Java Control Statements Lecture Notes

Overview of Control Statements

• Control statements allow for conditional execution of code based on specific conditions.
• Regular Java program execution occurs top to bottom, but control statements change execution flow.

Types of Control Statements

1. Conditional Statements: Execute statements based on conditions.
2. Looping Statements: Repeat the execution of a block of code multiple times.
3. Jumping Statements: Control the flow of execution in various ways (e.g. break, continue).

Conditional Statements

Purpose

• To execute specific statements based on certain conditions.

Types of Conditional Statements in Java

1. If Statement: Simple conditional execution.
2. If-Else Statement: Conditional execution with an alternative path.
3. Nested If-Else Statement: If-Else conditions nested within each other.
4. Switch Statement: An alternative to multiple if-else for handling multiple conditions based on a variable.

If Statement Syntax

• Syntax:

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

If-Else Statement Syntax

• Syntax:

  if (condition) {
      // if true
  } else {
      // if false
  }
  

• If-Else allows for an alternative execution path if the condition is false.

Example of If Statement

• Checking if a person is eligible for voting:

  int personAge = 25;
  if (personAge >= 18) {
      System.out.println("Eligible for voting");
  }
  

• If age is less than 18, no output will occur.

Example of If-Else Statement

• Check if a number is even or odd:

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

Nested If-Else Example

• Checking if a number is positive, negative or zero:

  if (number > 0) {
      System.out.println("Positive");
  } else if (number < 0) {
      System.out.println("Negative");
  } else {
      System.out.println("Zero");
  }
  

Switch Statement

Syntax

• Syntax:

  switch (variable) {
      case value1:
          // statements
          break;
      case value2:
          // statements
          break;
      default:
          // statements
  }
  

Purpose

• Use when you have multiple conditions to check against a single variable.
• Reduces the lines of code compared to multiple if-else statements.

Example of Switch Statement

• Displaying day names based on the week number:

  switch (weekNumber) {
      case 1:
          System.out.println("Sunday");
          break;
      case 2:
          System.out.println("Monday");
          break;
      // Additional cases...
      default:
          System.out.println("Invalid week number");
  }
  

Break Statement

• Used to exit the switch case block after executing a matching case.
• Recommended to prevent falling through to subsequent cases.

Summary

• Control statements allow us to modify the execution flow based on conditions.
• Java provides various types of control statements (conditional, looping, jumping) to handle different scenarios effectively.

Assignments

1. Find the largest of two numbers using both if-else and ternary operator.
2. Find the smallest of three numbers using if-else conditions.
3. Write a program to take the name of the week and return its corresponding number using a switch case.