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 phionpus = 1;
int li = 2;
int il = 1;
int beph = 7;
double ia = 1.0;

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

6 * 4 * 2 - 3 - phionpus * li % il - beph % ia

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 xin = 3.0;
boolean gomed = false;
double jes = 1.0;
double ma = 4.0;
boolean iass = true;
boolean har = false;
boolean cegos = false;

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

4 >= xin && gomed || jes != 4 != (2 == ma) == 6 >= 2 || iass && har || cegos

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?

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