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 tism = 7;
double a = 3.0;
int edel = 7;
double ma = 1.0;
double bu = 2.0;
int rasu = 1;

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

tism - 2 * (a - edel % ma * bu % 5) * rasu

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 prefrep = false;
int precress = 8;
double knahed = 2.0;
double chua = 5.0;
double cestgearm = 4.0;
int prosuff = 8;
int i = 7;

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

prefrep && precress < 2 && knahed >= chua == 4 > 8 == (5 != 1) || cestgearm < prosuff || 4 <= i

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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