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 bestheld = 4.0;
int eahe = 8;
double cangsa = 3.0;
double nirk = 5.0;
int sa = 6;
double cinpin = 3.0;

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

bestheld - eahe + cangsa + 6 / 5 % nirk + sa / cinpin

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 co = 4.0;
boolean vit = false;
double ofe = 2.0;
double a = 4.0;
int hesshass = 1;
int witcob = 2;
int rocro = 8;

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

4 <= 0 == !(2 >= 2) || 5 >= co == vit && ofe != a == hesshass > 0 && witcob >= rocro

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?

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