Return Types

Every method in Java must declare a return type, which specifies what kind of value the method will return to the caller.

Void Return Type

When a method doesn’t return any value, use void:

public void printMessage(String message) {
  System.out.println(message);
  // No return statement needed
}

Primitive Return Types

Methods can return any primitive data type:

public int add(int a, int b) {
  return a + b;
}

public double calculateArea(double radius) {
  return Math.PI * radius * radius;
}

public boolean isAdult(int age) {
  return age >= 18;
}

public char getFirstCharacter(String text) {
  if (text != null && text.length() > 0) {
    return text.charAt(0);
  }
  return '\0'; // null character
}

Reference Return Types

Methods can return objects (reference types):

public String formatName(String firstName, String lastName) {
  return lastName + ", " + firstName;
}

public Date getCurrentDate() {
  return new Date();
}

public int[] getEvenNumbers(int count) {
  int[] result = new int[count];
  for (int i = 0; i < count; i++) {
    result[i] = i * 2;
  }
  return result;
}

The return Statement

• The return statement exits the method immediately
• For non-void methods, a return statement with a value is required
• Multiple return statements are allowed

public String getLetterGrade(int score) {
  if (score >= 90) return "A";
  if (score >= 80) return "B";
  if (score >= 70) return "C";
  if (score >= 60) return "D";
  return "F";
}

Return Type Compatibility

The returned value must be compatible with the declared return type:

public int getNumber() {
  return 42;       // OK
  // return 3.14;  // Error: double cannot be converted to int
  // return "42";  // Error: String cannot be converted to int
}

public Object getObject() {
  return "Hello";  // OK: String is a subclass of Object
  // return 42;    // OK: autoboxed to Integer which is a subclass of Object
}

Covariant Return Types

When overriding methods, the return type can be a subclass of the original return type:

class Animal { }
class Dog extends Animal { }

class AnimalShelter {
  public Animal getAnimal() {
    return new Animal();
  }
}

class DogShelter extends AnimalShelter {
  @Override
  public Dog getAnimal() {  // Covariant return type
    return new Dog();
  }
}

Common Patterns

Returning Optional Values

public Optional<User> findUserById(int id) {
  User user = database.lookup(id);
  return Optional.ofNullable(user);
}

Chaining Method Calls

public class StringBuilder {
  public StringBuilder append(String str) {
    // append the string
    return this;  // Return this object for chaining
  }
}

// Usage
new StringBuilder()
  .append("Hello")
  .append(" ")
  .append("World");

Returning Status or Result Objects

public class Result {
  private final boolean success;
  private final String message;
  private final Object data;

  // constructor and getters
}

public Result saveUser(User user) {
  try {
    database.save(user);
    return new Result(true, "User saved successfully", user);
  } catch (Exception e) {
    return new Result(false, e.getMessage(), null);
  }
}