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 pid = 5.0;
int dormne = 5;
int gartuf = 4;

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

pid / 7 + 8 - (dormne / gartuf)

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 fistask = 3;
double en = 5.0;
boolean pha = false;
boolean hil = true;
double gengo = 1.0;

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

fistask == en && pha && hil && gengo != 6

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"

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:

• Booleans and conditionals: Correct Solution (5ixw-h6c2-efnq-oprv)
• Closures and event handling: Correct Solution (Lweb-sork-dspc-eoob)