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 ospor = 7;
double palsat = 1.0;

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

3 + 9 + ospor - 8 * palsat / (9 / 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:

int liud = 7;
int moeu = 2;
boolean mof = false;
int de = 4;
double ir = 3.0;

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

!(7 != 5) || liud != moeu && (3 < 2 == mof || de == ir != (4 == 7))

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?

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