# Class DefaultMutableTreeNode

java.lang.Object
javax.swing.tree.DefaultMutableTreeNode

All Implemented Interfaces:
  `Serializable, Cloneable, MutableTreeNode, TreeNode`

Direct Known Subclasses:
  `JTree.DynamicUtilTreeNode`

public class DefaultMutableTreeNode extends Object implements Cloneable, MutableTreeNode, Serializable
A `DefaultMutableTreeNode` is a general-purpose node in a tree data structure. For examples of using default mutable tree nodes, see How to Use Trees in The Java Tutorial.

A tree node may have at most one parent and 0 or more children. `DefaultMutableTreeNode` provides operations for examining and modifying a node's parent and children and also operations for examining the tree that the node is a part of. A node's tree is the set of all nodes that can be reached by starting at the node and following all the possible links to parents and children. A node with no parent is the root of its tree; a node with no children is a leaf. A tree may consist of many subtrees, each node acting as the root for its own subtree.

This class provides enumerations for efficiently traversing a tree or subtree in various orders or for following the path between two nodes. A `DefaultMutableTreeNode` may also hold a reference to a user object, the use of which is left to the user. Asking a `DefaultMutableTreeNode` for its string representation with `toString()` returns the string representation of its user object.

This is not a thread safe class.If you intend to use a DefaultMutableTreeNode (or a tree of TreeNodes) in more than one thread, you need to do your own synchronizing. A good convention to adopt is synchronizing on the root node of a tree.

While DefaultMutableTreeNode implements the MutableTreeNode interface and will allow you to add in any implementation of MutableTreeNode not all of the methods in DefaultMutableTreeNode will be applicable to all MutableTreeNodes implementations. Especially with some of the enumerations that are provided, using some of these methods assumes the DefaultMutableTreeNode contains only DefaultMutableNode instances. All of the TreeNode/MutableTreeNode methods will behave as defined no matter what implementations are added.

Warning: Serialized objects of this class will not be compatible with future Swing releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Swing. As of 1.4, support for long term storage of all JavaBeans has been added to the `java.beans` package. Please see `XMLEncoder`.

See Also:
  - `MutableTreeNode`

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected boolean`
  `allowsChildren`
  true if the node is able to have children
  `protected Vector<TreeNode>`
  `children`
  array of children, may be null if this node has no children
  `static final Enumeration<TreeNode>`
  `EMPTY_ENUMERATION`
  An enumeration that is always empty.
  `protected MutableTreeNode`
  `parent`
  this node's parent, or null if this node has no parent
  `protected Object`
  `userObject`
  optional user object

