Java Programming Unit 2: Control Flow and Arrays

Study Notes

Definition: A variable is a named storage location that holds a value of a specific type, used to store and manipulate data in Java.
Local Variables:
- Declared within a method, constructor, or block.
- Accessible only within their defined scope.
- Must be initialized before use.
- Example: In LocalVariableExample, int age = 25; is a local variable.
Instance Variables (Non-Static Variables):
- Declared within a class but outside any methods, constructors, or blocks.
- Each class instance has its own copy.
- Initialized with default values if not explicitly assigned.
- Example: In InstanceVariableExample, String name; is an instance variable accessible via the class object, like obj.name = "John";.
Class Variables (Static Variables):
- Declared with the static keyword within a class.
- There is only one copy shared among all instances of the class.
- Initialized with default values if not explicitly assigned.
- Example: In ClassVariableExample, static int count; can be accessed using the class name, ClassVariableExample.count = 10;.

Type Casting: Refers to converting a value from one data type to another, which exists in two forms: implicit (widening) and explicit (narrowing).
Implicit Casting (Widening):
- Automatic conversion occurs when assigning a smaller data type to a larger data type.
- Example: int myInt = 10; double myDouble = myInt; performs implicit casting from int to double.
Explicit Casting (Narrowing):
- Conversion from a higher data type to a lower data type, needing explicit declaration by the programmer.
- Example: double myDouble = 10.5; int myInt = (int) myDouble; demonstrates explicit casting from double to int.
Type Conversion:
- The process of converting data between data types, encompassing both primitive and reference types.
Converting String to int:
- Example: String numberString = "123"; int number = Integer.parseInt(numberString); captures how a string can be converted to an integer.
Converting int to String:
- The process typically involves methods like String.valueOf(int) or Integer.toString(int).