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 iambust = 3.0;

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

6 + (0 - 7 * iambust + 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:

double paduc = 4.0;
int an = 6;
double cliedfi = 4.0;

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

9 == paduc && an >= 2 || cliedfi < 2 && 9 < 1

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:

• While loops and for loops: Correct Solution (2jr7-et3s-jtu2-4wo)
• Stack frames and objects (like the Idea Lab activity): Correct Solution (1daz-e2yt-76fk-y1nj-p)