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 ein = 4;
int steder = 9;
int craen = 5;

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

(8 - ein) * steder - 3 * craen

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 stotol = 5.0;
boolean fe = true;
boolean ond = false;
double ronnrel = 2.0;

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

(stotol > 3 && fe) && ond && ronnrel <= 8

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:

• Booleans and conditionals: Correct Solution (5id7-av51-r5b2-pc77)
• Class declarations and object modeling: Correct Solution (17sc-dg1x-39pz-sgcw-5)