createProcessingInstruction

        ProcessingInstruction createProcessingInstruction(String target,
                                                  String data)
                                           throws DOMException
        Creates a ProcessingInstruction node given the specified name and data strings.
        Parameters:
        target - The target part of the processing instruction.Unlike Document.createElementNS or Document.createAttributeNS, no namespace well-formed checking is done on the target name. Applications should invoke Document.normalizeDocument() with the parameter " namespaces" set to true in order to ensure that the target name is namespace well-formed.
        data - The data for the node.
        Returns:
        The new ProcessingInstruction object.
        Throws:
        DOMException - INVALID_CHARACTER_ERR: Raised if the specified target is not an XML name according to the XML version in use specified in the Document.xmlVersion attribute.
        NOT_SUPPORTED_ERR: Raised if this document is an HTML document.

      • createAttribute

        Attr createAttribute(String name)
              throws DOMException
        Creates an Attr of the given name. Note that the Attr instance can then be set on an Element using the setAttributeNode method.
        To create an attribute with a qualified name and namespace URI, use the createAttributeNS method.
        Parameters:
        name - The name of the attribute.
        Returns:
        A new Attr object with the nodeName attribute set to name, and localName, prefix, and namespaceURI set to null. The value of the attribute is the empty string.
        Throws:
        DOMException - INVALID_CHARACTER_ERR: Raised if the specified name is not an XML name according to the XML version in use specified in the Document.xmlVersion attribute.

      • createEntityReference

        EntityReference createEntityReference(String name)
                               throws DOMException
        Creates an EntityReference object. In addition, if the referenced entity is known, the child list of the EntityReference node is made the same as that of the corresponding Entity node. Note: If any descendant of the Entity node has an unbound namespace prefix, the corresponding descendant of the created EntityReference node is also unbound; (its namespaceURI is null). The DOM Level 2 and 3 do not support any mechanism to resolve namespace prefixes in this case.
        Parameters:
        name - The name of the entity to reference.Unlike Document.createElementNS or Document.createAttributeNS, no namespace well-formed checking is done on the entity name. Applications should invoke Document.normalizeDocument() with the parameter " namespaces" set to true in order to ensure that the entity name is namespace well-formed.
        Returns:
        The new EntityReference object.
        Throws:
        DOMException - INVALID_CHARACTER_ERR: Raised if the specified name is not an XML name according to the XML version in use specified in the Document.xmlVersion attribute.
        NOT_SUPPORTED_ERR: Raised if this document is an HTML document.

      • getElementsByTagName

        NodeList getElementsByTagName(String tagname)
        Returns a NodeList of all the Elements in document order with a given tag name and are contained in the document.
        Parameters:
        tagname - The name of the tag to match on. The special value "*" matches all tags. For XML, the tagname parameter is case-sensitive, otherwise it depends on the case-sensitivity of the markup language in use.
        Returns:
        A new NodeList object containing all the matched Elements.

