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 skucta = 3.0;
double ne = 2.0;
int lihit = 1;
double kodpo = 5.0;

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

(3 + skucta * ne / lihit - kodpo) * 7 / 8

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 worfa = 3.0;
double wucie = 5.0;
boolean ma = false;
int as = 5;
int podte = 3;
double fi = 1.0;

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

worfa >= wucie && 9 <= 8 == ma && 9 >= as && podte > 7 && 5 >= fi

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"

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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