Application of protected access modifier for Java functions

Answer: The protected access modifier allows subclasses and classes in the same package to access the member, while blocking access to classes in other packages. Detailed Description: Protected members are accessible in the defining class, subclasses, and other classes in the same package. Classes in different packages cannot access protected members. Applicable to: a) Allow subclasses to access parent class members. b) Access within the package is allowed, but access outside the package is blocked. For example, the protected method getSpeed() of the parent class Vehicle can be accessed by the subclass Car, but not by the class Truck that is not in the same package.

Java function access modifier: protected

Introduction

In In Java, protected is an access modifier used to specify restricted access levels for methods, fields, and constructors. It is more restrictive than public but has looser access than default.

Semantics

• protected Members can be accessed in the class in which they are defined, in subclasses, and in other classes in the same package .
• For classes in different packages, protected members cannot be accessed.

Application

protected Access permission modifiers are often used in the following situations:

• When you want a child When a class can access members of the parent class but prevents other classes from accessing them.
• When you want to provide access to members within a package, but prevent access outside the package.

Practical case

Consider a parent classVehicle, which has a protected methodgetSpeed (). The

public abstract class Vehicle {
    protected int speed;

    public void getSpeed() {
        // ...
    }
}

Car class is a subclass of Vehicle and it has access to the getSpeed() method because it inherits from Vehicle.

public class Car extends Vehicle {
    public void displaySpeed() {
        // 可以访问父类的 protected 方法
        getSpeed();
    }
}

However, the Truck class is not in the same package as the Vehicle, so it cannot access the getSpeed() method.

// Truck 类在一个不同的包中
public class Truck {
    // 无法访问 Vehicle 中的 protected 方法
    // getSpeed();
}

Conclusion

protected Access modifiers provide a way to restrict access to class members while allowing subclasses and those in the same package access by other classes. It is useful when designing classes with inheritance relationships and restricting access rights in specific packages.

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