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 iish = 3.0;
double swir = 2.0;
double unghe = 3.0;

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

5 * 6 * iish - 5 % 7 + 4 % swir / unghe % 7

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 jia = false;
boolean mossdo = true;
int ho = 6;
int pi = 6;
boolean tiblo = false;
int cirdrel = 1;
boolean domcarm = true;

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

jia != 4 <= 7 || mossdo != (9 > ho && !(9 == pi)) || tiblo != (1 != cirdrel) != domcarm

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"

Solution

Things to double-check in your solution:

• Did you indicate the distinction between ints and Strings?
• Are your left/right branches correct?

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