      • importNode

        Node importNode(Node importedNode,
                boolean deep)
         throws DOMException
        Imports a node from another document to this document, without altering or removing the source node from the original document; this method creates a new copy of the source node. The returned node has no parent; (parentNode is null).
        For all nodes, importing a node creates a node object owned by the importing document, with attribute values identical to the source node's nodeName and nodeType, plus the attributes related to namespaces (prefix, localName, and namespaceURI). As in the cloneNode operation, the source node is not altered. User data associated to the imported node is not carried over. However, if any UserDataHandlers has been specified along with the associated data these handlers will be called with the appropriate parameters before this method returns.
        Additional information is copied as appropriate to the nodeType, attempting to mirror the behavior expected if a fragment of XML or HTML source was copied from one document to another, recognizing that the two documents may have different DTDs in the XML case. The following list describes the specifics for each type of node.
        ATTRIBUTE_NODE
        The ownerElement attribute is set to null and the specified flag is set to true on the generated Attr. The descendants of the source Attr are recursively imported and the resulting nodes reassembled to form the corresponding subtree. Note that the deep parameter has no effect on Attr nodes; they always carry their children with them when imported.
        DOCUMENT_FRAGMENT_NODE
        If the deep option was set to true, the descendants of the source DocumentFragment are recursively imported and the resulting nodes reassembled under the imported DocumentFragment to form the corresponding subtree. Otherwise, this simply generates an empty DocumentFragment.
        DOCUMENT_NODE
        Document nodes cannot be imported.
        DOCUMENT_TYPE_NODE
        DocumentType nodes cannot be imported.
        ELEMENT_NODE
        Specified attribute nodes of the source element are imported, and the generated Attr nodes are attached to the generated Element. Default attributes are not copied, though if the document being imported into defines default attributes for this element name, those are assigned. If the importNode deep parameter was set to true, the descendants of the source element are recursively imported and the resulting nodes reassembled to form the corresponding subtree.
        ENTITY_NODE
        Entity nodes can be imported, however in the current release of the DOM the DocumentType is readonly. Ability to add these imported nodes to a DocumentType will be considered for addition to a future release of the DOM.On import, the publicId, systemId, and notationName attributes are copied. If a deep import is requested, the descendants of the the source Entity are recursively imported and the resulting nodes reassembled to form the corresponding subtree.
        ENTITY_REFERENCE_NODE
        Only the EntityReference itself is copied, even if a deep import is requested, since the source and destination documents might have defined the entity differently. If the document being imported into provides a definition for this entity name, its value is assigned.
        NOTATION_NODE
        Notation nodes can be imported, however in the current release of the DOM the DocumentType is readonly. Ability to add these imported nodes to a DocumentType will be considered for addition to a future release of the DOM.On import, the publicId and systemId attributes are copied. Note that the deep parameter has no effect on this type of nodes since they cannot have any children.
        PROCESSING_INSTRUCTION_NODE
        The imported node copies its target and data values from those of the source node.Note that the deep parameter has no effect on this type of nodes since they cannot have any children.
        TEXT_NODE, CDATA_SECTION_NODE, COMMENT_NODE
        These three types of nodes inheriting from CharacterData copy their data and length attributes from those of the source node.Note that the deep parameter has no effect on these types of nodes since they cannot have any children.
        Parameters:
        importedNode - The node to import.
        deep - If true, recursively import the subtree under the specified node; if false, import only the node itself, as explained above. This has no effect on nodes that cannot have any children, and on Attr, and EntityReference nodes.
        Returns:
        The imported node that belongs to this Document.
        Throws:
        DOMException - NOT_SUPPORTED_ERR: Raised if the type of node being imported is not supported.
        INVALID_CHARACTER_ERR: Raised if one of the imported names is not an XML name according to the XML version in use specified in the Document.xmlVersion attribute. This may happen when importing an XML 1.1 [XML 1.1] element into an XML 1.0 document, for instance.
        Since:
        DOM Level 2

      • createElementNS

        Element createElementNS(String namespaceURI,
                        String qualifiedName)
                 throws DOMException
        Creates an element of the given qualified name and namespace URI.
        Per [XML Namespaces] , applications must use the value null as the namespaceURI parameter for methods if they wish to have no namespace.
        Parameters:
        namespaceURI - The namespace URI of the element to create.
        qualifiedName - The qualified name of the element type to instantiate.
        Returns:
        A new Element object with the following attributes:
        AttributeValue
        Node.nodeNamequalifiedName
        Node.namespaceURInamespaceURI
        Node.prefixprefix, extracted from qualifiedName, or null if there is no prefix
        Node.localNamelocal name, extracted from qualifiedName
        Element.tagNamequalifiedName
        Throws:
        DOMException - INVALID_CHARACTER_ERR: Raised if the specified qualifiedName is not an XML name according to the XML version in use specified in the Document.xmlVersion attribute.
        NAMESPACE_ERR: Raised if the qualifiedName is a malformed qualified name, if the qualifiedName has a prefix and the namespaceURI is null, or if the qualifiedName has a prefix that is "xml" and the namespaceURI is different from " http://www.w3.org/XML/1998/namespace" [XML Namespaces] , or if the qualifiedName or its prefix is "xmlns" and the namespaceURI is different from "http://www.w3.org/2000/xmlns/", or if the namespaceURI is "http://www.w3.org/2000/xmlns/" and neither the qualifiedName nor its prefix is "xmlns".
        NOT_SUPPORTED_ERR: Always thrown if the current document does not support the "XML" feature, since namespaces were defined by XML.
        Since:
        DOM Level 2