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `DefaultMutableTreeNode()`
  Creates a tree node that has no parent and no children, but which allows children.
  `DefaultMutableTreeNode(Object userObject)`
  Creates a tree node with no parent, no children, but which allows children, and initializes it with the specified user object.
  `DefaultMutableTreeNode(Object userObject, boolean allowsChildren)`
  Creates a tree node with no parent, no children, initialized with the specified user object, and that allows children only if specified.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `add(MutableTreeNode newChild)`
  Removes `newChild` from its parent and makes it a child of this node by adding it to the end of this node's child array.
  `Enumeration<TreeNode>`
  `breadthFirstEnumeration()`
  Creates and returns an enumeration that traverses the subtree rooted at this node in breadth-first order.
  `Enumeration<TreeNode>`
  `children()`
  Creates and returns a forward-order enumeration of this node's children.
  `Object`
  `clone()`
  Overridden to make clone public.
  `Enumeration<TreeNode>`
  `depthFirstEnumeration()`
  Creates and returns an enumeration that traverses the subtree rooted at this node in depth-first order.
  `boolean`
  `getAllowsChildren()`
  Returns true if this node is allowed to have children.
  `TreeNode`
  `getChildAfter(TreeNode aChild)`
  Returns the child in this node's child array that immediately follows `aChild`, which must be a child of this node.
  `TreeNode`
  `getChildAt(int index)`
  Returns the child at the specified index in this node's child array.
  `TreeNode`
  `getChildBefore(TreeNode aChild)`
  Returns the child in this node's child array that immediately precedes `aChild`, which must be a child of this node.
  `int`
  `getChildCount()`
  Returns the number of children of this node.
  `int`
  `getDepth()`
  Returns the depth of the tree rooted at this node -- the longest distance from this node to a leaf.
  `TreeNode`
  `getFirstChild()`
  Returns this node's first child.
  `DefaultMutableTreeNode`
  `getFirstLeaf()`
  Finds and returns the first leaf that is a descendant of this node -- either this node or its first child's first leaf.
  `int`
  `getIndex(TreeNode aChild)`
  Returns the index of the specified child in this node's child array.
  `TreeNode`
  `getLastChild()`
  Returns this node's last child.
  `DefaultMutableTreeNode`
  `getLastLeaf()`
  Finds and returns the last leaf that is a descendant of this node -- either this node or its last child's last leaf.
  `int`
  `getLeafCount()`
  Returns the total number of leaves that are descendants of this node.
  `int`
  `getLevel()`
  Returns the number of levels above this node -- the distance from the root to this node.
  `DefaultMutableTreeNode`
  `getNextLeaf()`
  Returns the leaf after this node or null if this node is the last leaf in the tree.
  `DefaultMutableTreeNode`
  `getNextNode()`
  Returns the node that follows this node in a preorder traversal of this node's tree.
  `DefaultMutableTreeNode`
  `getNextSibling()`
  Returns the next sibling of this node in the parent's children array.
  `TreeNode`
  `getParent()`
  Returns this node's parent or null if this node has no parent.
  `TreeNode[]`
  `getPath()`
  Returns the path from the root, to get to this node.
  `protected TreeNode[]`
  `getPathToRoot(TreeNode aNode, int depth)`
  Builds the parents of node up to and including the root node, where the original node is the last element in the returned array.
  `DefaultMutableTreeNode`
  `getPreviousLeaf()`
  Returns the leaf before this node or null if this node is the first leaf in the tree.
  `DefaultMutableTreeNode`
  `getPreviousNode()`
  Returns the node that precedes this node in a preorder traversal of this node's tree.
  `DefaultMutableTreeNode`
  `getPreviousSibling()`
  Returns the previous sibling of this node in the parent's children array.
  `TreeNode`
  `getRoot()`
  Returns the root of the tree that contains this node.
  `TreeNode`
  `getSharedAncestor(DefaultMutableTreeNode aNode)`
  Returns the nearest common ancestor to this node and `aNode`.
  `int`
  `getSiblingCount()`
  Returns the number of siblings of this node.
  `Object`
  `getUserObject()`
  Returns this node's user object.
  `Object[]`
  `getUserObjectPath()`
  Returns the user object path, from the root, to get to this node.
  `void`
  `insert(MutableTreeNode newChild, int childIndex)`
  Removes `newChild` from its present parent (if it has a parent), sets the child's parent to this node, and then adds the child to this node's child array at index `childIndex`.
  `boolean`
  `isLeaf()`
  Returns true if this node has no children.
  `boolean`
  `isNodeAncestor(TreeNode anotherNode)`
  Returns true if `anotherNode` is an ancestor of this node -- if it is this node, this node's parent, or an ancestor of this node's parent.
  `boolean`
  `isNodeChild(TreeNode aNode)`
  Returns true if `aNode` is a child of this node.
  `boolean`
  `isNodeDescendant(DefaultMutableTreeNode anotherNode)`
  Returns true if `anotherNode` is a descendant of this node -- if it is this node, one of this node's children, or a descendant of one of this node's children.
  `boolean`
  `isNodeRelated(DefaultMutableTreeNode aNode)`
  Returns true if and only if `aNode` is in the same tree as this node.
  `boolean`
  `isNodeSibling(TreeNode anotherNode)`
  Returns true if `anotherNode` is a sibling of (has the same parent as) this node.
  `boolean`
  `isRoot()`
  Returns true if this node is the root of the tree.
  `Enumeration<TreeNode>`
  `pathFromAncestorEnumeration(TreeNode ancestor)`
  Creates and returns an enumeration that follows the path from `ancestor` to this node.
  `Enumeration<TreeNode>`
  `postorderEnumeration()`
  Creates and returns an enumeration that traverses the subtree rooted at this node in postorder.
  `Enumeration<TreeNode>`
  `preorderEnumeration()`
  Creates and returns an enumeration that traverses the subtree rooted at this node in preorder.
  `void`
  `remove(int childIndex)`
  Removes the child at the specified index from this node's children and sets that node's parent to null.
  `void`
  `remove(MutableTreeNode aChild)`
  Removes `aChild` from this node's child array, giving it a null parent.
  `void`
  `removeAllChildren()`
  Removes all of this node's children, setting their parents to null.
  `void`
  `removeFromParent()`
  Removes the subtree rooted at this node from the tree, giving this node a null parent.
  `void`
  `setAllowsChildren(boolean allows)`
  Determines whether or not this node is allowed to have children.
  `void`
  `setParent(MutableTreeNode newParent)`
  Sets this node's parent to `newParent` but does not change the parent's child array.
  `void`
  `setUserObject(Object userObject)`
  Sets the user object for this node to `userObject`.
  `String`
  `toString()`
  Returns the result of sending `toString()` to this node's user object, or the empty string if the node has no user object.

