Review

• Java if statements, operators, and variables are fundamental concepts in Java programming.

Variables in Java

• Variables are containers for storing data values.
• Each variable in Java must have a specific data type, which determines the size and type of values that can be stored in the variable.
• Before you can use a variable, you need to declare it.
• Variable declaration involves specifying the variable's name and data type.
• Syntax: dataType variableName;
• Example: int age; declares an integer variable named age.

Data Types

• Java has several built-in data types, which are divided into primitive and non-primitive data types.

Primitive Data Types

• Primitive data types are the most basic data types in Java.
• They include:
  • byte: Stores whole numbers from -128 to 127.
  • short: Stores whole numbers from -32,768 to 32,767.
  • int: Stores whole numbers from -2,147,483,648 to 2,147,483,647.
  • long: Stores whole numbers from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807.
  • float: Stores single-precision floating-point numbers.
  • double: Stores double-precision floating-point numbers.
  • boolean: Stores true or false values.
  • char: Stores single characters (letters, digits, symbols).

Non-Primitive Data Types

• Non-primitive data types are also known as reference types because they store references to memory locations.
• Examples include Strings, Arrays, Classes, and Interfaces.
• Non-primitive types are created by the programmer except String.

Variable Assignment

• After declaring a variable, you can assign a value to it using the assignment operator (=).
• Syntax: variableName = value;
• Example: age = 30; assigns the value 30 to the age variable.
• You can also declare and initialize a variable in the same line.
• Example: int age = 30;

Operators in Java

• Operators are symbols that perform operations on variables and values.
• Java provides a rich set of operators, including arithmetic, relational, logical, and assignment operators.

Arithmetic Operators

• Perform basic arithmetic operations.
  • +: Addition
  • -: Subtraction
  • *: Multiplication
  • /: Division
  • %: Modulus (remainder)
• Example:
  • int sum = 10 + 5; (sum is 15)
  • int remainder = 10 % 3; (remainder is 1)

Relational Operators

• Compare two values and return a boolean result (true or false).
  • ==: Equal to
  • !=: Not equal to
  • >: Greater than
  • <: Less than
  • >=: Greater than or equal to
  • <=: Less than or equal to
• Example:
  • boolean isEqual = (5 == 5); (isEqual is true)
  • boolean isGreater = (10 > 5); (isGreater is true)

Logical Operators

• Combine multiple boolean expressions.
  • &&: Logical AND (true if both operands are true)
  • ||: Logical OR (true if at least one operand is true)
  • !: Logical NOT (true if the operand is false)
• Example:
  • boolean result = (true && false); (result is false)
  • boolean result2 = (true || false); (result2 is true)
  • boolean result3 = !true; (result3 is false)

Assignment Operators

• Assign values to variables.
  • =: Simple assignment
  • +=: Add and assign
  • -=: Subtract and assign
  • *=: Multiply and assign
  • /=: Divide and assign
  • %=: Modulus and assign
• Example:
  • int x = 10;
  • x += 5; (x is now 15)

Increment and Decrement Operators

• Increment or decrement the value of a variable by 1.
  • ++: Increment
  • --: Decrement
• Can be used as prefix or postfix.
• Example:
  • int x = 5;
  • x++; (x is now 6)
  • ++x; (x is now 7)
  • int y = x++; (y is 7, x is 8)
  • int z = ++x; (z is 9, x is 9)

If Statements in Java

• If statements allow you to execute a block of code only if a certain condition is true.
• Java supports several forms of if statements:
  • if statement
  • if-else statement
  • if-else if-else statement

If Statement

• Executes a block of code if the condition is true.
• Syntax:

  if (condition) {
      // Code to execute if the condition is true
  }
  

• Example:

  int age = 20;
  if (age >= 18) {
      System.out.println("You are an adult.");
  }
  

If-Else Statement

• Executes one block of code if the condition is true and another block of code if the condition is false.
• Syntax:

  if (condition) {
      // Code to execute if the condition is true
  } else {
      // Code to execute if the condition is false
  }
  

• Example:

  int age = 16;
  if (age >= 18) {
      System.out.println("You are an adult.");
  } else {
      System.out.println("You are a minor.");
  }
  

If-Else If-Else Statement

• Allows you to check multiple conditions in a sequence.
• Syntax:

  if (condition1) {
      // Code to execute if condition1 is true
  } else if (condition2) {
      // Code to execute if condition2 is true
  } else {
      // Code to execute if all conditions are false
  }
  

• Example:

  int score = 75;
  if (score >= 90) {
      System.out.println("A");
  } else if (score >= 80) {
      System.out.println("B");
  } else if (score >= 70) {
      System.out.println("C");
  } else {
      System.out.println("D");
  }
  

Nested If Statements

• You can also nest if statements inside other if statements.
• This allows you to create more complex decision-making logic.
• Example:

  int age = 25;
  boolean hasLicense = true;
  if (age >= 18) {
      if (hasLicense) {
          System.out.println("You can drive.");
      } else {
          System.out.println("You need a license to drive.");
      }
  } else {
      System.out.println("You are too young to drive.");
  }
  

Ternary Operator

• Shorthand for a simple if-else statement.
• Syntax: condition ? valueIfTrue : valueIfFalse;
• Example:

  int age = 20;
  String message = (age >= 18) ? "You are an adult." : "You are a minor.";
  System.out.println(message);
  

Scope of Variables

• The scope of a variable refers to the region of the code where the variable is accessible.
• Variables declared inside a block (e.g., within an if statement) are only accessible within that block.
• Example:

  if (true) {
      int x = 10; // x is only accessible inside this if block
      System.out.println(x);
  }
  // System.out.println(x); // This would cause an error because x is out of scope