CollectionUtilities.md

#Magni collection utility APIs

Collection utilities

Magni collection utilities provide features I miss from other collection libraries. Some of them are are relatively simple but would have been very helpful in my past work.

"Sealable" collections

org.magni.collect.sealable.SealableCollections provides static methods for creating collection wrappers that can be made read-only ("sealed") by in invoking seal() method on them. The collections are editable until sealed, after which they behave exactly like the collections returned by java.util.Collections.unmodifiable*() methods:

org.magni.collect.sealable.SealableCollections.sealableCollection(Collection<E>)
org.magni.collect.sealable.SealableCollections.sealableList(List<E>)
org.magni.collect.sealable.SealableCollections.sealableMap(Map<K, V>)
org.magni.collect.sealable.SealableCollections.sealableSet(Set<E>)
org.magni.collect.sealable.SealableCollections.sealableSortedMap(SortedMap<K, V>)
org.magni.collect.sealable.SealableCollections.sealableSortedSet(SortedSet<E>)

Tree traversal

org.magni.collect.tree.TreeTraverser allows iterating over the nodes of a tree. All you have to do is subclassing it and implementing the getChildrenOf(E parent) method properly:

new TreeTraverser<FooBarTreeNode>() {
	@Override
	protected Iterable<FooBarTreeNode> getChildrenOf(FooBarTreeNode parent) {
		
		return parent.getChildren();
	}
};

Full example for tree traversal

public class BreadthFirstTreeTraverserExample {

	/**
	 * Demonstration of what needs to be implemented 
	 * to be able to traverse a custom tree class
	 */
	private static final TreeTraverser<TestTreeNode> TESTTREENODE_TRAVERSER = 
			new TreeTraverser<TestTreeNode>() {

		@Override
		protected Iterable<TestTreeNode> getChildrenOf(TestTreeNode parent) {
			return parent.getChildren();
		}
	};
	
	
	/**
	 * Test Tree Node class for the sake of the example
	 */
	static class TestTreeNode {

		private final List<TestTreeNode> children;
		private final String name;

		TestTreeNode(String name) {
			this(name, new TestTreeNode[0]);
		}

		TestTreeNode(String name, TestTreeNode... children) {
			this.name = name;
			this.children = Arrays.asList(children);
		}

		public Iterable<TestTreeNode> getChildren() {
			return children;
		}

		/*
		 * (non-Javadoc)
		 * 
		 * @see java.lang.Object#toString()
		 */
		@Override
		public String toString() {
			return name;
		}

	}

	/**
	 * Test traversal logic on the following tree:
	 * 
	 * <tt><pre>
	 * 
	 *         a
	 *       /   \
	 *      /     \
	 *     b       c
	 *   /  \     / \
	 *  d    e   f   g
	 *  </pre></tt>
	 */
	public static void main(String[] args) {

		TestTreeNode d = new TestTreeNode("d");
		TestTreeNode e = new TestTreeNode("e");

		TestTreeNode f = new TestTreeNode("f");
		TestTreeNode g = new TestTreeNode("g");

		TestTreeNode b = new TestTreeNode("b", d, e);
		TestTreeNode c = new TestTreeNode("c", f, g);

		TestTreeNode a = new TestTreeNode("a", b, c);

		for (TestTreeNode node : TESTTREENODE_TRAVERSER.breadthFirst(a)) {

			System.out.println(node);
		}
	}
}