What are the access permission modifiers in Java language?

1. Private permissions (private)

Private can modify data members, constructors, method members, but cannot modify classes (here refers to external classes, internal classes are not considered). Members modified by private can only be used in the class in which they are defined and cannot be called in other classes.

2. Default permissions (default)

Classes, data members, constructors, and method members can all use default permissions, that is, do not write any keywords. The default permission is the same package permission. Elements with the same package permission can only be called in the class in which they are defined and in classes in the same package.

3. Protected permissions (protected)

protected can modify data members, constructors, method members, but cannot modify classes (here refers to external classes, internal classes are not considered). Members modified by protected can be called in the class in which they are defined and in classes in the same package. If there are classes in different packages that want to call them, then this class must be a subclass of the class that defines them.

4. Public permissions (public)

public can modify classes, data members, constructors, and method members. Members modified by public can be called in any class, regardless of the same package or different packages, and are a modifier of maximum permissions.

Regarding the modifiers of the Java language, the following issues need to be noted:

1. Not every modifier can modify a class (referring to an external class), only public and default Can.

2. All modifiers can modify data members, method members, and constructors.

3. For the sake of code security, do not try to use modifiers with high permissions, but just apply them. For example, if there are no special needs for data members, use private as much as possible.

4. The modifier modifies the "accessed" permission.

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