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 dimid = 6;
int hac = 9;
double othant = 4.0;

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

8 / 5 - 5 - dimid % 3 % 9 + hac % othant

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 ke = 2.0;
int no = 9;
boolean fleli = true;
boolean puost = false;
boolean unterm = true;
int ma = 2;
double emoc = 3.0;

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

ke == no == !fleli == puost && !unterm == ma >= 3 && emoc <= 2 == 5 < 9

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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