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 isas = 5.0;
double iececk = 5.0;
double ta = 2.0;

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

isas - 7 + 8 - iececk - 9 % ta / 4 - 6

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 en = 4.0;
int enes = 2;
int vemi = 3;
double or = 4.0;
int ashbo = 7;
double kir = 3.0;
boolean e = true;
int riadcon = 7;
double chiw = 5.0;

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

7 != en == enes >= vemi && or == 0 == (ashbo < 8 != (kir == 7) && e) != riadcon > chiw

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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