Logic Instructions

Statement	Use for
if	Run code if a condition is true
if-else	Choose between two alternatives
if-else if	Handle multiple conditions
switch	Match exact values (cleaner than many if chains)

1. If Statement

• Syntax:

  if (condition) {
    // code to execute if condition is true
  }
  

• Example:

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

  2. If-else Statement

• Syntax: Chỉnh sửa if (condition) { // if true } else { // if false }
• Example:

  int number = 7;
  if (number % 2 == 0) {
    System.out.println("Even");
  } else {
    System.out.println("Odd");
  }
  

  3. If-else if-else chain

• Syntax:

  if (condition1) {
    // if condition1 true
  } else if (condition2) {
    // if condition2 true
  } else {
    // if none true
  }
  

• Example:

  int score = 85;
  if (score >= 90) {
    System.out.println("Grade A");
  } else if (score >= 75) {
    System.out.println("Grade B");
  } else {
    System.out.println("Grade C");
  }
  

  4. Switch Statement

  Used when you have multiple exact matches for a single variable (usually int, char, String, or enum).

• Syntax:

  switch (expression) {
    case value1:
        // code block
        break;
    case value2:
        // code block
        break;
    default:
        // code if no match
  }
  

• Example:

  int day = 3;
  switch (day) {
    case 1:
        System.out.println("Monday");
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    case 3:
        System.out.println("Wednesday");
        break;
    default:
        System.out.println("Other day");
  }
  

  Important Notes:

  • break is used to exit the switch after a case matches.
  • default is optional and runs if no cases match.

Code Demo

public class LogicInstructions {
    public static void main(String[] args) {
        int number = 75;

        // if-else if
        if (number >= 90) {
            System.out.println("Excellent");
        } else if (number >= 60) {
            System.out.println("Good");
        } else {
            System.out.println("Needs Improvement");
        }

        // switch
        String grade;
        switch (number / 10) {
            case 10:
            case 9:
                grade = "A";
                break;
            case 8:
                grade = "B";
                break;
            case 7:
                grade = "C";
                break;
            case 6:
                grade = "D";
                break;
            default:
                grade = "F";
        }
        System.out.println("Grade: " + grade);
    }
}

Output:

Good
Grade: C