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 fips = 2.0;
double sange = 3.0;
double punhor = 5.0;
double i = 4.0;
double resm = 3.0;
double eo = 1.0;

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

1 + fips - sange - 6 + 6 * punhor + i - resm - eo + 3 / 6

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 pisca = false;
double suad = 4.0;
double daprus = 4.0;
int el = 2;
double prer = 2.0;
double qel = 1.0;
int il = 5;
int so = 9;
int en = 6;

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

!pisca != !(3 >= 7) == suad > daprus || !(0 != el) == (7 != 3) != (6 != 8) && prer < qel || 5 <= 4 && il == 1 && so == en

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 (gevx-w77t-2rcz-09ti)
• Class relationships: Correct Solution (rf3g-s9gh-yrbh-e996)