      • createAttributeNS

        Attr createAttributeNS(String namespaceURI,
                       String qualifiedName)
                throws DOMException
        Creates an attribute of the given qualified name and namespace URI.
        Per [XML Namespaces] , applications must use the value null as the namespaceURI parameter for methods if they wish to have no namespace.
        Parameters:
        namespaceURI - The namespace URI of the attribute to create.
        qualifiedName - The qualified name of the attribute to instantiate.
        Returns:
        A new Attr object with the following attributes:
        AttributeValue
        Node.nodeNamequalifiedName
        Node.namespaceURInamespaceURI
        Node.prefixprefix, extracted from qualifiedName, or null if there is no prefix
        Node.localNamelocal name, extracted from qualifiedName
        Attr.namequalifiedName
        Node.nodeValuethe empty string
        Throws:
        DOMException - INVALID_CHARACTER_ERR: Raised if the specified qualifiedName is not an XML name according to the XML version in use specified in the Document.xmlVersion attribute.
        NAMESPACE_ERR: Raised if the qualifiedName is a malformed qualified name, if the qualifiedName has a prefix and the namespaceURI is null, if the qualifiedName has a prefix that is "xml" and the namespaceURI is different from " http://www.w3.org/XML/1998/namespace", if the qualifiedName or its prefix is "xmlns" and the namespaceURI is different from "http://www.w3.org/2000/xmlns/", or if the namespaceURI is "http://www.w3.org/2000/xmlns/" and neither the qualifiedName nor its prefix is "xmlns".
        NOT_SUPPORTED_ERR: Always thrown if the current document does not support the "XML" feature, since namespaces were defined by XML.
        Since:
        DOM Level 2

      • getElementsByTagNameNS

        NodeList getElementsByTagNameNS(String namespaceURI,
                                String localName)
        Returns a NodeList of all the Elements with a given local name and namespace URI in document order.
        Parameters:
        namespaceURI - The namespace URI of the elements to match on. The special value "*" matches all namespaces.
        localName - The local name of the elements to match on. The special value "*" matches all local names.
        Returns:
        A new NodeList object containing all the matched Elements.
        Since:
        DOM Level 2

      • getElementById

        Element getElementById(String elementId)
        Returns the Element that has an ID attribute with the given value. If no such element exists, this returns null . If more than one element has an ID attribute with that value, what is returned is undefined.
        The DOM implementation is expected to use the attribute Attr.isId to determine if an attribute is of type ID. Note: Attributes with the name "ID" or "id" are not of type ID unless so defined.
        Parameters:
        elementId - The unique id value for an element.
        Returns:
        The matching element or null if there is none.
        Since:
        DOM Level 2

      • getInputEncoding

        String getInputEncoding()
        An attribute specifying the encoding used for this document at the time of the parsing. This is null when it is not known, such as when the Document was created in memory.
        Since:
        DOM Level 3

      • getXmlEncoding

        String getXmlEncoding()
        An attribute specifying, as part of the XML declaration, the encoding of this document. This is null when unspecified or when it is not known, such as when the Document was created in memory.
        Since:
        DOM Level 3

      • getXmlStandalone

        boolean getXmlStandalone()
        An attribute specifying, as part of the XML declaration, whether this document is standalone. This is false when unspecified. Note: No verification is done on the value when setting this attribute. Applications should use Document.normalizeDocument() with the "validate" parameter to verify if the value matches the validity constraint for standalone document declaration as defined in [XML 1.0].
        Since:
        DOM Level 3

      • setXmlStandalone

        void setXmlStandalone(boolean xmlStandalone)
               throws DOMException
        An attribute specifying, as part of the XML declaration, whether this document is standalone. This is false when unspecified. Note: No verification is done on the value when setting this attribute. Applications should use Document.normalizeDocument() with the "validate" parameter to verify if the value matches the validity constraint for standalone document declaration as defined in [XML 1.0].
        Throws:
        DOMException - NOT_SUPPORTED_ERR: Raised if this document does not support the "XML" feature.
        Since:
        DOM Level 3

      • getXmlVersion

        String getXmlVersion()
        An attribute specifying, as part of the XML declaration, the version number of this document. If there is no declaration and if this document supports the "XML" feature, the value is "1.0". If this document does not support the "XML" feature, the value is always null. Changing this attribute will affect methods that check for invalid characters in XML names. Application should invoke Document.normalizeDocument() in order to check for invalid characters in the Nodes that are already part of this Document.
        DOM applications may use the DOMImplementation.hasFeature(feature, version) method with parameter values "XMLVersion" and "1.0" (respectively) to determine if an implementation supports [XML 1.0]. DOM applications may use the same method with parameter values "XMLVersion" and "1.1" (respectively) to determine if an implementation supports [XML 1.1]. In both cases, in order to support XML, an implementation must also support the "XML" feature defined in this specification. Document objects supporting a version of the "XMLVersion" feature must not raise a NOT_SUPPORTED_ERR exception for the same version number when using Document.xmlVersion.
        Since:
        DOM Level 3

