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 muckro = 8;
int prentel = 1;
int vabu = 8;
double cidsci = 2.0;

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

muckro + (prentel + vabu % 6) % 6 * cidsci

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 rhilen = 9;
int ir = 9;
double polpen = 2.0;
int psishspud = 6;

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

rhilen < ir || polpen == psishspud == (4 < 6 || !(7 > 2)) == (1 == 8)

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:

• While loops and for loops: Correct Solution (1o0e-s445-7vgg-qzo)
• Stack frames and objects (like the Idea Lab activity): Correct Solution (1d8j-oyq1-i3mr-rq7d-9)