  ### Methods declared in class Object

  `equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- ## Field Details

  - ### EMPTY_ENUMERATION

    public static final Enumeration<TreeNode> EMPTY_ENUMERATION
    An enumeration that is always empty. This is used when an enumeration of a leaf node's children is requested.

  - ### parent

    protected MutableTreeNode parent
    this node's parent, or null if this node has no parent

  - ### children

    protected Vector<TreeNode> children
    array of children, may be null if this node has no children

  - ### userObject

    protected transient Object userObject
    optional user object

  - ### allowsChildren

    protected boolean allowsChildren
    true if the node is able to have children

- ## Constructor Details

  - ### DefaultMutableTreeNode

    public DefaultMutableTreeNode()
    Creates a tree node that has no parent and no children, but which allows children.

  - ### DefaultMutableTreeNode

    public DefaultMutableTreeNode(Object userObject)
    Creates a tree node with no parent, no children, but which allows children, and initializes it with the specified user object.
    Parameters:
      `userObject` - an Object provided by the user that constitutes the node's data

  - ### DefaultMutableTreeNode

    public DefaultMutableTreeNode(Object userObject, boolean allowsChildren)
    Creates a tree node with no parent, no children, initialized with the specified user object, and that allows children only if specified.
    Parameters:
      `userObject` - an Object provided by the user that constitutes the node's data
      `allowsChildren` - if true, the node is allowed to have child nodes -- otherwise, it is always a leaf node

- ## Method Details

  - ### insert

    public void insert(MutableTreeNode newChild, int childIndex)
    Removes `newChild` from its present parent (if it has a parent), sets the child's parent to this node, and then adds the child to this node's child array at index `childIndex`. `newChild` must not be null and must not be an ancestor of this node.
    Specified by:
      `insert` in interface `MutableTreeNode`
    Parameters:
      `newChild` - the MutableTreeNode to insert under this node
      `childIndex` - the index in this node's child array where this node is to be inserted
    Throws:
      `ArrayIndexOutOfBoundsException` - if `childIndex` is out of bounds
      `IllegalArgumentException` - if `newChild` is null or is an ancestor of this node
      `IllegalStateException` - if this node does not allow children
    See Also:
      - `isNodeDescendant(DefaultMutableTreeNode)`

  - ### remove

    public void remove(int childIndex)
    Removes the child at the specified index from this node's children and sets that node's parent to null. The child node to remove must be a `MutableTreeNode`.
    Specified by:
      `remove` in interface `MutableTreeNode`
    Parameters:
      `childIndex` - the index in this node's child array of the child to remove
    Throws:
      `ArrayIndexOutOfBoundsException` - if `childIndex` is out of bounds

  - ### setParent

    public void setParent(MutableTreeNode newParent)
    Sets this node's parent to `newParent` but does not change the parent's child array. This method is called from `insert()` and `remove()` to reassign a child's parent, it should not be messaged from anywhere else.
    Specified by:
      `setParent` in interface `MutableTreeNode`
    Parameters:
      `newParent` - this node's new parent

  - ### getParent

    public TreeNode getParent()
    Returns this node's parent or null if this node has no parent.
    Specified by:
      `getParent` in interface `TreeNode`
    Returns:
      this node's parent TreeNode, or null if this node has no parent

  - ### getChildAt

    public TreeNode getChildAt(int index)
    Returns the child at the specified index in this node's child array.
    Specified by:
      `getChildAt` in interface `TreeNode`
    Parameters:
      `index` - an index into this node's child array
    Returns:
      the TreeNode in this node's child array at the specified index
    Throws:
      `ArrayIndexOutOfBoundsException` - if `index` is out of bounds

  - ### getChildCount

    public int getChildCount()
    Returns the number of children of this node.
    Specified by:
      `getChildCount` in interface `TreeNode`
    Returns:
      an int giving the number of children of this node

