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 ec = 8;
double treell = 4.0;
double se = 3.0;
int obiss = 4;
double acdo = 5.0;

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

ec - treell / 4 / (4 % se - 1 - obiss - 2 % 4) % 5 % acdo

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 o = 2.0;
int me = 9;
boolean co = true;
int diu = 5;
int codeng = 1;
int cilnal = 4;
int ma = 7;
double gahios = 2.0;
double hercid = 4.0;

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

o == 9 && 1 > me != !co || (!(1 > 4) == (1 != diu) && codeng >= cilnal || ma < gahios) || 0 < 7 != hercid > 9 || !(0 < 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" + 7 + 8 + 9 + 10 + 11

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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