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 ta = 2.0;
int rhat = 3;
double pio = 4.0;
int ussscass = 7;
int lapen = 6;

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

ta % 1 * rhat % 1 - pio - 7 / 6 / ussscass / 8 - lapen

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 me = 4;
boolean esbong = false;
boolean a = false;
double or = 5.0;
int ripsal = 9;
boolean scia = false;
boolean ed = false;

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

6 == 5 == !(1 <= me) && esbong == (6 != 6) != (a || or == 4 != ripsal <= 3 == scia == !ed)

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) + 10

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:

• Class declarations and object modeling: Correct Solution (17tk-Lebu-npix-to0p-m)
• Stack frames and objects (like the Idea Lab activity): Correct Solution (1d7z-5f0u-wfd6-imeL-2)