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 se = 8;
double pedesm = 4.0;
double pla = 4.0;

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

5 + 6 - se * pedesm + 8 % pla

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 so = 1.0;
int or = 1;
boolean e = true;
int graxa = 2;

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

so != or != (e == 8 <= graxa != 0 < 8) && 8 <= 5

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)

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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