Java Programming Unit 2: Control Flow and Arrays

Variables and Their Types

• 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 and Conversion

• 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).

This quiz covers Unit 2 of Java Programming, focusing on control flow and arrays, including the concept of variables and their types. Test your understanding of local variables and how they are used to manage data within Java programs.