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 ebert = 3.0;
double kock = 2.0;
double pral = 5.0;

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

4 * 4 / ebert / kock / pral

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 de = 2.0;
double e = 3.0;
boolean wra = true;
boolean os = false;
boolean sospoor = false;

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

(de <= e || wra || os) || sospoor

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 (1d8n-q3ch-2fk4-0r93-i)
• Variable scope and lifetime: Correct Solution (gexs-reu2-2d7u-gojj)
• Class relationships: Correct Solution (rfxb-ycvm-cgg4-qyw9)