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 ilsack = 8;
double phe = 5.0;
int e = 5;
double sisiar = 2.0;
double bisosm = 5.0;

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

ilsack * phe * e - sisiar + bisosm

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 paeo = true;
boolean itrir = false;
boolean miphah = true;

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

paeo || (!(1 <= 7) || itrir && miphah)

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 (1dbb-rwdt-rm94-rdtt-n)
• Closures and event handling: Correct Solution (Lwc2-ajnt-xo99-tnc7)