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Java supports single inheritance through the extends keyword, where a subclass inherits non-private fields and methods from one superclass, enabling code reuse and hierarchical relationships; for example, a Dog class extending Animal can access its eat() method while adding its own bark() method; subclasses can override inherited methods using the @Override annotation to provide specific implementations, such as Cat overriding makeSound(); the super keyword allows calling the parent constructor (super()), accessing overridden methods (super.methodName()), or parent fields; constructors are not inherited but the superclass constructor is automatically invoked during subclass instantiation, requiring explicit super(...) calls if no default constructor exists; access modifiers determine inheritance visibility: private members are inaccessible, protected and package-private members are accessible within subclasses (with package restrictions for the latter), and public members are fully accessible; all Java classes implicitly extend java.lang.Object, inheriting methods like toString(), equals(), and hashCode(); while inheritance promotes reusability, it should be used carefully to avoid tight coupling, with composition preferred in some cases—overall, Java inheritance follows a one-parent rule with shared behavior and specialization through overriding and access control.
Inheritance in Java allows one class to inherit fields and methods from another class, promoting code reuse and establishing a hierarchical relationship between classes. It’s a core concept of object-oriented programming (OOP) and is implemented using the extends keyword.
Single Inheritance with the extends Keyword
Java supports single inheritance, meaning a class can extend only one other class. When a class inherits from another, it gains access to all non-private fields and methods (depending on access modifiers like public, protected, and package-private).
class Animal {
void eat() {
System.out.println("This animal eats food.");
}
}
class Dog extends Animal {
void bark() {
System.out.println("The dog barks.");
}
}Now, an instance of Dog can call both eat() (inherited from Animal) and bark() (defined in Dog):
Dog myDog = new Dog(); myDog.eat(); // Inherited method myDog.bark(); // Own method
Method Overriding and the @Override Annotation
A subclass can provide a specific implementation of a method already defined in its superclass. This is called method overriding.
class Animal {
void makeSound() {
System.out.println("Animal makes a sound");
}
}
class Cat extends Animal {
@Override
void makeSound() {
System.out.println("Cat meows");
}
}When you call makeSound() on a Cat object, the overridden version in Cat runs. The @Override annotation is optional but recommended—it helps catch errors at compile time if the method doesn’t actually override anything.
The super Keyword
The super keyword refers to the immediate parent class. It can be used to:
- Call the parent class constructor:
super() - Access overridden methods:
super.methodName() - Access parent class fields
class Bird extends Animal {
String species;
Bird(String species) {
super(); // Calls Animal's constructor
this.species = species;
}
@Override
void eat() {
super.eat(); // Reuse parent's eat() behavior
System.out.println("This bird eats seeds.");
}
}Inheritance and Constructors
Constructors are not inherited. However, when creating a subclass object, the superclass constructor is automatically called first (using super()). If not explicitly written, the compiler inserts a call to the no-argument superclass constructor.
If the superclass doesn’t have a no-argument constructor, you must explicitly call a superclass constructor using super(...) as the first line in the subclass constructor.
Key Points About Access Modifiers
privatemembers: Not accessible in subclassesprotectedmembers: Accessible in subclasses, even across packages- Package-private (default) members: Accessible only within the same package
publicmembers: Accessible everywhere
The Object Class: Universal Superclass
All classes in Java implicitly extend the java.lang.Object class if no other superclass is specified. This means every class has basic methods like toString(), equals(), hashCode(), and clone().
class Person {
// Automatically extends Object
}Final Words
Inheritance helps build a clear hierarchy and promotes reusability, but it should be used thoughtfully. Overuse can lead to tightly coupled code. Favor composition over inheritance when appropriate.
Basically, Java inheritance is straightforward: one parent, one child, shared behavior, and the ability to specialize—just remember the rules around access, constructors, and overriding.
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