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 cirtelt = 1.0;
double heco = 4.0;
int pibpu = 5;
double chesspii = 2.0;

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

9 / 5 * cirtelt / heco * pibpu - chesspii

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:

int tacior = 9;
double brishist = 5.0;
double ra = 2.0;
double hirdon = 3.0;
boolean il = false;

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

tacior >= 9 || (brishist < 8 && 3 > ra == 3 < hirdon != il)

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 (1d7t-v3Ls-r7bg-00xy-9)
• Class relationships: Correct Solution (riou-nd5o-r9Lr-us03)