1. Comparing Python and Java
CS102
Dean Zeller and Robert Carver
Spring 2018

2. Hello World – Python & Java
print() prints the supplied content to the user via console output.
Console output to the user:

3. Data types & Variables Python Java Variables need no declaration.
Variables can change type at any time.
All variables must be declared in order to be used.
Data type cannot change once declared.

4. Java Data types
Reminder: all variables must be defined once and only once.
Type Name
Kind of Value
Memory Used
Range of Values
byte
Integer
1 byte
-128 to 127
short
2 bytes
-32,768 to 32,768
int
4 bytes
-2,147,483,648 to 2,147,483,648
long
8 bytes
-9,223,372,036,854,775,808 to
9,223,372,036,854,775,808
float
Floating-point
± × to ± × 10 −45
double
± × to ± × 10 −324
char
Single Unicode character
All Unicode values from 0 to 65,535
boolean
1 or more bytes
True or False

5. Java Data Types
Data Types example:

6. Array/List indices start at 0
Arrays
Python
Java
Uses Lists
Define an empty list
Add elements using append
Variable length
Uses arrays
Arrays must be defined
Add elements more complex
Length must be specified
Array/List indices start at 0
Python Example:
Output:

7. Arrays Java - Example
Assigns the array slot at the provided index to the given value.
Output:

8. Mathematical Expressions
Most operators are the same between Java and Python.
Operation
Python
Java
Usage
Example
Addition +
a+b
Same
Subtraction -
a-b
Multiplication *
a*b
Division /
a/b
Power **
a**b
Math.pow(a,b)
Parenthesis ()
3*(a+b)
Assignment =
c=a+b

9. Statement Blocks & Indentation
Python
Java
Uses curly braces {} to denote blocks of code.
All lines are ended using semi-colons (;).
Uses indentation to denote blocks of code.
Blocks start with a colon on the defining line.
Python example:
Denotes start of block
Code Blocks

10. Java Example Blocks are set off by lines without semicolon
Code blocks are enclosed with {}
Blocks are set off by lines without semicolon
Lines end with a semicolor

11. Loops – While Executes as long as the While condition is met.
Python
Java
Output:

12. Do-While Loop
Similar to a while loop, but the loop is always executed at least once.
No Python counterpart.
Do Loop Form
do {
body-statements;
} while (test);
While Loop Form
while (test){ }

13. For Loop – Basic Form
Python
Java
Output:

14. For Loop – Java for(int i = 0; i < 10; i++) { }
Increment: Statement executed every time the loop executes.
Initialization: Done once, at beginning.
Condition: Boolean condition to continue execution of loop.

15. For Loop – Other Forms Python Java Start, End Start, End, Increment
Output:
Loop 1
Loop 2
Loop 3 1 2 3 4 5 5 6 7 8 9 10 20 30 40 50 60 70 80 90

16. For and While Loop Comparison
(initialization)
while(condition) {
(statements)
(increment) }
for((initialization),(condition),(increment)) {
(statements) }

17. For each loop Python Java
Both Python and Java provide a form of the for-loop in which the only parameter is a list. The loop then executes for each item in the list, using the for-loop variable.
Python
Java
Output:
Hello Joe
Hello Bob
Hello Kathy
Output:
Hello Joe
Hello Bob
Hello Kathy

18. Credits Script outline and final editing by Dean Zeller
Content and visual organization by Robert Carver
Reference: Java An Introduction to Problem Solving, (8th edition) by Walter Savitch