      • setXmlVersion

        void setXmlVersion(String xmlVersion)
            throws DOMException
        An attribute specifying, as part of the XML declaration, the version number of this document. If there is no declaration and if this document supports the "XML" feature, the value is "1.0". If this document does not support the "XML" feature, the value is always null. Changing this attribute will affect methods that check for invalid characters in XML names. Application should invoke Document.normalizeDocument() in order to check for invalid characters in the Nodes that are already part of this Document.
        DOM applications may use the DOMImplementation.hasFeature(feature, version) method with parameter values "XMLVersion" and "1.0" (respectively) to determine if an implementation supports [XML 1.0]. DOM applications may use the same method with parameter values "XMLVersion" and "1.1" (respectively) to determine if an implementation supports [XML 1.1]. In both cases, in order to support XML, an implementation must also support the "XML" feature defined in this specification. Document objects supporting a version of the "XMLVersion" feature must not raise a NOT_SUPPORTED_ERR exception for the same version number when using Document.xmlVersion.
        Throws:
        DOMException - NOT_SUPPORTED_ERR: Raised if the version is set to a value that is not supported by this Document or if this document does not support the "XML" feature.
        Since:
        DOM Level 3

      • getStrictErrorChecking

        boolean getStrictErrorChecking()
        An attribute specifying whether error checking is enforced or not. When set to false, the implementation is free to not test every possible error case normally defined on DOM operations, and not raise any DOMException on DOM operations or report errors while using Document.normalizeDocument(). In case of error, the behavior is undefined. This attribute is true by default.
        Since:
        DOM Level 3

      • setStrictErrorChecking

        void setStrictErrorChecking(boolean strictErrorChecking)
        An attribute specifying whether error checking is enforced or not. When set to false, the implementation is free to not test every possible error case normally defined on DOM operations, and not raise any DOMException on DOM operations or report errors while using Document.normalizeDocument(). In case of error, the behavior is undefined. This attribute is true by default.
        Since:
        DOM Level 3

      • getDocumentURI

        String getDocumentURI()
        The location of the document or null if undefined or if the Document was created using DOMImplementation.createDocument. No lexical checking is performed when setting this attribute; this could result in a null value returned when using Node.baseURI .
        Beware that when the Document supports the feature "HTML" [DOM Level 2 HTML] , the href attribute of the HTML BASE element takes precedence over this attribute when computing Node.baseURI.
        Since:
        DOM Level 3

      • setDocumentURI

        void setDocumentURI(String documentURI)
        The location of the document or null if undefined or if the Document was created using DOMImplementation.createDocument. No lexical checking is performed when setting this attribute; this could result in a null value returned when using Node.baseURI .
        Beware that when the Document supports the feature "HTML" [DOM Level 2 HTML] , the href attribute of the HTML BASE element takes precedence over this attribute when computing Node.baseURI.
        Since:
        DOM Level 3

      • adoptNode

        Node adoptNode(Node source)
        throws DOMException
        Attempts to adopt a node from another document to this document. If supported, it changes the ownerDocument of the source node, its children, as well as the attached attribute nodes if there are any. If the source node has a parent it is first removed from the child list of its parent. This effectively allows moving a subtree from one document to another (unlike importNode() which create a copy of the source node instead of moving it). When it fails, applications should use Document.importNode() instead. Note that if the adopted node is already part of this document (i.e. the source and target document are the same), this method still has the effect of removing the source node from the child list of its parent, if any. The following list describes the specifics for each type of node.
        ATTRIBUTE_NODE
        The ownerElement attribute is set to null and the specified flag is set to true on the adopted Attr. The descendants of the source Attr are recursively adopted.
        DOCUMENT_FRAGMENT_NODE
        The descendants of the source node are recursively adopted.
        DOCUMENT_NODE
        Document nodes cannot be adopted.
        DOCUMENT_TYPE_NODE
        DocumentType nodes cannot be adopted.
        ELEMENT_NODE
        Specified attribute nodes of the source element are adopted. Default attributes are discarded, though if the document being adopted into defines default attributes for this element name, those are assigned. The descendants of the source element are recursively adopted.
        ENTITY_NODE
        Entity nodes cannot be adopted.
        ENTITY_REFERENCE_NODE
        Only the EntityReference node itself is adopted, the descendants are discarded, since the source and destination documents might have defined the entity differently. If the document being imported into provides a definition for this entity name, its value is assigned.
        NOTATION_NODE
        Notation nodes cannot be adopted.
        PROCESSING_INSTRUCTION_NODE, TEXT_NODE, CDATA_SECTION_NODE, COMMENT_NODE
        These nodes can all be adopted. No specifics.
        Note: Since it does not create new nodes unlike the Document.importNode() method, this method does not raise an INVALID_CHARACTER_ERR exception, and applications should use the Document.normalizeDocument() method to check if an imported name is not an XML name according to the XML version in use.
        Parameters:
        source - The node to move into this document.
        Returns:
        The adopted node, or null if this operation fails, such as when the source node comes from a different implementation.
        Throws:
        DOMException - NOT_SUPPORTED_ERR: Raised if the source node is of type DOCUMENT, DOCUMENT_TYPE.
        NO_MODIFICATION_ALLOWED_ERR: Raised when the source node is readonly.
        Since:
        DOM Level 3

