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 ispear = 5.0;
int as = 2;

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

ispear * 3 / as - 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:

int e = 1;
int remphvab = 4;

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

6 <= 4 || (9 <= 7 && e != remphvab)

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

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 (1d8j-bv3j-axgo-9u6w-h)
• Class declarations and object modeling: Correct Solution (17vu-5L0k-ux3e-4j4r-L)