Drawing ASTs for expressions: Correct Solution

For each of the Java expressions below:

• Draw an AST for the expression.
• Show how the expression evaluates at each node in the tree.

Be sure that your tree accurately reflects how Java would evaluate the expression.

Part 1

Given the following variables:

int snon = 3;
double niobo = 1.0;
double qepa = 4.0;

...draw the AST and evaluation results for the following expression:

2 * snon - 7 / 7 / 1 + niobo - 7 / qepa

Solution

Things to double-check in your solution:

• Do you have the left and right branches on the correct side?
• Did you indicate the difference between ints and floating point values?

Part 2

Given the following variables:

boolean fe = false;
boolean ia = true;
boolean enval = true;
boolean primcad = false;
double arl = 1.0;
int nieflioss = 5;

...draw the AST and evaluation results for the following expression:

fe != ia == enval && primcad || 9 > 2 || 8 > 3 != arl < nieflioss

Solution

Things to double-check in your solution:

• Does your tree correctly reflect the precedence of && and ||?
• Did you correctly show short-circuiting? (That is when the right branch of && or || is never evaluated because the left branch already determines the answer.)

Part 3

Draw the AST and evaluation results for the following expression:

0 + 1 + 2 + 3 + 4 + 5 + 6 + "7" + "8"

Solution

Things to double-check in your solution:

• Did you indicate the distinction between ints and Strings?
• Are your left/right branches correct?

Related puzzles:

• Closures and event handling: Correct Solution (Lweb-sork-dspc-eoob)
• Stack frames and objects (like the Idea Lab activity): Correct Solution (1d9k-546v-78o8-8qtk-w)