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 prastcross = 1;
int en = 9;
int biorde = 5;

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

prastcross * 6 + en / 8 - 3 * biorde

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 em = 5;
double basi = 2.0;
boolean mena = false;
int oima = 4;

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

em != 0 || 4 <= basi == (2 == 1) || mena != oima < 4

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

Solution

Things to double-check in your solution:

• Did you indicate the distinction between ints and Strings?
• Are your left/right branches correct?

Related puzzles:

• Closures and event handling: Correct Solution (Lzfw-tn80-31nu-71ui)
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• Variable scope and lifetime: Correct Solution (gf0u-ide2-m6ti-nyh9)