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 iups = 7;
int ia = 5;

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

3 / (iups - 8 - ia) / 5

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:

boolean rioc = true;
int hidting = 7;
int conle = 6;

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

2 != 2 && rioc && hidting >= conle && !(0 >= 7)

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:

• Closures and event handling: Correct Solution (Lweb-sork-dspc-eoob)
• Stack frames and objects (like the Idea Lab activity): Correct Solution (1d9k-546v-78o8-8qtk-w)