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 inti = 7;
double diswad = 1.0;

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

5 - 0 - inti - 3 + 7 / 8 / diswad % 1

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 tobolt = 5.0;
double wecmun = 2.0;
boolean conont = false;
boolean iss = false;
double krep = 5.0;
double sucdost = 3.0;
double roboc = 3.0;

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

4 > 7 != tobolt > wecmun && !conont != iss && 0 >= 1 || krep != 8 && sucdost <= roboc

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?

Related puzzles:

• Static and runtime types: Correct Solution (wtcb-zw3i-jgxk-h8ih)
• Booleans and conditionals: Correct Solution (5kqo-g0z6-gns9-q3kf)