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 as = 9;
double dac = 3.0;
double noss = 1.0;

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

(as * dac) + 0 - noss - 8 - 2 + 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 el = false;
double be = 5.0;
int mared = 4;
double sqad = 5.0;
int ondres = 5;
int swe = 5;

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

5 == 2 == el == 3 <= be || mared >= 3 == (4 != sqad) != (ondres == swe)

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?

Related puzzles:

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