com.fitbur.jackson.databind.JsonNode Maven / Gradle / Ivy
package com.fitbur.jackson.databind;
import java.io.IOException;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.*;
import com.fitbur.jackson.core.*;
import com.fitbur.jackson.databind.node.JsonNodeType;
import com.fitbur.jackson.databind.node.MissingNode;
import com.fitbur.jackson.databind.util.ClassUtil;
/**
* Base class for all JSON nodes, which form the basis of JSON
* Tree Model that Jackson implements.
* One way to think of these nodes is to consider them
* similar to DOM nodes in XML DOM trees.
*
* As a general design rule, most accessors ("getters") are included
* in this base class, to allow for traversing structure without
* type casts. Most mutators, however, need to be accessed through
* specific sub-classes (such as ObjectNode
* and ArrayNode).
* This seems sensible because proper type
* information is generally available when building or modifying
* trees, but less often when reading a tree (newly built from
* parsed JSON content).
*
* Actual concrete sub-classes can be found from package
* {@link com.fitbur.jackson.databind.node}.
*
* Note that it is possible to "read" from nodes, using
* method {@link TreeNode#traverse(ObjectCodec)}, which will result in
* a {@link JsonParser} being constructed. This can be used for (relatively)
* efficient conversations between different representations; and it is what
* core databind uses for methods like {@link ObjectMapper#treeToValue(TreeNode, Class)}
* and {@link ObjectMapper#treeAsTokens(TreeNode)}
*/
public abstract class JsonNode
extends JsonSerializable.Base // i.e. implements JsonSerializable
implements TreeNode, Iterable
{
/*
/**********************************************************
/* Construction, related
/**********************************************************
*/
protected JsonNode() { }
/**
* Method that can be called to get a node that is guaranteed
* not to allow changing of this node through mutators on
* this node or any of its children.
* This means it can either make a copy of this node (and all
* mutable children and grand children nodes), or node itself
* if it is immutable.
*
* Note: return type is guaranteed to have same type as the
* node method is called on; which is why method is declared
* with local generic type.
*
* @since 2.0
*
* @return Node that is either a copy of this node (and all non-leaf
* children); or, for immutable leaf nodes, node itself.
*/
public abstract T deepCopy();
/*
/**********************************************************
/* TreeNode implementation
/**********************************************************
*/
// public abstract JsonToken asToken();
// public abstract JsonToken traverse();
// public abstract JsonToken traverse(ObjectCodec codec);
// public abstract JsonParser.NumberType numberType();
@Override
public int size() { return 0; }
@Override
public final boolean isValueNode()
{
switch (getNodeType()) {
case ARRAY: case OBJECT: case MISSING:
return false;
default:
return true;
}
}
@Override
public final boolean isContainerNode() {
final JsonNodeType type = getNodeType();
return type == JsonNodeType.OBJECT || type == JsonNodeType.ARRAY;
}
@Override
public final boolean isMissingNode() {
return getNodeType() == JsonNodeType.MISSING;
}
@Override
public final boolean isArray() {
return getNodeType() == JsonNodeType.ARRAY;
}
@Override
public final boolean isObject() {
return getNodeType() == JsonNodeType.OBJECT;
}
/**
* Method for accessing value of the specified element of
* an array node. For other nodes, null is always returned.
*
* For array nodes, index specifies
* exact location within array and allows for efficient iteration
* over child elements (underlying storage is guaranteed to
* be efficiently indexable, i.e. has random-access to elements).
* If index is less than 0, or equal-or-greater than
* node.size(), null is returned; no exception is
* thrown for any index.
*
* NOTE: if the element value has been explicitly set as null
* (which is different from removal!),
* a {@link com.fitbur.jackson.databind.node.NullNode} will be returned,
* not null.
*
* @return Node that represent value of the specified element,
* if this node is an array and has specified element.
* Null otherwise.
*/
@Override
public abstract JsonNode get(int index);
/**
* Method for accessing value of the specified field of
* an object node. If this node is not an object (or it
* does not have a value for specified field name), or
* if there is no field with such name, null is returned.
*
* NOTE: if the property value has been explicitly set as null
* (which is different from removal!),
* a {@link com.fitbur.jackson.databind.node.NullNode} will be returned,
* not null.
*
* @return Node that represent value of the specified field,
* if this node is an object and has value for the specified
* field. Null otherwise.
