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 ma = 9;
int brun = 2;
int chrer = 4;
double tetriss = 4.0;

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

ma + 9 + 6 % 2 + brun + chrer % 5 * tetriss + 9

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 grepad = true;
boolean bont = false;
boolean lekit = false;
int i = 9;
int meouc = 7;
double ed = 3.0;
int sqee = 6;

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

!grepad != bont == lekit && 9 >= i || 5 > meouc && 8 <= ed == !(!(9 >= 5)) == sqee < 0

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) + 9

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:

• Stack frames and objects (like the Idea Lab activity): Correct Solution (1d7v-tf7b-f6ix-730q-t)
• Booleans and conditionals: Correct Solution (5o0w-rLm3-78oe-7o5f)