So can a computer
That includes syntax for describing arithmetic expressions
I will take advantage of your knowledge in arithmetic expressions from your elementary school education.

All of the floating point (arithmetic) operators should look familiar to you...
Operator symbol  Operation  Note 

+  addition  Binary operator, e.g.: 4.0 + 5.0 = 9.0 
−  subtraction  Binary operator, e.g.: 4.0 − 5.0 = −1.0 
*  multiplication  Binary operator, e.g.: 4.0 * 5.0 = 20.0 
/  division  Binary operator, e.g.: 4.0 / 5.0 = 0.8 
( ... )  brackets  Changes order of computation 
−  negation 
Changes the sign of the value:
− 4.0 = (−4.0)
(Read as: − 4.0 = negative 4.0) 
Result of the integer operation 5.0 + 3.0 is 8.0 Result of the integer operation 5.0  3.0 is 2.0 Result of the integer operation 5.0 * 3.0 is 15.0 Result of the integer operation 5.0 / 3.0 is 1.666666666666... Use of brackets changes the order of the operations 

public class AreaOfCircle { public static void main(String[] args) { double r; // variable containing the radius double area; // variable containing the area r = 4; // Give the radius area = 3.1415 * r * r; // Compute the area of the circle System.out.print("The radius = "); System.out.println(r); System.out.print("The area = "); System.out.println(area); } } 
Notes:

Operator  Priority  Note 

( .... )  Highest  
− (negation)  Higher  Unary operator, e.g.: −3.0 
* /  High  Binary operator, e.g.: 4.0 * 5.0 
+ −  Lowest  Binary operator, e.g.: 4.0 + 5.0 

Floating point expression: 22.0  3.0 * 4.0 Evaluated as follows: 22.0  3.0 * 4.0 = 22.0  12.0 = 10.0 
Floating point expression: (22.0  3.0) * 4.0 Evaluated as follows: (22.0  3.0) * 4.0 = 19.0 * 4.0 = 76.0 
Floating point expression: 22.0   3.0 * 4.0 Evaluated as follows: 22.0   3.0 * 4.0 = 22.0  (3.0) * 4.0 = 22.0  (12.0) = 34.0 
How to run the program:

public class Average { public static void main(String[] args) { double a, b, c, avg; // Define 4 variables a = 3.0; b = 4.0; c = 6.0; avg = (a + b + c)/3.0; System.out.print("The average = "); System.out.println(avg); } } 
How to run the program:


Example of leftassociative operators:

Example:
Floating point expression: 7.0  2.0  1.0 Evaluated as follows: 7.0  2.0  1.0 (group from left to right) 5.0  1.0 4.0 

Example of rightassociative operators:

Example:
Floating point expression:     1.0 Evaluated as follows:     1.0 =    (1.0) (Note: (1.0) denotes negative 1.0 =   (1.0) =  (1.0) = 1.0 
How to run the program:


Floating point expression: 7.0 / 2.0  6.0 * 2.0 / 4.0  4.0 / 2.0 / 2.0 Evaluated as follows: 1. Make groups containing only operators of the highest priority (7.0 / 2.0)  (6.0 * 2.0 / 4.0)  (4.0 / 2.0 / 2.0) 2. Within each group, apply the operator associativity rule: (7.0 / 2.0)  (6.0 * 2.0 / 4.0)  (4.0 / 2.0 / 2.0) = (3.5)  (12.0 / 4.0)  (2.0 / 2.0) = (3.5)  (3.0)  (1.0) = 3.5  3.0  1.0 Repeat: 1. Make groups containing only operators of the highest priority (3.5  3.0  1.0) (only one group !) 2. Within each group, apply the operator associativity rule: (3.5  3.0  1.0) = (0.5  1.0) = 0.5 