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 pe = 2.0;
double ceupo = 4.0;
double dios = 4.0;

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

2 - pe - (4 * ceupo % dios)

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 id = true;
int et = 7;
int unbril = 2;
int scuav = 7;
double pou = 5.0;
int hosil = 2;

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

!id || (et >= unbril || scuav >= 0) || pou > hosil

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:

• Variable scope and lifetime: Correct Solution (gfb1-55mf-uLpd-7yo7)
• Class relationships: Correct Solution (rkL9-oebr-etf2-5uqm)