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 ticrash = 5.0;
int edior = 6;
double qojem = 2.0;
double leoben = 3.0;
int derra = 6;
int jirbist = 8;
int heso = 3;

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

ticrash * edior * 6 % qojem - 8 + 4 - 7 / leoben % derra * (jirbist - 5 * heso)

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 sonen = true;
double chist = 1.0;
double fle = 3.0;
int mosfen = 9;
int riassa = 4;
boolean ec = false;
double phal = 5.0;
double mo = 3.0;

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

(sonen != 3 >= 0 != !(!(6 < 1)) && chist <= fle && mosfen <= 5 != riassa <= 0) == (5 != 6) == ec != 6 >= phal != 4 >= 5 && mo == 3

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 + 9 + 10 + 11 + 12

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:

• While loops and for loops: Correct Solution (2km2-41wn-9zf0-Lem)
• Variable scope and lifetime: Correct Solution (gf3t-38p6-346w-d1pn)
• Stack frames and objects (like the Idea Lab activity): Correct Solution (1d93-znhj-17sh-wep1-u)
• Closures and event handling: Correct Solution (Lwt4-tij3-sjdm-3ou3)
• Class relationships: Correct Solution (re5m-eup6-jgrv-i9bi)