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 gua = 6;
int prir = 8;
int clercoun = 9;
int onporch = 3;
int di = 7;
double snest = 5.0;

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

(gua - prir / 5 / clercoun % onporch % di) * snest / 0

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 a = 2.0;
int rhunscec = 7;
double oac = 3.0;
double haswi = 2.0;
boolean inhall = false;

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

1 == a && (!(rhunscec != oac) == 3 <= 5 || !(8 < 4) || 3 != haswi || 4 != 7) == inhall

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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