      • getDomConfig

        DOMConfiguration getDomConfig()
        The configuration used when Document.normalizeDocument() is invoked.
        Since:
        DOM Level 3

      • normalizeDocument

        void normalizeDocument()
        This method acts as if the document was going through a save and load cycle, putting the document in a "normal" form. As a consequence, this method updates the replacement tree of EntityReference nodes and normalizes Text nodes, as defined in the method Node.normalize().
        Otherwise, the actual result depends on the features being set on the Document.domConfig object and governing what operations actually take place. Noticeably this method could also make the document namespace well-formed according to the algorithm described in , check the character normalization, remove the CDATASection nodes, etc. See DOMConfiguration for details. 
        // Keep in the document
 the information defined // in the XML Information Set (Java example)
 DOMConfiguration docConfig = myDocument.getDomConfig();
 docConfig.setParameter("infoset", Boolean.TRUE);
 myDocument.normalizeDocument();

        Mutation events, when supported, are generated to reflect the changes occurring on the document.
        If errors occur during the invocation of this method, such as an attempt to update a read-only node or a Node.nodeName contains an invalid character according to the XML version in use, errors or warnings (DOMError.SEVERITY_ERROR or DOMError.SEVERITY_WARNING) will be reported using the DOMErrorHandler object associated with the "error-handler " parameter. Note this method might also report fatal errors ( DOMError.SEVERITY_FATAL_ERROR) if an implementation cannot recover from an error.
        Since:
        DOM Level 3

      • renameNode

        Node renameNode(Node n,
                String namespaceURI,
                String qualifiedName)
         throws DOMException
        Rename an existing node of type ELEMENT_NODE or ATTRIBUTE_NODE.
        When possible this simply changes the name of the given node, otherwise this creates a new node with the specified name and replaces the existing node with the new node as described below.
        If simply changing the name of the given node is not possible, the following operations are performed: a new node is created, any registered event listener is registered on the new node, any user data attached to the old node is removed from that node, the old node is removed from its parent if it has one, the children are moved to the new node, if the renamed node is an Element its attributes are moved to the new node, the new node is inserted at the position the old node used to have in its parent's child nodes list if it has one, the user data that was attached to the old node is attached to the new node.
        When the node being renamed is an Element only the specified attributes are moved, default attributes originated from the DTD are updated according to the new element name. In addition, the implementation may update default attributes from other schemas. Applications should use Document.normalizeDocument() to guarantee these attributes are up-to-date.
        When the node being renamed is an Attr that is attached to an Element, the node is first removed from the Element attributes map. Then, once renamed, either by modifying the existing node or creating a new one as described above, it is put back.
        In addition,
        • a user data event NODE_RENAMED is fired,
        • when the implementation supports the feature "MutationNameEvents", each mutation operation involved in this method fires the appropriate event, and in the end the event { http://www.w3.org/2001/xml-events, DOMElementNameChanged} or { http://www.w3.org/2001/xml-events, DOMAttributeNameChanged} is fired.
        • Parameters:
        n - The node to rename.
        namespaceURI - The new namespace URI.
        qualifiedName - The new qualified name.
        Returns:
        The renamed node. This is either the specified node or the new node that was created to replace the specified node.
        Throws:
        DOMException - NOT_SUPPORTED_ERR: Raised when the type of the specified node is neither ELEMENT_NODE nor ATTRIBUTE_NODE, or if the implementation does not support the renaming of the document element.
        INVALID_CHARACTER_ERR: Raised if the new qualified name is not an XML name according to the XML version in use specified in the Document.xmlVersion attribute.
        WRONG_DOCUMENT_ERR: Raised when the specified node was created from a different document than this document.
        NAMESPACE_ERR: Raised if the qualifiedName is a malformed qualified name, if the qualifiedName has a prefix and the namespaceURI is null, or if the qualifiedName has a prefix that is "xml" and the namespaceURI is different from " http://www.w3.org/XML/1998/namespace" [XML Namespaces] . Also raised, when the node being renamed is an attribute, if the qualifiedName, or its prefix, is "xmlns" and the namespaceURI is different from "http://www.w3.org/2000/xmlns/".
        Since:
         
Posted by at No comments:

Tuesday, November 10, 2015

Overriding Rules

Difference between Method Overloading and Overriding in Java?

