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 samcu = 9;
double ra = 2.0;
int brirpres = 7;

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

1 + samcu / 5 - 6 * 5 % 6 + ra - brirpres

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 pi = 5;
int grelbian = 1;
int ed = 8;
int sa = 3;
double ciplod = 2.0;
boolean beb = true;
int chesh = 3;
int phe = 1;

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

pi > grelbian || 1 == ed && !(sa == 5) || ciplod > 0 && beb != chesh <= 3 || !(phe <= 5)

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:

• Variable scope and lifetime: Correct Solution (gfc2-hjht-zis8-6bze)
• Closures and event handling: Correct Solution (Lyad-ekd4-qjzh-2qop)