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 posso = 5.0;
int scou = 6;
int nend = 9;
double vero = 4.0;
double secun = 5.0;

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

posso + scou / 7 * nend - vero * secun

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 iplad = true;
boolean ue = false;
int iodpleng = 4;
double padglo = 4.0;

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

!(6 < 0) == iplad != ue == (7 != iodpleng) && padglo != 7

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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