How do abstract classes and interfaces differ in modern Java?

Explanation & Concept

• Abstract Classes: Represent an 'is-a' relationship. Can define instance fields, state, and constructors, and classes can only inherit from one abstract class (single inheritance). • Interfaces: Represent a 'can-do' capability contract. Classes can implement multiple interfaces. Since Java 8, interfaces can contain `default` and `static` methods, and Java 9 added `private` methods.

Code Example

java

public interface Auditable {
    // Default method provides default behavior without breaking implementers
    default void logAudit(String action) {
        System.out.println("AUDIT [" + System.currentTimeMillis() + "]: " + action);
    }
}

public abstract class BaseEntity {
    private final String id;
    public BaseEntity(String id) { this.id = id; }
    public String getId() { return id; }
}

public class Order extends BaseEntity implements Auditable {
    public Order(String id) { super(id); }
}

How It Works & Key Takeaways

Java allows multiple interface inheritance, letting `Order` inherit identity from `BaseEntity` while adopting auditing capabilities from `Auditable`.

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java

How do abstract classes and interfaces differ in modern Java?

Explanation & Concept

Code Example

java

public interface Auditable {
    // Default method provides default behavior without breaking implementers
    default void logAudit(String action) {
        System.out.println("AUDIT [" + System.currentTimeMillis() + "]: " + action);
    }
}

public abstract class BaseEntity {
    private final String id;
    public BaseEntity(String id) { this.id = id; }
    public String getId() { return id; }
}

public class Order extends BaseEntity implements Auditable {
    public Order(String id) { super(id); }
}

How It Works & Key Takeaways

Java allows multiple interface inheritance, letting `Order` inherit identity from `BaseEntity` while adopting auditing capabilities from `Auditable`.

Mock Test · 1 Questions · Optional

Ready for Exception Handling?

Take a quick test to evaluate yourself, or move straight to the next module.

Beginner2 questions

Skip