*/
@Override
public JsonNode get(String fieldName) { return null; }
/**
* This method is similar to {@link #get(String)}, except
* that instead of returning null if no such value exists (due
* to this node not being an object, or object not having value
* for the specified field),
* a "missing node" (node that returns true for
* {@link #isMissingNode}) will be returned. This allows for
* convenient and safe chained access via path calls.
*/
@Override
public abstract JsonNode path(String fieldName);
/**
* This method is similar to {@link #get(int)}, except
* that instead of returning null if no such element exists (due
* to index being out of range, or this node not being an array),
* a "missing node" (node that returns true for
* {@link #isMissingNode}) will be returned. This allows for
* convenient and safe chained access via path calls.
*/
@Override
public abstract JsonNode path(int index);
@Override
public Iterator fieldNames() {
return ClassUtil.emptyIterator();
}
/**
* Method for locating node specified by given JSON pointer instances.
* Method will never return null; if no matching node exists,
* will return a node for which {@link #isMissingNode()} returns true.
*
* @return Node that matches given JSON Pointer: if no match exists,
* will return a node for which {@link #isMissingNode()} returns true.
*
* @since 2.3
*/
@Override
public final JsonNode at(JsonPointer ptr)
{
// Basically: value nodes only match if we have "empty" path left
if (ptr.matches()) {
return this;
}
JsonNode n = _at(ptr);
if (n == null) {
return MissingNode.getInstance();
}
return n.at(ptr.tail());
}
/**
* Convenience method that is functionally equivalent to:
*
* return at(JsonPointer.valueOf(jsonPointerExpression));
*
*
* Note that if the same expression is used often, it is preferable to construct
* {@link JsonPointer} instance once and reuse it: this method will not perform
* any caching of compiled expressions.
*
* @param jsonPtrExpr Expression to compile as a {@link JsonPointer}
* instance
*
* @return Node that matches given JSON Pointer: if no match exists,
* will return a node for which {@link TreeNode#isMissingNode()} returns true.
*
* @since 2.3
*/
@Override
public final JsonNode at(String jsonPtrExpr) {
return at(JsonPointer.compile(jsonPtrExpr));
}
protected abstract JsonNode _at(JsonPointer ptr);
/*
/**********************************************************
/* Public API, type introspection
/**********************************************************
*/
// // First high-level division between values, containers and "missing"
/**
* Return the type of this node
*
* @return the node type as a {@link JsonNodeType} enum value
*
* @since 2.2
*/
public abstract JsonNodeType getNodeType();
/**
* Method that can be used to check if the node is a wrapper
* for a POJO ("Plain Old Java Object" aka "bean".
* Returns true only for
* instances of POJONode.
*
* @return True if this node wraps a POJO
*/
public final boolean isPojo() {
return getNodeType() == JsonNodeType.POJO;
}
/**
* @return True if this node represents a numeric JSON value
*/
public final boolean isNumber() {
return getNodeType() == JsonNodeType.NUMBER;
}
/**
*
* @return True if this node represents an integral (integer)
* numeric JSON value
*/
public boolean isIntegralNumber() { return false; }
/**
* @return True if this node represents a non-integral
* numeric JSON value
*/
public boolean isFloatingPointNumber() { return false; }
/**
* Method that can be used to check whether contained value
* is a number represented as Java short.
* Note, however, that even if this method returns false, it
* is possible that conversion would be possible from other numeric
* types -- to check if this is possible, use
* {@link #canConvertToInt()} instead.
*
* @return True if the value contained by this node is stored as Java short
*/
public boolean isShort() { return false; }
/**
* Method that can be used to check whether contained value
* is a number represented as Java int.
* Note, however, that even if this method returns false, it
* is possible that conversion would be possible from other numeric
* types -- to check if this is possible, use
* {@link #canConvertToInt()} instead.
*
* @return True if the value contained by this node is stored as Java int
*/
public boolean isInt() { return false; }
/**
* Method that can be used to check whether contained value
* is a number represented as Java long.
* Note, however, that even if this method returns false, it
* is possible that conversion would be possible from other numeric
* types -- to check if this is possible, use
* {@link #canConvertToInt()} instead.
