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 thur = 4;
int co = 4;
int cint = 2;
int abreur = 3;

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

9 + thur * co * 8 * cint - 6 - 3 + abreur

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 cio = 2;
double kei = 3.0;
int gucjo = 2;
boolean thiopor = false;
double eossi = 2.0;
int de = 1;

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

!(3 != 3) && cio < 9 && !(5 != 6) != kei <= gucjo && thiopor && (eossi <= de == (0 == 3))

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"

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:

• Closures and event handling: Correct Solution (Lw31-oL3m-cad4-mzhv)
• Booleans and conditionals: Correct Solution (5oLa-s28y-1fmu-jp78)