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 oe = 6;
int penfont = 7;

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

oe - 6 - (2 + penfont * 2)

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 pespru = 7;
boolean clepiac = true;
boolean eii = true;
double to = 3.0;
int nonlar = 7;

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

pespru != 2 && clepiac && eii && to < nonlar

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

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 (geuv-vu3d-jiah-vibi)
• Closures and event handling: Correct Solution (Lxui-qc9u-jikp-tnLy)
• Static and runtime types: Correct Solution (wtkb-acgc-xbka-2ko3)
• Class declarations and object modeling: Correct Solution (17rs-9nnr-c4dp-vp02-e)
• Booleans and conditionals: Correct Solution (5j9t-wwj4-djs4-rf40)
• Booleans and conditionals: Correct Solution (5or9-amiy-vqw8-defa)
• Static and runtime types: Correct Solution (wtvm-5teb-nLo8-wd33)
• Static and runtime types: Correct Solution (wtf4-i2fm-v96o-v0us)