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 urt = 1.0;
int uhour = 2;
double bewnesm = 3.0;
double plio = 2.0;

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

urt + 7 * uhour % bewnesm / 3 * 6 / plio

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:

double de = 1.0;
double un = 2.0;
boolean osclab = false;
double declin = 2.0;
double bedcher = 1.0;
int es = 7;

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

7 > 9 == de < un != 7 < 7 && !osclab || declin == bedcher && 0 >= es

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"

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 (ges1-jpvr-nyne-5wcj)
• Booleans and conditionals: Correct Solution (5mnw-51hc-r5fv-ibhk)