FSD +003

Terminology

• Software: A set of statements written in a programming language to perform tasks
• Statement: A single instruction in a program that performs an action when executed.
• Snippet: A block of statements.
• Software Development: The process of creating a software program.
• OOP: Program composed of interconnected objects at runtime.
• Expression: An entity-code component of a statement that can be evaluated to produce a value.
• Assign: The process of storing the result (a value) of one or more expressions.
• Value: A data item (literal or computed) that is stored in a variable.
• Compiler: A special program that translates a programming language's source code into machine code.
  • Compilers complete the conversion process all at once after changes are made to the code and before the code is executed
• Interpreter: A computer program that directly executes code without requiring it to be previously compiled into machine language.
  • Interpreters complete the conversion process one step at a time while the code is being executed.

Software development

• Software development process is an iterative approach.

• java
  • javac Welcome.java: Compiles the Java source file Welcome.java into class binary file.
  • java Welcome: Executes the Java program Welcome.
• python
  • python welcome.py: Executes the Python script welcome.py.

OOP

• Object: An object is a thing, tangible and intangible. An object has fields that contain the data and methods to access and modify the data.
• Class: A class is an abstract definition of objects. A class is a template of a blueprint that defines what data and methods are included in objects.
• Method: A block of code grouped together to perform an operation. A method has a name, parameters, and a return type.
• Field: A field is a data attribute of an object. A field value is exposed using object methods.
• Organizing code into classes improves modularity, reusability, extendability, and scalability.

Java vs Python

Identifier type	Java	Python
Class	Use CamelCase for multi-word classes	Use snake_case for multi-word classes
Function	use verbs or verb phrases	use lowercase_with_underscores
Procedure	use verbs or verb phrases	use lowercase_with_underscores
Variable	camelCase	lowercase_with_underscores
Constant	All uppercase words separated by underscores	All uppercase words separated by underscores
Package	Lowercase words separated by dots	Lowercase words separated by underscores

• Java uses the toString() function to return objects' information.
• Python can refer to attributes directly or use the __str()__ function to return objects' information

Data types

Data Type	Size	Default value	Description
byte	1 byte	0	8-bit signed integer
short	2 bytes	0	16-bit signed integer
int	4 bytes	0	32-bit signed integer
long	8 bytes	0	64-bit signed integer
float	4 bytes	0.0f	32-bit floating point
double	8 bytes	0.0d	64-bit floating point
boolean	1 bit	false	true or false
char	2 bytes	'\u0000'	16-bit Unicode character

Non-Primitive Data Types

• Non-primitive: Arrays, Classes, Interfaces, and Strings.
• Non-primitive data types are by default set to null in Java, None in Python.

Variables

• Static: enables the variable to be used without creating an object of its defining class.
• Final: makes the variable unchangeable.

Operators

Operator Category	Java	Python
Unary	expr++ expr--
	++expr --expr +expr -expr	+expr -expr
Arithmetic	* / &	* / &
	+ -	+ -
Relational	< > <= >=	< > <= >=
	== !=	== !=
Logical	! &&	not and
	||	or
Ternary	(expr1) ? <expr2> : <expr3>	(expr1) if <expr2> then <expr3>
Assignment	= += -= *= /= %=	= += -= *= /= %= **=
Identity/Membership		is is not in not in

• Java: boolean q = (5 % 2 != 2) ? true : false
• Python: q = True if (5 % 2 != 2) else False

Standard Input

import java.util.Scanner;

public class Inputs {
  static Scanner in = new Scanner(System.in);

  public static void main(String[] args) {
    System.out.print("X = ");
    int x = in.nextInt();
    System.out.println("x squared = " + Math.pow(x, 2));
  }
}

import sys

x = int(input("x = "))

print("x squared = ", pow(x, 2))

String

String (java)

Immutable

• String s1 = "Hello";: initialize using literal syntax
• String s2 = new String("Hello");: initialize using a constructor

s1 == s1 // false
s1.equals(s2) // true

String Format (Python)

Symbol	Meaning	Example code	Output
<	Left align	f'[{42:<5}]'	[42 ]
>	Right align	f'[{42:>5}]'	[ 42]
^	Center align	f'[{42:^5}]'	[ 42 ]
< with fill char	Left align with custom fill	f'[{42:-<5}]'	[42---]
> with fill char	Right align with custom fill	f'[{42:->5}]'	[---42]
^ with fill char	Center align with custom fill	f'[{42:->5}]'	[-42--]

Array

Array (java)

int[] x = {2, 4, -1, 11, 3};

• Declaration: int[] x
• Instantiation: x = new int[5];
• Initialization: x[0] = 2; x[1] = 4; x[2] = -1;