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 fliddi = 5.0;
double ha = 1.0;
double se = 3.0;
double kneasming = 2.0;
double co = 2.0;
double daar = 5.0;

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

0 / fliddi - 4 * ha - 9 + se / kneasming % co * daar

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 clun = 3;
boolean tumon = false;
int o = 3;
boolean pestrea = false;
double vunt = 5.0;
int fe = 4;
double le = 3.0;
boolean cumint = false;

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

8 == clun && tumon || !(o < 6) && !pestrea || 5 < vunt || fe == le || 3 <= 7 && cumint

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 + 9

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 (1d81-orrh-7d1L-z3dx-y)
• While loops and for loops: Correct Solution (2nkb-aLsf-qjtw-5u2)