Introduction

• "Is it raining ?"
  • "No" - Then lets play cricket.
  • "Yes" - Ohh, we cant play cricket.
• Just like in real life, in programming also, we face situations where we need to make decisions based on certain conditions.

• In Java, we use conditional statements to decide which part of the code should run depending on the condition.
• Conditional Statments helps us to:
  • Control the flow of the program.
  • Decide which block of code should be executed when certain conditions are met.

• Examples of Conditional Statements in Java:
  1. if: Runs code if a condition is true.
  2. if-else: Runs one block of code if true, and another block if false.
  3. if-else if ladder: Checks multiple conditions one by one and runs the block of code for the first true condition.
  4. switch: Chooses a block of code to run based on specific cases.
  These are explained deeply as below:

"if" Statement in Java

• The if statement in Java evaluates a boolean condition.
• If the condition is true, the block of code inside the if statement is executed.
• Syntax:

  if(condition)
  {
      // this block will be executed if the condition is true
  }

• Program:

  public class IfExample
  {
      public static void main(String[] args)
      {
          int number = 10;
  
          // Check if the number is positive
          if (number > 0)
          {
              System.out.println("The number is positive.");
          }
      }
  }

  Output:

  The number is positive.

• NOTE :

  • If there is only one statement in if block, then curly braces {} are optional.
  • Syntax :

    if(condition)
        statement;

  • Example :

    public class IfExample
    {
        public static void main(String[] args)
        {
            int number = 10;
    
            if (number > 0)
                System.out.println("The number is positive.");
        }
    }

"if-else" Statement in Java

• The if-else statement in Java evaluates a boolean condition.
• If the condition is true, the block of code inside the if is executed; otherwise, the code inside the else block runs.
• Syntax:

  if(condition)
  {
      // this block will be executed if the condition is true
  }
  else
  {
      // this block will be executed if condition is false   
  }

• Program:

  public class IfElseExample
  {
      public static void main(String[] args)
      {
          int number = -5;
  
          // Check if the number is positive or negative
          if (number > 0)
          {
              System.out.println("The number is positive.");
          }
          else
          {
              System.out.println("The number is negative.");
          }
      }
  }

  Output:

  The number is negative.

• NOTE :

  • If there is only one statement in if-else block, then curly braces {} are optional.
  • Syntax :

    if(condition)
        statement;
    else
        statement;

"if-else if" Ladder Statement in Java

• The if-else if ladder in Java evaluates multiple boolean conditions in sequence.
• If any of the condition is true, the block of code associated with that condition is executed; if none of the conditions are true, the optional else block runs.
• Syntax:

  if (condition1) 
  {
      // Code to execute if condition1 is true
  }
  else if (condition2)
  {
      // Code to execute if condition2 is true
  }
  // ---- more else-if blocks as needed ----
  else
  {
      // Code to execute if none of the above conditions are true
  }

• Program:

  public class IfElseIfLadderExample
  {
      public static void main(String[] args)
      {
          int marks = 75;
  
          // Determine the grade based on marks
          if (marks >= 90)
          {
              System.out.println("Grade: A");
          }
          else if (marks >= 75)
          {
              System.out.println("Grade: B");
          }
          else if (marks >= 50)
          {
              System.out.println("Grade: C");
          }
          else
          {
              System.out.println("Grade: F");
          }
      }
  }

  Output:

  Grade: B

"switch" Statement in Java

• The switch statement in Java runs one block of code based on matching a condition.
• It checks multiple cases for a value and runs the matching case.
• If no case matches, the optional default block runs.
• Syntax:

  switch (expression)
  {
      case value1:
          // Code to execute if expression equals value1
          break;
      case value2:
          // Code to execute if expression equals value2
          break;
      // ---- more cases as needed ----
      default:
          // Code to execute if no case matches (optional)
          break;
  }

• NOTE : Instead of writing many if-else statements, we can use the switch statement for simpler code.
• Program:

  public class SwitchExample
  {
      public static void main(String[] args)
      {
          int day = 3;
  
          // Determine the day of the week
          switch (day)
          {
              case 1:
                  System.out.println("Monday");
                  break;
              case 2:
                  System.out.println("Tuesday");
                  break;
              case 3:
                  System.out.println("Wednesday");
                  break;
              case 4:
                  System.out.println("Thursday");
                  break;
              case 5:
                  System.out.println("Friday");
                  break;
              case 6:
                  System.out.println("Saturday");
                  break;
              case 7:
                  System.out.println("Sunday");
                  break;
              default:
                  System.out.println("Invalid day");
          }
      }
  }

  Output:

  Wednesday