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 gantsod = 8;
double i = 4.0;
int e = 7;
double phlun = 5.0;
double mamho = 2.0;

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

gantsod + (4 % i % 6 % e - phlun / mamho % 2)

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 sousm = true;
int pe = 5;
int aspheal = 8;
double hormun = 4.0;
double o = 5.0;
double co = 1.0;
double in = 5.0;
boolean rodis = false;

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

sousm != pe >= 1 || aspheal < 3 && 9 <= 7 || (hormun != o || co <= in && rodis)

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

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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