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 re = 8;
double tiasec = 2.0;
int spo = 1;
int straa = 8;
int zessis = 2;
double sendcin = 3.0;

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

(re * tiasec + spo * straa) / zessis % 2 * sendcin + 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 vendci = true;
int benpri = 7;
int dipid = 3;
boolean drismkerk = false;
double enlasm = 4.0;
int fankqen = 5;
double soo = 2.0;

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

vendci == (!(benpri == dipid)) || (drismkerk || enlasm < 5 == 2 < fankqen) && soo < 1 || 2 == 4

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

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 (geuk-n44a-2qd9-5jth)
• Class relationships: Correct Solution (rf8o-2rn8-rexh-1nq7)