TreeNode
class.
TreeNode(Object value)
-- Create a new tree.
void setChild(int childnum, TreeNode child)
--
Set a child (subtree) of the current tree.
TreeNode getChild(int childnum)
-- Get one of the subtrees
of the current tree.
Object value()
-- Get the value at the root of the tree.
+
in 2+3*5
.
2+3*5
has
+
at the root,
2
as the left subtree,
*
as the root of the right subtree,
3
as the left subtree of the right subtree,
and
5
as the right subtree of the right subtree.
+ / \ 2 * / \ 3 5
ExpressionTree two = new ExpressionTree(2); ExpressionTree three = new ExpressionTree(3); ExpressionTree five = new ExpressionTree(5); ExpressionTree right = new ExpressionTree(Operation.MULTIPLY, three, five); ExpressionTree whole = new ExpressionTree(Operation.ADD, two, right);
ExpressionTree whole = new ExpressionTree(); whole.setRoot(Operation.ADD); whole.setChild(0, two); whole.setChild(1, right);
/** Get the evaluate of the current expression. */ public int evaluate() throws Exception { if (type == INTEGER) { return ((Integer) getRoot()).intValue(); } // INTEGER else if (type == VARIABLE) { return lookupVariable(getRoot()); } // VARIABLE else if (type == OPERATION) { // Evaluate arguments int[] args = new int(arity()); for (int i = 0; i < arity(); ++i) { args[i] = getChild(i).evaluate(); } // for // Apply the operation return ((Operation) getRoot()).apply(args); } // OPERATION else { throw new Exception("Invalid expression tree"); } } // evaluate()
Operation
class which supports an apply(int[])
method. That method
might look something like:
public int apply(int[] args) throws MathException { if (op == ADD) { if (args.length != 2) { throw new MathException("Add requires two arguments"); } return args[0] + args[1]; } else if (op == MULTIPLY) { if (args.length != 2) { throw new MathException("Multiply requires two arguments"); } return args[0] * args[1]; } else if (op == NEGATE) { if (args.length != 1) { throw new MathException("Negation requires one argument"); } return -args[0]; } ... } // apply
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Source text last modified Wed Nov 12 12:18:48 1997.
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