  - ### getIndex

    public int getIndex(TreeNode aChild)
    Returns the index of the specified child in this node's child array. If the specified node is not a child of this node, returns `-1`. This method performs a linear search and is O(n) where n is the number of children.
    Specified by:
      `getIndex` in interface `TreeNode`
    Parameters:
      `aChild` - the TreeNode to search for among this node's children
    Returns:
      an int giving the index of the node in this node's child array, or `-1` if the specified node is a not a child of this node
    Throws:
      `IllegalArgumentException` - if `aChild` is null

  - ### children

    public Enumeration<TreeNode> children()
    Creates and returns a forward-order enumeration of this node's children. Modifying this node's child array invalidates any child enumerations created before the modification.
    Specified by:
      `children` in interface `TreeNode`
    Returns:
      an Enumeration of this node's children

  - ### setAllowsChildren

    public void setAllowsChildren(boolean allows)
    Determines whether or not this node is allowed to have children. If `allows` is false, all of this node's children are removed.

    Note: By default, a node allows children.

    Parameters:
      `allows` - true if this node is allowed to have children

  - ### getAllowsChildren

    public boolean getAllowsChildren()
    Returns true if this node is allowed to have children.
    Specified by:
      `getAllowsChildren` in interface `TreeNode`
    Returns:
      true if this node allows children, else false

  - ### setUserObject

    public void setUserObject(Object userObject)
    Sets the user object for this node to `userObject`.
    Specified by:
      `setUserObject` in interface `MutableTreeNode`
    Parameters:
      `userObject` - the Object that constitutes this node's user-specified data
    See Also:
      - `getUserObject()`
      - `toString()`

  - ### getUserObject

    public Object getUserObject()
    Returns this node's user object.
    Returns:
      the Object stored at this node by the user
    See Also:
      - `setUserObject(Object)`
      - `toString()`

  - ### removeFromParent

    public void removeFromParent()
    Removes the subtree rooted at this node from the tree, giving this node a null parent. Does nothing if this node is the root of its tree.
    Specified by:
      `removeFromParent` in interface `MutableTreeNode`

  - ### remove

    public void remove(MutableTreeNode aChild)
    Removes `aChild` from this node's child array, giving it a null parent.
    Specified by:
      `remove` in interface `MutableTreeNode`
    Parameters:
      `aChild` - a child of this node to remove
    Throws:
      `IllegalArgumentException` - if `aChild` is null or is not a child of this node

  - ### removeAllChildren

    public void removeAllChildren()
    Removes all of this node's children, setting their parents to null. If this node has no children, this method does nothing.

  - ### add

    public void add(MutableTreeNode newChild)
    Removes `newChild` from its parent and makes it a child of this node by adding it to the end of this node's child array.
    Parameters:
      `newChild` - node to add as a child of this node
    Throws:
      `IllegalArgumentException` - if `newChild` is null
      `IllegalStateException` - if this node does not allow children
    See Also:
      - `insert(MutableTreeNode, int)`

  - ### isNodeAncestor

    public boolean isNodeAncestor(TreeNode anotherNode)
    Returns true if `anotherNode` is an ancestor of this node -- if it is this node, this node's parent, or an ancestor of this node's parent. (Note that a node is considered an ancestor of itself.) If `anotherNode` is null, this method returns false. This operation is at worst O(h) where h is the distance from the root to this node.
    Parameters:
      `anotherNode` - node to test as an ancestor of this node
    Returns:
      true if this node is a descendant of `anotherNode`
    See Also:
      - `isNodeDescendant(DefaultMutableTreeNode)`
      - `getSharedAncestor(DefaultMutableTreeNode)`

  - ### isNodeDescendant

    public boolean isNodeDescendant(DefaultMutableTreeNode anotherNode)
    Returns true if `anotherNode` is a descendant of this node -- if it is this node, one of this node's children, or a descendant of one of this node's children. Note that a node is considered a descendant of itself. If `anotherNode` is null, returns false. This operation is at worst O(h) where h is the distance from the root to `anotherNode`.
    Parameters:
      `anotherNode` - node to test as descendant of this node
    Returns:
      true if this node is an ancestor of `anotherNode`
    See Also:
      - `isNodeAncestor(TreeNode)`
      - `getSharedAncestor(DefaultMutableTreeNode)`

