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 geesttic = 8;
int e = 9;

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

2 / 4 + geesttic + e

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 ca = 1;
int wreosmsal = 1;
int ceanse = 8;
double a = 2.0;

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

ca >= 1 || wreosmsal != ceanse || 5 == a

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:

• Variable scope and lifetime: Correct Solution (gf5v-d4n8-c7za-i7d5)
• Class declarations and object modeling: Correct Solution (17u6-jgyc-qs9w-acov-q)
• Stack frames and objects (like the Idea Lab activity): Correct Solution (1db4-xayd-gmok-yp5i-u)
• While loops and for loops: Correct Solution (290b-r9r5-7js4-s9u)