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 oistthi = 2;
int icai = 9;
int ro = 2;

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

oistthi / 5 + 4 - icai % 7 + ro / 7

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:

double oinind = 1.0;
int ulpoi = 3;
double cle = 2.0;
double attis = 2.0;
boolean me = false;
int teau = 2;
boolean beness = false;

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

oinind == ulpoi != 4 >= 7 != (!(cle == attis)) != me || !(teau != 9) && beness

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"

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 declarations and object modeling: Correct Solution (17uk-1055-1f60-y0mf-w)
• Stack frames and objects (like the Idea Lab activity): Correct Solution (1d98-4gcs-31pL-692z-3)