*
* @return True if the value contained by this node is stored as Java long
*/
public boolean isLong() { return false; }
/**
* @since 2.2
*/
public boolean isFloat() { return false; }
public boolean isDouble() { return false; }
public boolean isBigDecimal() { return false; }
public boolean isBigInteger() { return false; }
/**
* Method that checks whether this node represents basic JSON String
* value.
*/
public final boolean isTextual() {
return getNodeType() == JsonNodeType.STRING;
}
/**
* Method that can be used to check if this node was created from
* JSON boolean value (literals "true" and "false").
*/
public final boolean isBoolean() {
return getNodeType() == JsonNodeType.BOOLEAN;
}
/**
* Method that can be used to check if this node was created from
* JSON literal null value.
*/
public final boolean isNull() {
return getNodeType() == JsonNodeType.NULL;
}
/**
* Method that can be used to check if this node represents
* binary data (Base64 encoded). Although this will be externally
* written as JSON String value, {@link #isTextual} will
* return false if this method returns true.
*
* @return True if this node represents base64 encoded binary data
*/
public final boolean isBinary() {
return getNodeType() == JsonNodeType.BINARY;
}
/**
* Method that can be used to check whether this node is a numeric
* node ({@link #isNumber} would return true) AND its value fits
* within Java's 32-bit signed integer type, int.
* Note that floating-point numbers are convertible if the integral
* part fits without overflow (as per standard Java coercion rules)
*
* NOTE: this method does not consider possible value type conversion
* from JSON String into Number; so even if this method returns false,
* it is possible that {@link #asInt} could still succeed
* if node is a JSON String representing integral number, or boolean.
*
* @since 2.0
*/
public boolean canConvertToInt() { return false; }
/**
* Method that can be used to check whether this node is a numeric
* node ({@link #isNumber} would return true) AND its value fits
* within Java's 64-bit signed integer type, long.
* Note that floating-point numbers are convertible if the integral
* part fits without overflow (as per standard Java coercion rules)
*
* NOTE: this method does not consider possible value type conversion
* from JSON String into Number; so even if this method returns false,
* it is possible that {@link #asLong} could still succeed
* if node is a JSON String representing integral number, or boolean.
*
* @since 2.0
*/
public boolean canConvertToLong() { return false; }
/*
/**********************************************************
/* Public API, straight value access
/**********************************************************
*/
/**
* Method to use for accessing String values.
* Does NOT do any conversions for non-String value nodes;
* for non-String values (ones for which {@link #isTextual} returns
* false) null will be returned.
* For String values, null is never returned (but empty Strings may be)
*
* @return Textual value this node contains, iff it is a textual
* JSON node (comes from JSON String value entry)
*/
public String textValue() { return null; }
/**
* Method to use for accessing binary content of binary nodes (nodes
* for which {@link #isBinary} returns true); or for Text Nodes
* (ones for which {@link #textValue} returns non-null value),
* to read decoded base64 data.
* For other types of nodes, returns null.
*
* @return Binary data this node contains, iff it is a binary
* node; null otherwise
*/
public byte[] binaryValue() throws IOException {
return null;
}
/**
* Method to use for accessing JSON boolean values (value
* literals 'true' and 'false').
* For other types, always returns false.
*
* @return Textual value this node contains, iff it is a textual
* json node (comes from JSON String value entry)
*/
public boolean booleanValue() { return false; }
/**
* Returns numeric value for this node, if and only if
* this node is numeric ({@link #isNumber} returns true); otherwise
* returns null
*
* @return Number value this node contains, if any (null for non-number
* nodes).
*/
public Number numberValue() { return null; }
/**
* Returns 16-bit short value for this node, if and only if
* this node is numeric ({@link #isNumber} returns true). For other
* types returns 0.
* For floating-point numbers, value is truncated using default
* Java coercion, similar to how cast from double to short operates.
*
* @return Short value this node contains, if any; 0 for non-number
* nodes.
*/
public short shortValue() { return 0; }
/**
* Returns integer value for this node, if and only if
* this node is numeric ({@link #isNumber} returns true). For other
* types returns 0.
* For floating-point numbers, value is truncated using default
* Java coercion, similar to how cast from double to int operates.
*
* @return Integer value this node contains, if any; 0 for non-number
* nodes.
*/
public int intValue() { return 0; }
/**
* Returns 64-bit long value for this node, if and only if
* this node is numeric ({@link #isNumber} returns true). For other
* types returns 0.
