03-java-control-structures.md

Java Control Structures

In Java, control structures are used to manage the flow of a program. These structures include decision-making statements and loops.

Decision-Making Statements

1. if Statement:

• Used to execute a block of code if the specified condition is true.

  int x = 10;
  if (x > 5) {
      System.out.println("x is greater than 5");
  }

2. if-else Statement:

• Executes one block of code if the condition is true and another if it's false.

  int y = 3;
  if (y % 2 == 0) {
      System.out.println("y is even");
  } else {
      System.out.println("y is odd");
  }

3. switch Statement:

• Used to select one of many code blocks to be executed.

  int day = 2;
  switch (day) {
      case 1:
          System.out.println("Monday");
          break;
      case 2:
          System.out.println("Tuesday");
          break;
      // ... other cases ...
      default:
          System.out.println("Invalid day");
  }

4. Loops

1. for Loop:

• Executes a block of code a specified number of times.

  for (int i = 0; i < 5; i++) {
      System.out.println("Iteration: " + i);
  }

2. while Loop:

• Repeats a block of code while a specified condition is true.

  int count = 0;
  while (count < 3) {
      System.out.println("Count: " + count);
      count++;
  }

3. do-while Loop:

• Similar to the while loop, but the code block is executed at least once.

  int num = 5;
  do {
      System.out.println("Number: " + num);
      num--;
  } while (num > 0);

4. Enhanced For Loop:

• Iterating through an array of strings using the enhanced for loop.

      public static void main(String[] args) {
          String[] fruits = {"Apple", "Banana", "Orange", "Grapes"};
  
          // Using enhanced for loop to iterate over the array of strings
          for (String fruit : fruits) {
              System.out.println(fruit);
          }
      }

5. Iterator with a List of Objects:

• Using an iterator to iterate through a list of custom objects.

  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.List;
  
  class Person {
      String name;
  
      public Person(String name) {
          this.name = name;
      }
  }
  
  public class IteratorExample {
      public static void main(String[] args) {
          List<Person> people = new ArrayList<>();
          people.add(new Person("Alice"));
          people.add(new Person("Bob"));
          people.add(new Person("Charlie"));
  
          // Using iterator to iterate through the list of Person objects
          Iterator<Person> iterator = people.iterator();
          while (iterator.hasNext()) {
              Person person = iterator.next();
              System.out.println(person.name);
          }
      }
  }

6. Streams with a List of Names:

• Using streams to filter and print elements from a list of names.

  import java.util.Arrays;
  import java.util.List;
  
  public class StreamsExample {
      public static void main(String[] args) {
          List<String> names = Arrays.asList("John", "Alice", "Bob", "Charlie", "Eve");
  
          // Using streams to filter and print names starting with 'A'
          names.stream()
                .filter(name -> name.startsWith("A"))
                .forEach(System.out::println);
      }
  }