Method Overloading vs Method Overriding
Though name of method remains same in case of both method overloading and overriding, main difference comes form the fact that method overloading is resolved during compile time, while method overriding is resolved at runtime. Also rules of overriding or overloading a method is different in Java. For example, private, static and final method cannot be overriding in Java but you can still overload them. For overriding both name and signature of method must remain same, but in for overloading method signature must be different. Last but not the least difference between them is that call to overloaded methods are resolved using static binding while call to overridden method is resolved using dynamic binding in Java.  By the way, Method overloading and method overriding in Java is two important concept in Java which allows Java programmer to declare method with same name but different behavior. Method overloading and method overriding is based on Polymorphism in Java. In case of method overloading, method with same name co-exists in same class but they must have different method signature, while in case of method overriding, method with same name is declared in derived class or sub class.Method overloading is resolved using static binding in Java at compile time while method overriding is resolved using dynamic binding in Java at runtime. In short When you overload a method in Java its method signature got changed while in case of overriding method signature remains same but a method can only be overridden in sub class. Since Java supports Polymorphism and resolve object at run-time it is capable to call overridden method in Java. By the way difference between method overloading and overriding is also one of the popular Java design question and appear in almost all levels of Java interviews.



What is method overloading and overriding in Java?

In this Java tutorial we will see how Java allows you to create two methods of same name by using method overloading and method overriding. We will also touch base on how methods are bonded or called by Compiler and Java Virtual Machine and finally we will answer of popular interview questions difference between method overloading and method overriding in Java. This article is in my series of Java article which discusses about Interview e.g. Difference between Synchronized Collection and Concurrent Collection or How to Stop Thread in Java. Please let me know if you have some other interview questions and you are looking answer or reason for that and here in Javarevisited we will try to find and discuss those interview questions.



How to Overload a Method in Java

If you have two methods with same name in one Java class with different method signature than its called overloaded method in Java. Generally overloaded method in Java has different set of arguments to perform something based on different number of input. You can also overload constructor in Java, which we will see in following example of method overloading in Java. Binding of overloading method occurs during compile time and overloaded calls resolved using static binding. To overload a Java method just changes its signature. Just remember in order to change signature you either need to change number of argument, type of argument or order of argument in Java if they are of different types. Since return type is not part of method signature simply changing return type will result in duplicate method and you will get compile time error in Java. In our example of Loan and PersonalLoan class, createLoan method is overloaded. Since you have two crateLoan() method with one takes one argument lender while other take two argument both lender and interestRate. Remember you can overload static method in Java, you can also overload private and final method in Java but you can not override them.



How to Override a Method in Java

In order to override a Java method, you need to create a child class which extends parent. Overridden method in Java also shares same name as original method in Java but can only be overridden in sub class. Original method has to be defined inside interface or base class, which can be abstract as well. When youoverride a method in Java its signature remains exactly same including return type. JVM resolves correct overridden method based upon object at run-time by using dynamic binding in Java. For example in our case when we call personalLoan.toString() method even though personalLoan object is of type Loan actual method called would be from PersonalLoan class because object referenced by personalLoan variable is of type PersonalLoan(). This is very useful technique to modify behavior of a function in Java based on different implementation. equals(), hashcode() and compareTo() methods are classic example of overridden methods in Java.

Another important point is that you can not override static method in Java because they are associated with Class rather than object and resolved and bonded during compile time and that’s the reason you cannot override main method in Java. Similar to static, private and final methods are also not overridden in Java. By the way, as part of overriding best practice, always use @Override annotation, while overriding method from an abstract class or interface.


Rules of Method Overriding in Java

Following are rules of method overriding in java which must be followed while overriding any method. As stated earlier private, static and final method can not be overridden in Java. 
  1. Method signature must be same including return type, number of method parameters, type of parameters and order of parameters 
  2. Overriding method can not throw higher Exception than original or overridden method. means if original method throws IOException than overriding method can not throw super class of IOException e.g. Exception but it can throw any sub class of IOException or simply does not throw any Exception. This rule only applies to checked Exception in Java, overridden method is free to throw any unchecked Exception. 
  3. Overriding method can not reduce accessibility of overridden method , means if original or overridden method is public than overriding method can not make it protected. 


Difference between Method Overloading vs Overriding in Java

Overloading vs Overriding in Java is one of the popular java interview questions at many companies and asked at different levels of programmers. Here are some important difference between overloading and overriding in Java. Though It's more important is to understand how to use both overloading and overriding, these difference are good from interview perspective and gives some basic idea as well:

1) First and most important difference between method overloading and overriding is that, In case of method overloading in Java, signature of method changes while in case of method overriding it remain same.

