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:

double ferhec = 4.0;
int spuac = 8;
int ec = 7;
double seos = 1.0;

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

(ferhec + 4 % spuac - ec + seos)

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:

int paen = 5;
int frodor = 9;
boolean gne = false;

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

6 >= paen || (4 >= 3 || frodor >= 2) && !gne

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

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:

• Booleans and conditionals: Correct Solution (5mxb-3dLd-6ni7-8rw4)
• Class relationships: Correct Solution (rgvp-459k-6ksn-57zn)
• Closures and event handling: Correct Solution (Lvrk-4423-ndpg-rxc9)