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 esm = 4;
int wesriaph = 5;
int fo = 5;
int pe = 8;

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

esm + 6 % 4 + 6 * 9 - 7 % (wesriaph + fo * pe)

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 pirs = false;
int incen = 1;
int hidpiot = 1;
int clua = 3;
int za = 1;
double fealpu = 2.0;
int proctroll = 2;

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

4 > 4 == pirs || 6 == incen != hidpiot > clua != (9 != za) != (6 == fealpu) || 0 <= 4 != proctroll < 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" + 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:

• Class declarations and object modeling: Correct Solution (17v3-hhf6-j2vw-s83f-6)
• Variable scope and lifetime: Correct Solution (gf0z-34a7-w794-386n)