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 goadso = 2.0;

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

5 + 9 % goadso * 9 + 9

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 iar = true;
double rocle = 1.0;
int ki = 9;
boolean aci = false;

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

iar && 1 < rocle || (9 >= ki || aci)

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

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 (1dad-hbii-xL1k-y18g-3)
• Variable scope and lifetime: Correct Solution (gf98-yk1e-Leyx-evv4)