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 sest = 4;

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

8 * 0 % 2 - (2 - 6) - 9 * 0 + sest

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 hetross = 3.0;
boolean dac = false;
int tritoe = 2;
int cac = 7;
int in = 8;
int demp = 3;
int e = 6;
int ce = 9;
int prea = 4;

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

6 >= hetross && dac || tritoe < cac && in < 5 != 4 >= demp == !(7 > e) && ce <= prea

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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