  - ### getSharedAncestor

    public TreeNode getSharedAncestor(DefaultMutableTreeNode aNode)
    Returns the nearest common ancestor to this node and `aNode`. Returns null, if no such ancestor exists -- if this node and `aNode` are in different trees or if `aNode` is null. A node is considered an ancestor of itself.
    Parameters:
      `aNode` - node to find common ancestor with
    Returns:
      nearest ancestor common to this node and `aNode`, or null if none
    See Also:
      - `isNodeAncestor(TreeNode)`
      - `isNodeDescendant(DefaultMutableTreeNode)`

  - ### isNodeRelated

    public boolean isNodeRelated(DefaultMutableTreeNode aNode)
    Returns true if and only if `aNode` is in the same tree as this node. Returns false if `aNode` is null.
    Parameters:
      `aNode` - node to find common ancestor with
    Returns:
      true if `aNode` is in the same tree as this node; false if `aNode` is null
    See Also:
      - `getSharedAncestor(DefaultMutableTreeNode)`
      - `getRoot()`

  - ### getDepth

    public int getDepth()
    Returns the depth of the tree rooted at this node -- the longest distance from this node to a leaf. If this node has no children, returns 0. This operation is much more expensive than `getLevel()` because it must effectively traverse the entire tree rooted at this node.
    Returns:
      the depth of the tree whose root is this node
    See Also:
      - `getLevel()`

  - ### getLevel

    public int getLevel()
    Returns the number of levels above this node -- the distance from the root to this node. If this node is the root, returns 0.
    Returns:
      the number of levels above this node
    See Also:
      - `getDepth()`

  - ### getPath

    public TreeNode[] getPath()
    Returns the path from the root, to get to this node. The last element in the path is this node.
    Returns:
      an array of TreeNode objects giving the path, where the first element in the path is the root and the last element is this node.

  - ### getPathToRoot

    protected TreeNode[] getPathToRoot(TreeNode aNode, int depth)
    Builds the parents of node up to and including the root node, where the original node is the last element in the returned array. The length of the returned array gives the node's depth in the tree.
    Parameters:
      `aNode` - the TreeNode to get the path for
      `depth` - an int giving the number of steps already taken towards the root (on recursive calls), used to size the returned array
    Returns:
      an array of TreeNodes giving the path from the root to the specified node

  - ### getUserObjectPath

    public Object[] getUserObjectPath()
    Returns the user object path, from the root, to get to this node. If some of the TreeNodes in the path have null user objects, the returned path will contain nulls.
    Returns:
      the user object path, from the root, to get to this node

  - ### getRoot

    public TreeNode getRoot()
    Returns the root of the tree that contains this node. The root is the ancestor with a null parent.
    Returns:
      the root of the tree that contains this node
    See Also:
      - `isNodeAncestor(TreeNode)`

  - ### isRoot

    public boolean isRoot()
    Returns true if this node is the root of the tree. The root is the only node in the tree with a null parent; every tree has exactly one root.
    Returns:
      true if this node is the root of its tree

  - ### getNextNode

    public DefaultMutableTreeNode getNextNode()
    Returns the node that follows this node in a preorder traversal of this node's tree. Returns null if this node is the last node of the traversal. This is an inefficient way to traverse the entire tree; use an enumeration, instead.
    Returns:
      the node that follows this node in a preorder traversal, or null if this node is last
    See Also:
      - `preorderEnumeration()`

  - ### getPreviousNode

    public DefaultMutableTreeNode getPreviousNode()
    Returns the node that precedes this node in a preorder traversal of this node's tree. Returns `null` if this node is the first node of the traversal -- the root of the tree. This is an inefficient way to traverse the entire tree; use an enumeration, instead.
    Returns:
      the node that precedes this node in a preorder traversal, or null if this node is the first
    See Also:
      - `preorderEnumeration()`

  - ### preorderEnumeration

    public Enumeration<TreeNode> preorderEnumeration()
    Creates and returns an enumeration that traverses the subtree rooted at this node in preorder. The first node returned by the enumeration's `nextElement()` method is this node.

    Modifying the tree by inserting, removing, or moving a node invalidates any enumerations created before the modification.

    Returns:
      an enumeration for traversing the tree in preorder
    See Also:
      - `postorderEnumeration()`

  - ### postorderEnumeration

    public Enumeration<TreeNode> postorderEnumeration()
    Creates and returns an enumeration that traverses the subtree rooted at this node in postorder. The first node returned by the enumeration's `nextElement()` method is the leftmost leaf. This is the same as a depth-first traversal.

