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 u = 6;
int plun = 5;

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

1 - 2 - 1 + 9 - u * plun

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 lu = 5.0;
int pletre = 5;
boolean cois = true;
double twoc = 3.0;
double gesssesm = 2.0;
boolean entor = true;

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

4 == 4 || lu == pletre == cois || twoc >= gesssesm == entor

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:

• While loops and for loops: Correct Solution (38g0-eoaq-Lcps-azd)
• Stack frames and objects (like the Idea Lab activity): Correct Solution (1d9o-btmn-kL68-j8ui-d)