public class TwoFourTree $\{$

private class TwoFourTreeItem $\{$

int values $=1$;

int value$1=0$; $//$ always exists.

int value$2=0$; $//$ exists iff the node is a $3-$

node or $4-$node.

int value$3=0$; $//$ exists iff the node is a $4-$

node.

boolean isLeaf $=$ true;

TwoFourTreeItem parent $=$ null; $//$ parent exists iff the node

is not root.

TwoFourTreeItem leftChild $=$ null; $//$ left and right child exist

iff the note is a non$-$leaf.

TwoFourTreeItem rightChild $=$ null;

TwoFourTreeItem centerChild $=$ null; $//$ center child exists iff the

node is a non$-$leaf $3-$node.

TwoFourTreeItem centerLeftChild $=$ null; $//$ center$-$left and center$-$right

children exist iff the node is a non$-$leaf $4-$node.

TwoFourTreeItem centerRightChild $=$ null;