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 soost = 9;
int folqa = 4;
int ex = 4;
int et = 1;
int caer = 9;

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

9 % soost % folqa - ex * et + caer

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 redspu = 3;
boolean ciorie = true;
boolean doshul = false;
boolean tard = false;
double ces = 3.0;
double pela = 2.0;

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

0 < redspu || (ciorie == doshul != !tard) != ces >= pela

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

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 (1daL-kf85-dufm-zrrg-n)
• While loops and for loops: Correct Solution (347u-vw19-x2y0-cbd)