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 el = 4.0;
int fre = 1;
double bekhua = 5.0;
double a = 5.0;

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

el - 4 * fre % bekhua * 7 - a

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 em = false;
int fenpa = 8;
double mutir = 3.0;
int pri = 9;
boolean fanban = true;

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

em != fenpa <= mutir == pri > 5 != (7 == 2) && fanban

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

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 (1daL-kf85-dufm-zrrg-n)
• While loops and for loops: Correct Solution (3oqx-hujj-waL6-r2h)
• Booleans and conditionals: Correct Solution (5nn2-j0db-9x75-bbu2)