* For floating-point numbers, value is truncated using default
* Java coercion, similar to how cast from double to long operates.
*
* @return Long value this node contains, if any; 0 for non-number
* nodes.
*/
public long longValue() { return 0L; }
/**
* Returns 32-bit floating value for this node, if and only if
* this node is numeric ({@link #isNumber} returns true). For other
* types returns 0.0.
* For integer values, conversion is done using coercion; this means
* that an overflow is possible for `long` values
*
* @return 32-bit float value this node contains, if any; 0.0 for non-number nodes.
*
* @since 2.2
*/
public float floatValue() { return 0.0f; }
/**
* Returns 64-bit floating point (double) value for this node, if and only if
* this node is numeric ({@link #isNumber} returns true). For other
* types returns 0.0.
* For integer values, conversion is done using coercion; this may result
* in overflows with {@link BigInteger} values.
*
* @return 64-bit double value this node contains, if any; 0.0 for non-number nodes.
*
* @since 2.2
*/
public double doubleValue() { return 0.0; }
public BigDecimal decimalValue() { return BigDecimal.ZERO; }
public BigInteger bigIntegerValue() { return BigInteger.ZERO; }
/*
/**********************************************************
/* Public API, value access with conversion(s)/coercion(s)
/**********************************************************
*/
/**
* Method that will return a valid String representation of
* the container value, if the node is a value node
* (method {@link #isValueNode} returns true),
* otherwise empty String.
*/
public abstract String asText();
/**
* Method similar to {@link #asText()}, except that it will return
* defaultValue in cases where null value would be returned;
* either for missing nodes (trying to access missing property, or element
* at invalid item for array) or explicit nulls.
*
* @since 2.4
*/
public String asText(String defaultValue) {
String str = asText();
return (str == null) ? defaultValue : str;
}
/**
* Method that will try to convert value of this node to a Java int.
* Numbers are coerced using default Java rules; booleans convert to 0 (false)
* and 1 (true), and Strings are parsed using default Java language integer
* parsing rules.
*
* If representation can not be converted to an int (including structured types
* like Objects and Arrays),
* default value of 0 will be returned; no exceptions are thrown.
*/
public int asInt() {
return asInt(0);
}
/**
* Method that will try to convert value of this node to a Java int.
* Numbers are coerced using default Java rules; booleans convert to 0 (false)
* and 1 (true), and Strings are parsed using default Java language integer
* parsing rules.
*
* If representation can not be converted to an int (including structured types
* like Objects and Arrays),
* specified defaultValue will be returned; no exceptions are thrown.
*/
public int asInt(int defaultValue) {
return defaultValue;
}
/**
* Method that will try to convert value of this node to a Java long.
* Numbers are coerced using default Java rules; booleans convert to 0 (false)
* and 1 (true), and Strings are parsed using default Java language integer
* parsing rules.
*
* If representation can not be converted to an long (including structured types
* like Objects and Arrays),
* default value of 0 will be returned; no exceptions are thrown.
*/
public long asLong() {
return asLong(0L);
}
/**
* Method that will try to convert value of this node to a Java long.
* Numbers are coerced using default Java rules; booleans convert to 0 (false)
* and 1 (true), and Strings are parsed using default Java language integer
* parsing rules.
*
* If representation can not be converted to an long (including structured types
* like Objects and Arrays),
* specified defaultValue will be returned; no exceptions are thrown.
*/
public long asLong(long defaultValue) {
return defaultValue;
}
/**
* Method that will try to convert value of this node to a Java double.
* Numbers are coerced using default Java rules; booleans convert to 0.0 (false)
* and 1.0 (true), and Strings are parsed using default Java language integer
* parsing rules.
*
* If representation can not be converted to an int (including structured types
* like Objects and Arrays),
* default value of 0.0 will be returned; no exceptions are thrown.
*/
public double asDouble() {
return asDouble(0.0);
}
/**
* Method that will try to convert value of this node to a Java double.
* Numbers are coerced using default Java rules; booleans convert to 0.0 (false)
* and 1.0 (true), and Strings are parsed using default Java language integer
* parsing rules.
*
* If representation can not be converted to an int (including structured types
* like Objects and Arrays),
* specified defaultValue will be returned; no exceptions are thrown.
*/
public double asDouble(double defaultValue) {
return defaultValue;
}
/**
* Method that will try to convert value of this node to a Java boolean.
