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 puisci = 5.0;
double ea = 5.0;
int buta = 6;
double snussglang = 5.0;
int lolgli = 6;

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

puisci * 0 % ea + buta * 8 % snussglang * lolgli - 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:

double agi = 5.0;
int suda = 2;
int appu = 2;
boolean phepsi = false;
int le = 7;
double glust = 4.0;

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

9 < 4 == agi <= 3 != 8 > suda || 5 > appu || phepsi && 2 != 7 || le > glust

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:

• Stack frames and objects (like the Idea Lab activity): Correct Solution (1d89-zyLo-f7xw-6nx1-v)
• Booleans and conditionals: Correct Solution (5L60-yqot-0i2s-87wk)
• Class relationships: Correct Solution (remu-t0cx-9aqg-icz3)