2) Second major difference between method overloading vs overriding in Java is that You can overload method in one class but overriding can only be done on subclass.

3) You can not override static, final and private method in Java but you can overload static, final or private method in Java.

4) Overloaded method in Java is bonded by static binding and overridden methods are subject to dynamic binding.

5) Private and final method can also be not overridden in Java.

By the way, you might have heard about "a picture is worth more than thousand words" and this is made true by following image. By looking at the pic you can clearly understand difference between method overloading and overriding in Java. 
Difference between Overloading and Overriding in Java


Handling Exception while overloading and overriding method in Java

While overriding a method it can only throw checked exception declared by by overridden method or any subclass of it, means if overridden method throws IOExcpetion than overriding method can throw sub classes of IOExcpetion e.g. FileNotFoundException but not wider exception e.g. Exception or Throwable. This restriction is only for checked Exception for RuntimeException you can throw any RuntimeException. Overloaded method in Java doesn't have such restriction and you are free to modify throws clause as per your need.



Method Overloading and Overriding Example in Java

Here is an example of both method overloading and method overriding in Java. In order to explain the concept we have create two classes Loan and PersonalLoan. createLoan() method is overloaded as it has different version with different signature, while toString() method which is original declared in Object class is overridden in both Loan and PersonalLoan class.

public class OverloadingOverridingTest {

    public static void main(String[] args) {

        // Example of method overloading in Java
        Loan cheapLoan = Loan.createLoan("HSBC");
        Loan veryCheapLoan = Loan.createLoan("Citibank", 8.5);

        // Example of method overriding in Java
        Loan personalLoan = new PersonalLoan();
        personalLoan.toString();
    }

}

public class Loan {
    private double interestRate;
    private String customer;
    private String lender;

    public static Loan createLoan(String lender) {
        Loan loan = new Loan();
        loan.lender = lender;
        return loan;
    }

    public static Loan createLoan(String lender, double interestRate) {
        Loan loan = new Loan();
        loan.lender = lender;
        loan.interestRate = interestRate;
        return loan;
    }

    @Override
    public String toString() {
        return "This is Loan by Citibank";
    }

}

public class PersonalLoan extends Loan {

    @Override
    public String toString() {
        return "This is Personal Loan by Citibank";
    }
}


Things to Remember

1) In case of method overloading method signature gets changed while in case of overriding signature remains same.

2) Return type is not part of method signature in Java.

3) Overloaded method can be subject to compile time binding but overridden method can only be bind at run-time.

4) Both overloaded and overridden method has same name in Java.

5) Static method can not be overridden in Java.

6) Since private method is also not visible outside of class, it can not be overridden and method binding happens during compile time.

7) From Java 5 onwards you can use annotation in Java to declare overridden method just like we did with @override. @override annotation allows compiler, IDE like NetBeans and Eclipse to cross verify or check if this method is really overrides super class method or not.



Covariant Method Overriding in Java

One of my reader Rajeev makes an interesting comment about one change related to return type of overriding method from Java 5 onwards, which enable to use subtype of return type of overridden method. This is really useful, when original method returns a general type like java.lang.Object. If you areoverriding clone() method in Java then you can use this feature to return actual type, instead of returning java.lang.Object and can save caller from type-casting cloned object. Here is the actual comment from Rajeev:


Hi Javin,I visit your blog regularly and I found that you missed covariant return which is added in Java 5 in the case of method overriding. When a subclass wants to change the method implementation of an inherited method (an override), the subclass must define a method that matches the inherited version exactly. Or, as of Java 5, you're allowed to change the return type in the overriding method as long as the new return type is a subtype of the declared return type of the overridden (super class) method. Let's look at a covariant return in action:

class Alpha {
    Alpha doStuff(char c) {
        return new Alpha();
    }
}

class Beta extends Alpha {
    Beta doStuff(char c) { // legal override in Java 1.5
        return new Beta();
    }
}

You can see that Beta class which is overriding doStuff() method from Alpha class is returning Beta type and not Alpha type. This will remove type casting on client side. See here to learn more about covariant method overriding in Java.


