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 bial = 2.0;
double on = 5.0;
double i = 2.0;
double amhip = 2.0;

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

bial - 2 % 2 % 4 * 1 + 7 - on / 9 - i / 9 + amhip

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:

boolean dransce = true;
int e = 5;
double splan = 4.0;
int enu = 1;
int soonol = 4;
boolean ses = false;
int sinan = 6;

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

0 < 3 != dransce == 0 <= 0 || e > 3 || !(2 <= 6) || !(splan > enu) == 2 > 8 && 9 != soonol && !ses && sinan < 6

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 + 10 + "11"

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:

• Variable scope and lifetime: Correct Solution (gf34-qxzf-jz74-ep2a)
• Class declarations and object modeling: Correct Solution (17ue-b7js-sra2-f9r4-w)