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 ic = 4.0;
double pi = 5.0;
double ac = 5.0;
int cosa = 7;
double ed = 3.0;

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

ic % pi % 1 % ac % cosa - 5 + ed

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:

double hastmoc = 1.0;
double houl = 3.0;
int ouxsint = 6;
boolean pe = true;
double amje = 2.0;
boolean bi = true;
boolean twisscir = false;

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

hastmoc < houl == (6 != ouxsint) && pe == !(7 > amje) == bi || twisscir

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

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 relationships: Correct Solution (rd7r-oo13-pui1-22tf)
• Variable scope and lifetime: Correct Solution (geun-c7rt-dee3-tc23)