How to solve Java method not implemented exception (MethodNotImplementedException)

How to solve the Java method not implemented exception (MethodNotImplementedException)

In Java development, sometimes you will encounter the method not implemented exception (MethodNotImplementedException), which is a common mistake. This exception is thrown when we declare an abstract method or a method in an interface but do not implement the method in its concrete implementation class. This article will explain how to resolve Java method not implemented exception and provide some code examples to aid understanding.

The most common way to resolve Java method not implemented exception is by implementing the missing method. We can create a new class to implement abstract methods or missing methods in the interface. The following is a sample code:

public interface Animal {
    void eat();
    void sleep();
}

public class Cat implements Animal {
    @Override
    public void eat() {
        System.out.println("Cat is eating");
    }
    
    @Override
    public void sleep() {
        System.out.println("Cat is sleeping");
    }
}

public class Dog implements Animal {
    @Override
    public void eat() {
        System.out.println("Dog is eating");
    }
    
    @Override
    public void sleep() {
        System.out.println("Dog is sleeping");
    }
    
    public void bark() {
        System.out.println("Dog is barking");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal cat = new Cat();
        cat.eat();
        cat.sleep();
        
        Animal dog = new Dog();
        dog.eat();
        dog.sleep();
        
        // dog.bark(); // 编译错误，Animal接口中没有定义bark()方法
    }
}

In the above example, we define an Animal interface, which contains eat() and sleep( )Two methods. Then we created two concrete classes Cat and Dog, which implemented the Animal interface respectively, and implemented eat() and sleep() method. Note that the Dog class also has an additional method bark(). This method is not a method in the Animal interface, so use AnimalA compilation error will occur when calling this method.

By implementing the missing method, we successfully avoided the method not implemented exception. When using concrete classes, we can call the implemented methods normally.

Another common solution is to implement some methods by creating an abstract class. This method is suitable for situations where we only need to implement some methods, while other methods can be implemented by subclasses. The following is a sample code:

public abstract class Shape {
    public abstract double calculateArea();
    
    public double calculatePerimeter() {
        return 0;
    }
}

public class Circle extends Shape {
    private double radius;
    
    public Circle(double radius) {
        this.radius = radius;
    }
    
    @Override
    public double calculateArea() {
        return Math.PI * radius * radius;
    }
    
    @Override
    public double calculatePerimeter() {
        return 2 * Math.PI * radius;
    }
}

public class Rectangle extends Shape {
    private double width;
    private double height;
    
    public Rectangle(double width, double height) {
        this.width = width;
        this.height = height;
    }
    
    @Override
    public double calculateArea() {
        return width * height;
    }
}

In the above example, we define an abstract class Shape, which contains the abstract method calculateArea() and the concrete method calculatePerimeter(). Then we created two concrete classes Circle and Rectangle, which respectively inherited the Shape class and implemented the calculateArea() method. The Circle class also overrides the calculatePerimeter() method.

By creating an abstract class, we can hand over the implementation of certain methods to subclasses to avoid the problem of unimplemented exceptions.

To sum up, there are two main ways to solve Java method unimplemented exceptions: by implementing missing methods or by creating abstract classes to implement some methods. Which method to choose depends on the specific needs, and we can choose the most suitable solution based on the actual situation.

I hope this article can help you solve the problem of unimplemented exceptions in Java methods and make your code more robust and maintainable.

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