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 er = 3.0;
double pror = 5.0;

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

4 - er - pror

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 sitdo = false;
boolean fle = true;

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

sitdo && fle

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"

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:

• Booleans and conditionals: Correct Solution (5Lr2-8q2q-287y-22a7)
• Stack frames and objects (like the Idea Lab activity): Correct Solution (1d8b-zdc0-fiai-esjb-g)
• Variable scope and lifetime: Correct Solution (gf0a-mzsm-9hb7-gj6w)