* JSON booleans map naturally; integer numbers other than 0 map to true, and
* 0 maps to false
* and Strings 'true' and 'false' map to corresponding values.
*
* If representation can not be converted to a boolean value (including structured types
* like Objects and Arrays),
* default value of false will be returned; no exceptions are thrown.
*/
public boolean asBoolean() {
return asBoolean(false);
}
/**
* Method that will try to convert value of this node to a Java boolean.
* JSON booleans map naturally; integer numbers other than 0 map to true, and
* 0 maps to false
* and Strings 'true' and 'false' map to corresponding values.
*
* If representation can not be converted to a boolean value (including structured types
* like Objects and Arrays),
* specified defaultValue will be returned; no exceptions are thrown.
*/
public boolean asBoolean(boolean defaultValue) {
return defaultValue;
}
/*
/**********************************************************
/* Public API, value find / existence check methods
/**********************************************************
*/
/**
* Method that allows checking whether this node is JSON Object node
* and contains value for specified property. If this is the case
* (including properties with explicit null values), returns true;
* otherwise returns false.
*
* This method is equivalent to:
*
* node.get(fieldName) != null
*
* (since return value of get() is node, not value node contains)
*
* NOTE: when explicit null values are added, this
* method will return true for such properties.
*
* @param fieldName Name of element to check
*
* @return True if this node is a JSON Object node, and has a property
* entry with specified name (with any value, including null value)
*/
public boolean has(String fieldName) {
return get(fieldName) != null;
}
/**
* Method that allows checking whether this node is JSON Array node
* and contains a value for specified index
* If this is the case
* (including case of specified indexing having null as value), returns true;
* otherwise returns false.
*
* Note: array element indexes are 0-based.
*
* This method is equivalent to:
*
* node.get(index) != null
*
*
* NOTE: this method will return true for explicitly added
* null values.
*
* @param index Index to check
*
* @return True if this node is a JSON Object node, and has a property
* entry with specified name (with any value, including null value)
*/
public boolean has(int index) {
return get(index) != null;
}
/**
* Method that is similar to {@link #has(String)}, but that will
* return false for explicitly added nulls.
*
* This method is functionally equivalent to:
*
* node.get(fieldName) != null << !node.get(fieldName).isNull()
*
*
* @since 2.1
*/
public boolean hasNonNull(String fieldName) {
JsonNode n = get(fieldName);
return (n != null) && !n.isNull();
}
/**
* Method that is similar to {@link #has(int)}, but that will
* return false for explicitly added nulls.
*
* This method is equivalent to:
*
* node.get(index) != null << !node.get(index).isNull()
*
*
* @since 2.1
*/
public boolean hasNonNull(int index) {
JsonNode n = get(index);
return (n != null) && !n.isNull();
}
/*
/**********************************************************
/* Public API, container access
/**********************************************************
*/
/**
* Same as calling {@link #elements}; implemented so that
* convenience "for-each" loop can be used for looping over elements
* of JSON Array constructs.
*/
@Override
public final Iterator iterator() { return elements(); }
/**
* Method for accessing all value nodes of this Node, iff
* this node is a JSON Array or Object node. In case of Object node,
* field names (keys) are not included, only values.
* For other types of nodes, returns empty iterator.
*/
public Iterator elements() {
return ClassUtil.emptyIterator();
}
/**
* @return Iterator that can be used to traverse all key/value pairs for
* object nodes; empty iterator (no contents) for other types
*/
public Iterator> fields() {
return ClassUtil.emptyIterator();
}
/*
/**********************************************************
/* Public API, find methods
/**********************************************************
*/
/**
* Method for finding a JSON Object field with specified name in this
* node or its child nodes, and returning value it has.
* If no matching field is found in this node or its descendants, returns null.
*
* @param fieldName Name of field to look for
*
* @return Value of first matching node found, if any; null if none
*/
public abstract JsonNode findValue(String fieldName);
/**
* Method for finding JSON Object fields with specified name, and returning
* found ones as a List. Note that sub-tree search ends if a field is found,
* so possible children of result nodes are not included.
* If no matching fields are found in this node or its descendants, returns
* an empty List.
*
* @param fieldName Name of field to look for
*/
public final List findValues(String fieldName)
{
List result = findValues(fieldName, null);
if (result == null) {
return Collections.emptyList();
}
return result;
}
/**
* Similar to {@link #findValues}, but will additionally convert
* values into Strings, calling {@link #asText}.
