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 eodna = 3;
int epiass = 7;
int godmor = 4;

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

(3 * eodna + epiass / godmor) / 7 - 7

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 an = 2.0;
boolean fi = false;
int ete = 2;
int am = 5;
boolean dianval = false;

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

!(3 <= an) && fi || (ete != am && 6 != 4) || dianval

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 (1d97-gtf1-g0ma-twdb-p)
• Variable scope and lifetime: Correct Solution (gf1h-w97k-dufk-m0td)