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 fel = 1;
double pantud = 3.0;
int ecpil = 7;

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

6 % fel % pantud % 9 - 9 - 3 * ecpil

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 tre = true;
int tacsint = 5;
double nintri = 2.0;
int se = 7;
boolean iodclon = false;
boolean ri = true;
boolean posec = false;

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

tre || tacsint != nintri == 3 >= se || iodclon != !ri != posec

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)

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:

• Stack frames and objects (like the Idea Lab activity): Correct Solution (1d8h-im49-7vnz-0278-4)
• Static and runtime types: Correct Solution (wtao-5mfm-dsn2-v8zt)