    Modifying the tree by inserting, removing, or moving a node invalidates any enumerations created before the modification.

    Returns:
      an enumeration for traversing the tree in postorder
    See Also:
      - `depthFirstEnumeration()`
      - `preorderEnumeration()`

  - ### breadthFirstEnumeration

    public Enumeration<TreeNode> breadthFirstEnumeration()
    Creates and returns an enumeration that traverses the subtree rooted at this node in breadth-first order. The first node returned by the enumeration's `nextElement()` method is this node.

    Modifying the tree by inserting, removing, or moving a node invalidates any enumerations created before the modification.

    Returns:
      an enumeration for traversing the tree in breadth-first order
    See Also:
      - `depthFirstEnumeration()`

  - ### depthFirstEnumeration

    public Enumeration<TreeNode> depthFirstEnumeration()
    Creates and returns an enumeration that traverses the subtree rooted at this node in depth-first order. The first node returned by the enumeration's `nextElement()` method is the leftmost leaf. This is the same as a postorder traversal.

    Modifying the tree by inserting, removing, or moving a node invalidates any enumerations created before the modification.

    Returns:
      an enumeration for traversing the tree in depth-first order
    See Also:
      - `breadthFirstEnumeration()`
      - `postorderEnumeration()`

  - ### pathFromAncestorEnumeration

    public Enumeration<TreeNode> pathFromAncestorEnumeration(TreeNode ancestor)
    Creates and returns an enumeration that follows the path from `ancestor` to this node. The enumeration's `nextElement()` method first returns `ancestor`, then the child of `ancestor` that is an ancestor of this node, and so on, and finally returns this node. Creation of the enumeration is O(m) where m is the number of nodes between this node and `ancestor`, inclusive. Each `nextElement()` message is O(1).

    Modifying the tree by inserting, removing, or moving a node invalidates any enumerations created before the modification.

    Parameters:
      `ancestor` - the node to start enumeration from
    Returns:
      an enumeration for following the path from an ancestor of this node to this one
    Throws:
      `IllegalArgumentException` - if `ancestor` is not an ancestor of this node
    See Also:
      - `isNodeAncestor(TreeNode)`
      - `isNodeDescendant(DefaultMutableTreeNode)`

  - ### isNodeChild

    public boolean isNodeChild(TreeNode aNode)
    Returns true if `aNode` is a child of this node. If `aNode` is null, this method returns false.
    Parameters:
      `aNode` - the node to determinate whether it is a child
    Returns:
      true if `aNode` is a child of this node; false if `aNode` is null

  - ### getFirstChild

    public TreeNode getFirstChild()
    Returns this node's first child. If this node has no children, throws NoSuchElementException.
    Returns:
      the first child of this node
    Throws:
      `NoSuchElementException` - if this node has no children

  - ### getLastChild

    public TreeNode getLastChild()
    Returns this node's last child. If this node has no children, throws NoSuchElementException.
    Returns:
      the last child of this node
    Throws:
      `NoSuchElementException` - if this node has no children

  - ### getChildAfter

    public TreeNode getChildAfter(TreeNode aChild)
    Returns the child in this node's child array that immediately follows `aChild`, which must be a child of this node. If `aChild` is the last child, returns null. This method performs a linear search of this node's children for `aChild` and is O(n) where n is the number of children; to traverse the entire array of children, use an enumeration instead.
    Parameters:
      `aChild` - the child node to look for next child after it
    Returns:
      the child of this node that immediately follows `aChild`
    Throws:
      `IllegalArgumentException` - if `aChild` is null or is not a child of this node
    See Also:
      - `children`

  - ### getChildBefore

    public TreeNode getChildBefore(TreeNode aChild)
    Returns the child in this node's child array that immediately precedes `aChild`, which must be a child of this node. If `aChild` is the first child, returns null. This method performs a linear search of this node's children for `aChild` and is O(n) where n is the number of children.
    Parameters:
      `aChild` - the child node to look for previous child before it
    Returns:
      the child of this node that immediately precedes `aChild`
    Throws:
      `IllegalArgumentException` - if `aChild` is null or is not a child of this node

  - ### isNodeSibling

    public boolean isNodeSibling(TreeNode anotherNode)
    Returns true if `anotherNode` is a sibling of (has the same parent as) this node. A node is its own sibling. If `anotherNode` is null, returns false.
    Parameters:
      `anotherNode` - node to test as sibling of this node
    Returns:
      true if `anotherNode` is a sibling of this node

