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 doin = 5.0;
double jistat = 3.0;
double nasienx = 4.0;

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

2 / 8 - (doin / jistat * nasienx + 8)

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:

int daunu = 4;
int pri = 2;
double strotrack = 5.0;
double plalac = 1.0;
double plir = 1.0;
double il = 5.0;

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

daunu > pri == 9 < strotrack == (plalac != plir) || !(il < 4) && 6 == 6

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

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 (1dbh-ra5L-ctxf-afs0-t)
• Closures and event handling: Correct Solution (Lviy-L461-r848-f5e5)