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 melsess = 3.0;
int pri = 3;
double pi = 2.0;

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

(melsess / 5 * pri % pi)

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 salson = true;
boolean pting = true;

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

salson && (pting || 7 >= 8)

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

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 (1d8L-qco9-pwfu-g904-m)
• Class declarations and object modeling: Correct Solution (17so-wbbL-upoy-9u6f-i)