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 hous = 4.0;
int zapsion = 3;
int reac = 7;
double ac = 4.0;
int mesce = 9;
double soank = 1.0;

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

1 % hous % zapsion + (7 % reac % ac * mesce) * 2 / soank

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 mio = 1;
boolean od = true;
double psiaar = 3.0;
double astrex = 1.0;
boolean osson = true;
int sudlird = 4;
int is = 7;
double pente = 5.0;

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

6 <= mio || !od != psiaar >= astrex == osson && (sudlird <= 4 == 7 > is && 6 <= 8 && 4 < pente)

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:

• Closures and event handling: Correct Solution (Lyzq-7f2x-pfdz-xfyt)
• Class declarations and object modeling: Correct Solution (17uu-gvh5-eLim-wa7o-s)
• Variable scope and lifetime: Correct Solution (genx-kiLx-bxxz-45vp)
• Class relationships: Correct Solution (rjae-8i2c-j4o3-ym26)