Question
The purpose of the code is to perform the evaluation of binary expression trees (like the one below).
(+)
(*) (2)
(+) (-)
3 4 5 2
In the code snippet I have, I am confused about how if (root.getLeft() == null || root.getRight() == null) checks for missing operands. If it is a leaf node (operand), will it cause an exception (as the if condition will be true)? I also put the question as a comment in the code near the if-statement.
public float calculateValue(TreeNode root) {
// Check that the root value is not null
if (root == null) {
throw new IllegalArgumentException("Root Node must have a value");
}
// If this is a leaf node, it should be a number, so return this
if (root.getLeft() == null && root.getRight() == null) {
try {
return Float.parseFloat(root.getItem().toString());
} catch (NumberFormatException parseError) {
throw new NumberFormatException("Leaves must be numeric");
}
}
// Validate that we have operands
if (root.getLeft() == null || root.getRight() == null) {
// How does this check for missing operands? If it is a leaf node (operand),
// will it cause an exception (as the if condition will be true)?
throw new IllegalArgumentException("Operator missing operandsâ€);
}
// Retrieve the operands
float leftOperand = calculateValue(root.getLeft());
float rightOperand = calculateValue(root.getRight());
// Extract the operator
String operatorString = root.getItem().toString();
if (operatorString.length() > 1) {
throw new IllegalArgumentException("Invalid operation!");
}
char operator = operatorString.charAt(0);
// Evaluate the operation
Accepted Answer
Below I've got your code up to that if-statement with the comments removed:
if (root == null) {
throw new IllegalArgumentException("Root Node must have a value");
}
if (root.getLeft() == null && root.getRight() == null) {
try {
return Float.parseFloat(root.getItem().toString());
} catch (NumberFormatException parseError) {
throw new NumberFormatException("Leaves must be numeric");
}
}
if (root.getLeft() == null || root.getRight() == null) {
throw new IllegalArgumentException("Operator missing operands");
}
To answer your question, note that in the case of a leaf node, the second if-statement is true. Thus, it will go through that try-catch and never even execute if (root.getLeft() == null || root.getRight() == null).
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