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 dapas = 7;
int fias = 2;
int ed = 7;
int nia = 9;
int eci = 1;

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

dapas + 6 + fias - ed * 5 * nia - eci

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 ouci = 4;
boolean idhu = true;
boolean ciua = false;
boolean a = true;

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

!(5 == ouci) == idhu || 4 != 4 && ciua != a || !(1 == 9)

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"

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 (1d89-ndqh-udbr-ajva-i)
• Booleans and conditionals: Correct Solution (5opk-275m-s6xi-4gme)