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 trudid = 5.0;
double esho = 4.0;
double menple = 4.0;
int en = 9;

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

5 * 5 * trudid - esho + 2 * menple + en - 6

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 qunbar = false;
int se = 2;
double etging = 1.0;
int alcard = 9;
int sceo = 5;
int trul = 8;
double hica = 1.0;

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

(qunbar || se != etging != alcard >= 5) != (sceo != 5) && 3 < 7 == !(4 > trul) != 7 < hica

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:

• Class relationships: Correct Solution (regk-y1nf-041c-jmsf)
• While loops and for loops: Correct Solution (3k4r-4a9e-L4hr-sbg)
• Variable scope and lifetime: Correct Solution (gf21-dfb2-ypr0-Lbkh)