  - ### getSiblingCount

    public int getSiblingCount()
    Returns the number of siblings of this node. A node is its own sibling (if it has no parent or no siblings, this method returns `1`).
    Returns:
      the number of siblings of this node

  - ### getNextSibling

    public DefaultMutableTreeNode getNextSibling()
    Returns the next sibling of this node in the parent's children array. Returns null if this node has no parent or is the parent's last child. This method performs a linear search that is O(n) where n is the number of children; to traverse the entire array, use the parent's child enumeration instead.
    Returns:
      the sibling of this node that immediately follows this node
    See Also:
      - `children`

  - ### getPreviousSibling

    public DefaultMutableTreeNode getPreviousSibling()
    Returns the previous sibling of this node in the parent's children array. Returns null if this node has no parent or is the parent's first child. This method performs a linear search that is O(n) where n is the number of children.
    Returns:
      the sibling of this node that immediately precedes this node

  - ### isLeaf

    public boolean isLeaf()
    Returns true if this node has no children. To distinguish between nodes that have no children and nodes that cannot have children (e.g. to distinguish files from empty directories), use this method in conjunction with `getAllowsChildren`
    Specified by:
      `isLeaf` in interface `TreeNode`
    Returns:
      true if this node has no children
    See Also:
      - `getAllowsChildren()`

  - ### getFirstLeaf

    public DefaultMutableTreeNode getFirstLeaf()
    Finds and returns the first leaf that is a descendant of this node -- either this node or its first child's first leaf. Returns this node if it is a leaf.
    Returns:
      the first leaf in the subtree rooted at this node
    See Also:
      - `isLeaf()`
      - `isNodeDescendant(DefaultMutableTreeNode)`

  - ### getLastLeaf

    public DefaultMutableTreeNode getLastLeaf()
    Finds and returns the last leaf that is a descendant of this node -- either this node or its last child's last leaf. Returns this node if it is a leaf.
    Returns:
      the last leaf in the subtree rooted at this node
    See Also:
      - `isLeaf()`
      - `isNodeDescendant(DefaultMutableTreeNode)`

  - ### getNextLeaf

    public DefaultMutableTreeNode getNextLeaf()
    Returns the leaf after this node or null if this node is the last leaf in the tree.

    In this implementation of the `MutableNode` interface, this operation is very inefficient. In order to determine the next node, this method first performs a linear search in the parent's child-list in order to find the current node.

    That implementation makes the operation suitable for short traversals from a known position. But to traverse all of the leaves in the tree, you should use `depthFirstEnumeration` to enumerate the nodes in the tree and use `isLeaf` on each node to determine which are leaves.

    Returns:
      returns the next leaf past this node
    See Also:
      - `depthFirstEnumeration()`
      - `isLeaf()`

  - ### getPreviousLeaf

    public DefaultMutableTreeNode getPreviousLeaf()
    Returns the leaf before this node or null if this node is the first leaf in the tree.

    In this implementation of the `MutableNode` interface, this operation is very inefficient. In order to determine the previous node, this method first performs a linear search in the parent's child-list in order to find the current node.

    That implementation makes the operation suitable for short traversals from a known position. But to traverse all of the leaves in the tree, you should use `depthFirstEnumeration` to enumerate the nodes in the tree and use `isLeaf` on each node to determine which are leaves.

    Returns:
      returns the leaf before this node
    See Also:
      - `depthFirstEnumeration()`
      - `isLeaf()`

  - ### getLeafCount

    public int getLeafCount()
    Returns the total number of leaves that are descendants of this node. If this node is a leaf, returns `1`. This method is O(n) where n is the number of descendants of this node.
    Returns:
      the number of leaves beneath this node
    See Also:
      - `isNodeAncestor(TreeNode)`

  - ### toString

    public String toString()
    Returns the result of sending `toString()` to this node's user object, or the empty string if the node has no user object.
    Overrides:
      `toString` in class `Object`
    Returns:
      a string representation of the object
    See Also:
      - `getUserObject()`

  - ### clone

    public Object clone()
    Overridden to make clone public. Returns a shallow copy of this node; the new node has no parent or children and has a reference to the same user object, if any.
    Overrides:
      `clone` in class `Object`
    Returns:
      a copy of this node
    See Also:
      - `Cloneable`