*/
public final List findValuesAsText(String fieldName)
{
List result = findValuesAsText(fieldName, null);
if (result == null) {
return Collections.emptyList();
}
return result;
}
/**
* Method similar to {@link #findValue}, but that will return a
* "missing node" instead of null if no field is found. Missing node
* is a specific kind of node for which {@link #isMissingNode}
* returns true; and all value access methods return empty or
* missing value.
*
* @param fieldName Name of field to look for
*
* @return Value of first matching node found; or if not found, a
* "missing node" (non-null instance that has no value)
*/
public abstract JsonNode findPath(String fieldName);
/**
* Method for finding a JSON Object that contains specified field,
* within this node or its descendants.
* If no matching field is found in this node or its descendants, returns null.
*
* @param fieldName Name of field to look for
*
* @return Value of first matching node found, if any; null if none
*/
public abstract JsonNode findParent(String fieldName);
/**
* Method for finding a JSON Object that contains specified field,
* within this node or its descendants.
* If no matching field is found in this node or its descendants, returns null.
*
* @param fieldName Name of field to look for
*
* @return Value of first matching node found, if any; null if none
*/
public final List findParents(String fieldName)
{
List result = findParents(fieldName, null);
if (result == null) {
return Collections.emptyList();
}
return result;
}
public abstract List findValues(String fieldName, List foundSoFar);
public abstract List findValuesAsText(String fieldName, List foundSoFar);
public abstract List findParents(String fieldName, List foundSoFar);
/*
/**********************************************************
/* Public API, path handling
/**********************************************************
*/
/**
* Method that can be called on Object nodes, to access a property
* that has Object value; or if no such property exists, to create,
* add and return such Object node.
* If the node method is called on is not Object node,
* or if property exists and has value that is not Object node,
* {@link UnsupportedOperationException} is thrown
*/
public JsonNode with(String propertyName) {
throw new UnsupportedOperationException("JsonNode not of type ObjectNode (but "
+getClass().getName()+"), can not call with() on it");
}
/**
* Method that can be called on Object nodes, to access a property
* that has Array value; or if no such property exists, to create,
* add and return such Array node.
* If the node method is called on is not Object node,
* or if property exists and has value that is not Array node,
* {@link UnsupportedOperationException} is thrown
*/
public JsonNode withArray(String propertyName) {
throw new UnsupportedOperationException("JsonNode not of type ObjectNode (but "
+getClass().getName()+"), can not call withArray() on it");
}
/*
/**********************************************************
/* Public API, comparison
/**********************************************************
*/
/**
* Entry method for invoking customizable comparison, using passed-in
* {@link Comparator} object. Nodes will handle traversal of structured
* types (arrays, objects), but defer to comparator for scalar value
* comparisons. If a "natural" {@link Comparator} is passed -- one that
* simply calls equals() on one of arguments, passing the other
* -- implementation is the same as directly calling equals()
* on node.
*
* Default implementation simply delegates to passed in comparator,
* with this as the first argument, and other as
* the second argument.
*
* @param comparator Object called to compare two scalar {@link JsonNode}
* instances, and return either 0 (are equals) or non-zero (not equal)
*
* @since 2.6
*/
public boolean equals(Comparator comparator, JsonNode other) {
return comparator.compare(this, other) == 0;
}
/*
/**********************************************************
/* Overridden standard methods
/**********************************************************
*/
/**
* Method that will produce developer-readable representation of the
* node; which may or may not be as valid JSON.
* If you want valid JSON output (or output formatted using one of
* other Jackson supported data formats) make sure to use
* {@link ObjectMapper} or {@link ObjectWriter} to serialize an
* instance, for example:
*
* String json = objectMapper.writeValueAsString(rootNode);
*
*
* Note: method defined as abstract to ensure all implementation
* classes explicitly implement method, instead of relying
* on {@link Object#toString()} definition.
*/
@Override
public abstract String toString();
/**
* Equality for node objects is defined as full (deep) value
* equality. This means that it is possible to compare complete
* JSON trees for equality by comparing equality of root nodes.
*
* Note: marked as abstract to ensure all implementation
* classes define it properly and not rely on definition
* from {@link java.lang.Object}.
*/
@Override
public abstract boolean equals(Object o);
}