/**
* Create a jump table for a SELECT node.
*
* @param node the SELECT node.
* @return the jump table.
*/
private HashMap<Object, ICodeNode> createJumpTable(ICodeNode node) {
HashMap<Object, ICodeNode> jumpTable = new HashMap<Object, ICodeNode>();
// Loop over children that are SELECT_BRANCH nodes.
ArrayList<ICodeNode> selectChildren = node.getChildren();
for (int i = 1; i < selectChildren.size(); ++i) {
ICodeNode branchNode = selectChildren.get(i);
ICodeNode constantsNode = branchNode.getChildren().get(0);
ICodeNode statementNode = branchNode.getChildren().get(1);
// Loop over the constants children of the branch's CONSTANTS_NODE.
ArrayList<ICodeNode> constantsList = constantsNode.getChildren();
for (ICodeNode constantNode : constantsList) {
// Create a jump table entry.
// Convert a single-character string constant to a character.
Object value = constantNode.getAttribute(VALUE);
if (constantNode.getType() == STRING_CONSTANT) {
value = ((String) value).charAt(0);
}
jumpTable.put(value, statementNode);
}
}
return jumpTable;
}
/**
* Execute SELECT statement.
*
* @param node the root node of the statement.
* @return null.
*/
public Object execute(ICodeNode node) {
// Is there already an entry for this SELECT node in the
// jump table cache? If not, create a jump table entry.
HashMap<Object, ICodeNode> jumpTable = jumpCache.get(node);
if (jumpTable == null) {
jumpTable = createJumpTable(node);
jumpCache.put(node, jumpTable);
}
// Get the SELECT node's children.
ArrayList<ICodeNode> selectChildren = node.getChildren();
ICodeNode exprNode = selectChildren.get(0);
// Evaluate the SELECT expression.
ExpressionExecutor expressionExecutor = new ExpressionExecutor(this);
Object selectValue = expressionExecutor.execute(exprNode);
// If there is a selection, execute the SELECT_BRANCH's statement.
ICodeNode statementNode = jumpTable.get(selectValue);
if (statementNode != null) {
StatementExecutor statementExecutor = new StatementExecutor(this);
statementExecutor.execute(statementNode);
}
++executionCount; // count the SELECT statement itself
return null;
}