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 prencit = 8;
double sichon = 1.0;
int droda = 1;
int laxpel = 8;
int apac = 3;
double ouwust = 1.0;
int munmi = 9;
int nesscir = 5;
int jang = 9;

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

prencit / (sichon * 1 - droda - laxpel * apac * 4 * ouwust) % munmi * nesscir % jang

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 qom = true;
boolean xensmer = false;
double pentrec = 3.0;
double briacprep = 5.0;
double flenrast = 5.0;
double anep = 4.0;
int daches = 4;

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

7 != 9 != qom != xensmer == (0 == 1) && 7 <= 8 || pentrec <= 7 && briacprep < flenrast && anep > daches && 0 >= 7 || 5 <= 5

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" + 8 + 9 + 10 + "11"

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 (1dbL-2vhh-o5wr-oate-2)
• Variable scope and lifetime: Correct Solution (gf4n-0ac0-1ws8-8fLb)