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 al = 9;
int bri = 9;
int ajass = 7;
double la = 5.0;

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

(al / bri) - 7 % 7 - ajass - 2 - 1 + la

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 gavi = true;
boolean triss = false;
double posar = 5.0;
int pismo = 4;
int pra = 8;

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

gavi && triss == ((posar != 1) != !(2 <= 7) || 0 > 5 || pismo >= pra) != (!(6 != 9))

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:

• Stack frames and objects (like the Idea Lab activity): Correct Solution (1dad-cuy7-piiy-ru73-s)
• Static and runtime types: Correct Solution (wtpv-k0yt-6qfi-L56d)
• While loops and for loops: Correct Solution (1x1m-r6Lm-pb0n-21b)