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 wisso = 1.0;
int esta = 8;
double i = 1.0;

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

(7 + 2 + 2 / wisso / 9 + 6 + esta - 6 + i)

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 weaxnion = 8;
int irsha = 7;
boolean desp = true;
double o = 3.0;
int mocewl = 2;
double poin = 5.0;
boolean neclerk = true;

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

weaxnion > 6 && 7 != irsha && 4 < 0 == (!(5 == 4)) != desp || o >= mocewl != 9 > poin || neclerk

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 + 9

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:

• While loops and for loops: Correct Solution (12n2-v20x-xhuf-fye)
• Closures and event handling: Correct Solution (Lwjo-equo-dage-pgcg)
• Stack frames and objects (like the Idea Lab activity): Correct Solution (1da5-28uz-ip1e-h90r-i)