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 palgres = 1;
int danposs = 4;
double si = 3.0;

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

palgres % danposs * si / 8

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 trepast = 7;
int iblic = 1;
boolean secaft = true;
double weano = 4.0;

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

trepast != iblic && (secaft || weano == 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"

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 (rjek-awg5-4cym-Lnvo)
• Variable scope and lifetime: Correct Solution (gepz-8ceo-ohoi-zfce)
• Static and runtime types: Correct Solution (wts5-8xzh-hkve-a6fx)