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:

double er = 3.0;
double samad = 2.0;
int oa = 5;
int lendiss = 6;
double va = 3.0;

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

er / (samad % oa * lendiss - va)

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 gledan = 1;
int na = 4;
int ris = 1;
double necset = 5.0;
double pregncap = 2.0;

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

3 >= gledan || 7 < na || 9 < ris && necset < pregncap

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

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 (Lzxn-tm2h-oc3u-iao3)
• Static and runtime types: Correct Solution (wtc7-pLr9-j7tx-qLLk)