How to understand the characteristics of interfaces and abstract classes in Java

The difference between interfaces and abstract classes: Interfaces can only contain abstract methods, while abstract classes can contain abstract methods and implemented methods. Interfaces cannot be instantiated, whereas abstract classes can be inherited and their subclasses instantiated. Methods in an interface implicitly have public and abstract access, whereas methods in an abstract class require explicitly specified access and abstraction.

In-depth understanding of interfaces and abstract classes in Java

Introduction

Interface and abstract classes are crucial concepts in Java programming. They provide an extension to Java's object-oriented paradigm, allowing the creation of flexible and reusable code. This article will explore the characteristics of interfaces and abstract classes and provide practical examples to solidify understanding.

Interface

Definition: An interface is a reference type that defines the methods that an object can have, but it does not provide these methods accomplish. The methods in an interface are abstract, meaning they must be implemented in the class that implements the interface.

Features:

• Interface cannot be instantiated.
• Interfaces can only contain abstract methods and static constants.
• All methods in the interface are public and abstract.

Practical case

// 定义一个名为 Shape 的接口
public interface Shape {
    double getArea();
    double getPerimeter();
}

Abstract class

Definition: Abstract class cannot Directly instantiated classes. It provides a definition of the object's behavior and can contain both abstract and concrete methods (implemented methods).

Features:

• Abstract classes can contain abstract methods and concrete methods.
• Abstract classes cannot be instantiated and can only be inherited by subclasses.
• If a class inherits an abstract class, it must implement all abstract methods in the abstract class, otherwise the class itself must be an abstract class.

Practical case

// 定义一个名为 Animal 的抽象类
public abstract class Animal {
    private String name;
    
    public abstract void speak();
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
}

The difference between interface and abstract class

• Interface can only contain abstraction Methods, while abstract classes can contain both abstract methods and concrete methods.
• Interfaces cannot be instantiated, while abstract classes can be inherited and their subclasses instantiated.
• Methods in interfaces implicitly have public and abstract access rights, while methods in abstract classes require explicitly specified access rights and abstraction.

Conclusion

Interfaces and abstract classes are powerful tools in Java that allow the creation of flexible and reusable code. By understanding their characteristics and differences, developers can design and implement more efficient and maintainable software.

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