Differences and applications of abstract classes and interfaces in Java language

Differences and Applications of Abstract Classes and Interfaces in Java Language

In Java language, abstract classes and interfaces are two important concepts. They all share abstract characteristics, but there are also some obvious differences between them. When using Java language for programming, choosing to use abstract classes or interfaces has an important impact on the structural design and scalability of the program.

Abstract class

In the Java language, an abstract class refers to a class that contains abstract methods. Abstract methods refer to methods that have no specific implementation in the method declaration. For example:

abstract class Shape{
  public abstract void draw();
  public abstract void resize();
}

Abstract classes cannot be instantiated and can only be inherited. Subclasses must implement all abstract methods in the abstract class, unless the subclass is also an abstract class.

The purpose of an abstract class is to provide a basic class that can provide certain common methods and attributes for subclasses. At the same time, subclasses can implement or rewrite these methods according to their own needs, which has a certain degree of flexibility. sex.

When we need to design a class with polymorphic properties, abstract classes are a good choice. For example:

abstract class Animal{
  public abstract void move();
}
class Cat extends Animal{
  public void move(){
    System.out.println("跑");
  }
}
class Dog extends Animal{
  public void move(){
    System.out.println("走");
  }
}

In the above code, we created an abstract class Animal, which has an abstract method move(), and we created two subclasses Cat and Dog that implement this method. We can obtain their respective move() methods by instantiating Cat and Dog objects. Since they are all subclasses of the Animal class, they can be referenced through variables of type Animal.

Interface

In the Java language, the interface is a special abstract class with the following characteristics:

• The interface cannot be instantiated, but can only be implemented .
• The methods defined in the interface must be public abstract methods.
• The properties defined in the interface must be public static constants.
• An interface can inherit multiple interfaces.

The purpose of interfaces is to create common classes and components. For example:

interface Drawable{
  public void draw();
}
interface Resizable{
  public void resize();
}
class Circle implements Drawable, Resizable{
  private int radius;
  public void draw(){
    System.out.println("绘制圆形");
  }
  public void resize(){
    System.out.println("重设圆形大小");
  }
}

In the above code, we created two interfaces, Drawable and Resizable, and defined a common method draw() and resize(). Then, we created a Circle class that implemented these two interfaces, and implemented the draw() and resize() methods in the Circle class. In this way, when drawing a circle, you can directly use an instance of the Circle class.

Summary

Abstract classes and interfaces are important concepts in the Java language and are often used in programming. They can all provide abstract templates and common methods to help program designers complete the design of program structure and components.

The specific application of abstract classes and interfaces can be selected according to specific circumstances. If you need to design a class with a specific implementation, you can use an abstract class; if you need to design a general class or component, you can use an interface. In specific use, it needs to be designed according to actual needs to achieve optimal program effects.

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