Correct way to write Java interface class

How to correctly write a Java interface class requires specific code examples

In Java, an interface is an abstract type that defines a set of related methods. The interface does not implement these methods, but is implemented by the class that implements the interface. Writing correct interface classes is one of the keys to Java programming. The following will introduce how to correctly write Java interface classes and give some specific code examples.

1. Basic concepts and characteristics of interfaces
Before starting to write Java interface classes, you first need to understand the basic concepts and characteristics of interfaces.

1.1 Concept
The interface is a purely abstract type that only defines the signature of a set of methods without a specific implementation. Through interfaces, features such as program modularization, decoupling, and polymorphism can be achieved.

1.2 Features

• Interfaces are defined using the "interface" keyword, and member attributes such as method signatures and constants can be declared in the interface.
• Methods in the interface default to public abstract type, and constants default to public static final type.
• A class can implement multiple interfaces.
• Interfaces can inherit other interfaces.

2. Things to note when writing interfaces
When writing interface classes, you need to pay attention to the following aspects.

2.1 Naming specifications
The naming of interfaces should be clear, accurate, and concise, and usually use camel case naming. Interface names generally begin with the capital letter "I".

2.2 Method signature
The method signature in the interface should be clear and consistent with actual needs. The following rules should generally be followed:

• The naming of methods should be verbs or verb phrases.
• The return type of a method should be a concrete type, not an interface or abstract type.
• The parameters of the method should be abstract types or interface types.

2.3 Constant declaration
The constants in the interface should be the constants used by related methods, usually named with uppercase letters and underscores.

2.4 Design principles of interfaces
The design of interfaces should follow the following principles:

• Single responsibility principle: An interface should only define a set of related methods.
• Opening and closing principle: The design of the interface should be abstract enough to be used by multiple implementation classes, and at the same time it should be open to extension, that is, it can be extended by inheriting the interface.
• Interface isolation principle: The interface should be as small and precise as possible, and avoid defining too many irrelevant methods.
• Dependency inversion principle: rely on abstract rather than concrete implementation classes.

3. Sample code of Java interface class
The following is a specific sample code of Java interface class.

public interface Shape {
    double getArea();
    double getPerimeter();
}

public class Circle implements Shape {
    private double radius;

    public Circle(double radius) {
        this.radius = radius;
    }

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

    public double getPerimeter() {
        return 2 * Math.PI * radius;
    }
}

public class Rectangle implements Shape {
    private double width;
    private double height;

    public Rectangle(double width, double height) {
        this.width = width;
        this.height = height;
    }

    public double getArea() {
        return width * height;
    }

    public double getPerimeter() {
        return 2 * (width + height);
    }
}

public class Main {
    public static void main(String[] args) {
        Circle circle = new Circle(5);
        System.out.println("Circle Area: " + circle.getArea());
        System.out.println("Circle Perimeter: " + circle.getPerimeter());

        Rectangle rectangle = new Rectangle(4, 6);
        System.out.println("Rectangle Area: " + rectangle.getArea());
        System.out.println("Rectangle Perimeter: " + rectangle.getPerimeter());
    }
}

The above code defines an interface Shape. The Shape interface has two method signatures: getArea() and getPerimeter(). Both the Circle and Rectangle classes implement the Shape interface and implement these two methods respectively. In the Main class, we can call methods in the interface by instantiating the Circle and Rectangle classes.

Through the above example code, we can see how the interface is used: defining the interface, implementing the interface and implementing the methods in the interface, and referencing specific implementation class objects through the interface. This makes our programs more flexible, scalable, and easier to maintain.

Summary
This article introduces how to correctly write Java interface classes and gives specific code examples. To write a correct interface class, you need to pay attention to the interface naming convention, method signatures, constant declarations, and interface design principles. Through reasonable use of interfaces, programs can be made more flexible, scalable, and easier to maintain. Hope this article is helpful to you.

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