com.google.common.collect

Class TreeTraverser<T>

java.lang.Object

com.google.common.collect.TreeTraverser<T>

Direct Known Subclasses:

BinaryTreeTraverser

@Beta
 @GwtCompatible
public abstract class TreeTraverser<T>
extends Object

Views elements of a type T as nodes in a tree, and provides methods to traverse the trees induced by this traverser.

For example, the tree

        h
      / | \
     /  e  \
    d       g
   /|\      |
  / | \     f
 a  b  c
 

can be iterated over in preorder (hdabcegf), postorder (abcdefgh), or breadth-first order (hdegabcf).

Null nodes are strictly forbidden.

For Java 8 users: Because this is an abstract class, not an interface, you can't use a lambda expression to extend it:

 // won't work
 TreeTraverser<NodeType> traverser = node -> node.getChildNodes();
 

Instead, you can pass a lambda expression to the using factory method:

 TreeTraverser<NodeType> traverser = TreeTraverser.using(node -> node.getChildNodes());
 

Since:

15.0

Author:

Louis Wasserman

Constructor Summary

Constructors

Constructor and Description
TreeTraverser()

Method Summary

Modifier and Type	Method and Description
FluentIterable<T>	breadthFirstTraversal(T root) Returns an unmodifiable iterable over the nodes in a tree structure, using breadth-first traversal.
abstract Iterable<T>	children(T root) Returns the children of the specified node.
FluentIterable<T>	postOrderTraversal(T root) Returns an unmodifiable iterable over the nodes in a tree structure, using post-order traversal.
FluentIterable<T>	preOrderTraversal(T root) Returns an unmodifiable iterable over the nodes in a tree structure, using pre-order traversal.
static <T> TreeTraverser<T>	using(Function<T,? extends Iterable<T>> nodeToChildrenFunction) Returns a tree traverser that uses the given function to navigate from a node to its children.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TreeTraverser

public TreeTraverser()

Method Detail

using

public static <T> TreeTraverser<T> using(Function<T,? extends Iterable<T>> nodeToChildrenFunction)

Returns a tree traverser that uses the given function to navigate from a node to its children. This is useful if the function instance already exists, or so that you can supply a lambda expressions. If those circumstances don't apply, you probably don't need to use this; subclass TreeTraverser and implement its children(T) method directly.

Since:

20.0

children

public abstract Iterable<T> children(T root)

Returns the children of the specified node. Must not contain null.

preOrderTraversal

public final FluentIterable<T> preOrderTraversal(T root)

Returns an unmodifiable iterable over the nodes in a tree structure, using pre-order traversal. That is, each node's subtrees are traversed after the node itself is returned.

No guarantees are made about the behavior of the traversal when nodes change while iteration is in progress or when the iterators generated by children(T) are advanced.

postOrderTraversal

public final FluentIterable<T> postOrderTraversal(T root)

Returns an unmodifiable iterable over the nodes in a tree structure, using post-order traversal. That is, each node's subtrees are traversed before the node itself is returned.

No guarantees are made about the behavior of the traversal when nodes change while iteration is in progress or when the iterators generated by children(T) are advanced.

breadthFirstTraversal

public final FluentIterable<T> breadthFirstTraversal(T root)

Returns an unmodifiable iterable over the nodes in a tree structure, using breadth-first traversal. That is, all the nodes of depth 0 are returned, then depth 1, then 2, and so on.

No guarantees are made about the behavior of the traversal when nodes change while iteration is in progress or when the iterators generated by children(T) are advanced.