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What is the inheritance of the class in java? Analysis of the inheritance relationship and implementation method of the class
What is the inheritance of the class in java? Analysis of the inheritance relationship and implementation method of the class
May 28, 2025 pm 05:39 PM
Classes in Java inherit from Object class by default unless they are explicitly inherited. 1. The Java class is directly or indirectly inherited from the Object class. 2. Class inheritance is implemented through the extends keyword, and the interface is implemented through the implements keyword. 3. The subclass constructor calls the parent class constructor first, and pay attention to the call order. 4. Java does not support multiple inheritance, but similar effects can be achieved through interfaces. 5. Combination should be used as much as possible instead of inheritance, keep the inheritance level simple and reduce the degree of class coupling.
public class Shape {
public void draw() {
System.out.println("Drawing a shape");
}
}
public class Circle extends Shape {
@Override
public void draw() {
System.out.println("Drawing a circle");
}
}
public class Rectangle extends Shape {
@Override
public void draw() {
System.out.println("Drawing a rectangle");
}
}
In this example, both the Circle and Rectangle classes inherit the Shape class and override the draw method. This is the embodiment of polymorphism. Subclasses can rewrite the parent class's methods according to their own needs. But in actual development, inheritance is not omnipotent. Sometimes abuse of inheritance will increase the complexity of the code. For example, I once used deep inheritance in a project, which resulted in too high coupling between classes, which was very difficult to maintain. Later I realized that we should try to use combination rather than inheritance to achieve reuse of the code. Let’s talk about the implementation method, inheritance in Java can be implemented through the extends keyword. For example, in the example above, the Circle class uses extends Shape to indicate that it inherits from the Shape class. Also, if we want to implement the interface, we can use the implements keyword. for example:
public interface Drawable {
void draw();
}
public class Circle extends Shape implements Drawable {
@Override
public void draw() {
System.out.println("Drawing a circle");
}
}
Here, the Circle class not only inherits the Shape class, but also implements the Drawable interface. In actual development, I found that a mistake many developers are prone to make when using inheritance is to ignore the order of call of constructors. The constructor of a subclass will call the constructor of the parent class before calling its own constructor. If the parent class does not have a parameterless constructor, the subclass must explicitly call the parent class's constructor. for example:
public class Shape {
public Shape() {
System.out.println("Shape constructor");
}
}
public class Circle extends Shape {
public Circle() {
super(); // explicitly call the parent class constructor System.out.println("Circle constructor");
}
}
If you do not call super() explicitly, the compiler will automatically add a super() call without parameters, but if the parent class does not have a parameterless constructor, it will cause a compilation error. Another point to note is that Java does not support multiple inheritance, but can achieve the effect of multiple inheritance through interfaces. for example:
public interface Drawable {
void draw();
}
public interface Resizable {
void resize();
}
public class Circle extends Shape implements Drawable, Resizable {
@Override
public void draw() {
System.out.println("Drawing a circle");
}
@Override
public void resize() {
System.out.println("Resizing a circle");
}
}
In this way, the Circle class can implement both Drawable and Resizable interfaces at the same time, thereby achieving the effect of multiple inheritance. Finally, share some of my best practices when using inheritance. First of all, try to maintain a simple and obvious inheritance level and avoid excessively deep inheritance relationships. Secondly, try to use combination rather than inheritance to implement code reuse, which can reduce the degree of coupling between classes. Finally, pay attention to the dependencies between the parent class and the child class to ensure that the child class does not over-rely rely on the implementation details of the parent class. In general, the inheritance relationship and implementation methods of classes in Java are very flexible, but we also need to use them carefully in actual development to avoid increasing code complexity caused by abuse. I hope these sharing will be helpful to you. If you have other questions or experiences, please feel free to communicate!The above is the detailed content of What is the inheritance of the class in java? Analysis of the inheritance relationship and implementation method of the class. For more information, please follow other related articles on the PHP Chinese website!
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