AS I said one of the good example of this is overriding clone method and using return type as Actual type instead of java.lang.Object, which is suggested by Joshua Bloch in Effective Java as well. This in in-fact one of the Java best practices while implementing clone method in Java. By the way don't forget to follow these Java overloading best practices, when doing it in your project.
Posted by Javin Paul  
    
Labels: core java , core java interview question
Location: United States

16 comments :

Anonymous said...
what about the exceptions while overriding and overloading
January 4, 2012 at 7:50 PM
Javin @ spring interview questions answers said...
Good point, I have added one section regarding exception handling for overloading and overriding methods in java. thanks for pointing this.
January 5, 2012 at 3:51 AM
Rajeev said...
Hi Javin,I visit your blog regularly and I found that you missed covariant return which is added in Java5 in the case of method overriding.
When a subclass wants to change the method implementation of an inherited method (an override), the subclass must define a method that matches the inherited
version exactly. Or, as of Java 5, you're allowed to change the return type in the
overriding method as long as the new return type is a subtype of the declared return
type of the overridden (superclass) method.
Let's look at a covariant return in action:
class Alpha {
Alpha doStuff(char c) {
return new Alpha();
}
}
class Beta extends Alpha {
Beta doStuff(char c) { // legal override in Java 1.5
return new Beta();
}
}
May 4, 2012 at 5:01 AM
Anonymous said...
to add on what you have described, overloading is done in two steps, first JVM finds all the methods which are applicable for a given type of argument and than in second step it pick the most specific method. for exmaple if you have two method one which takes Object clas as parameter and other takes String class as parameter like below

public void show(Object ob){}
public void show(String str){}

and you call show(null) than since both show() method which are overloaded are applicable but Java will pick the most specific one which is the String version because String is more specific than Object.

Cheers
July 3, 2012 at 9:03 PM
Anonymous said...
Overriding method cannot assign weaker access privileges:
protected in parent
must be kept
public/protected in subclass
August 2, 2012 at 6:25 PM
Anonymous said...
Most simple difference between overloading and overriding in Java is former is a compile time activity while later is a runtime activity. Overloading is fast , overriding is slow. Overloading uses static binding, overriding uses dynamic binding. private, static and final method can be overloaded but can not be overridden.
August 29, 2012 at 9:59 PM
Sunil said...
@Rajiv, Thanks for informing about covariant return type, which allows to change return type of overriding method in Java 1.5, does you can do this only on methods which has Object as return type or its also possible to override a method which has return type long with overriding method has return type primitive int ?
August 29, 2012 at 10:02 PM
Anonymous said...
What is method overloading in Java ?
- multiple method with same name
Why do you need overloading in Java
-because you have method which does same job but with different operands e.g. size() method finding size of Array, Collection and string

When do you use method overloading in Java ?
same as above 
August 31, 2012 at 12:34 AM
Anonymous said...
Example of method overloading and method overriding is not clear to me ? Can you please explain why you overloaded createLoan() method ? Its better you put another example of method overloading and overriding which makes more sense and easy to understand.
September 10, 2012 at 3:17 AM
shweta said...
i m able to override public static method



class TestB{

public static void mytest()
{
System.out.println("ok in B");
}
}
public class TestA extends TestB{
public static void mytest()
{
System.out.println("ok in A");
}

public static void main(String args[])
{
mytest();
}
}
September 27, 2012 at 7:00 AM
Vishal said...
Why people compare method overloading to method overriding ? I thing both are completely different operations except similarity in name. Comparing overloading vs overriding is like comparing Orange to apples.
January 8, 2013 at 6:19 PM
Vivek Hingorani said...
@Shweta: Its not overriding as you havent created any instance and directly calling mytest() from class TestA so it will print "Ok in A" as overriding doesnt come into picture at all..
@Javin: Do let me know if i am wrong :-)
April 13, 2013 at 12:48 AM
kinjal shah said...
I was asked in an interview if we can overload public static void main(String[] args) method?
ans: Yes we can.
May 9, 2013 at 11:55 PM
chetan said...
overloading.....method name remains the same only changes will be in the type or number of arguments

eg: public void testmethod()
public void testmethod(int a,int b)

overriding .....method name and argument remains the same only the implementation will change
for overriding to happen
1>inheritance should happen
eg:

public class test1{

public void test(){
system.out.println("running test method in class test1");
}
}
public class test2 extends test1{

public void test(){
system.out.println("running test method in class test2");
}
}
May 17, 2013 at 3:18 AM
Anonymous said...
Hi Javin, There was a question asked to me in one of the Interviews is- why Overriding method can not throw a broader exception.
November 28, 2014 at 1:51 AM
Anonymous said...
I have been asked twice in interviews that I have attended - What is good about Java and What is Bad about Java ? Could you please throw some light on this ?


Read more: http://javarevisited.blogspot.com/2011/12/method-overloading-vs-method-overriding.html#ixzz3r5JTMTWl
Posted by at No comments:
Subscribe to: Posts (Atom)