Java中成员变量，成员方法作用域（private,protected,public,default）

• 测试文件目录结构
• private
• protected
• public
• default
• 总结

环境：JDK11

• 同一类中

package a;

public class Student {
    private int a = 3;

    public int getA() {
        return a;
    }

    public void setA(int a) {
        this.a = a;
    }
}

• 子类

package a;

public class Student_son extends Student{
    public int getStudent_a(){
        return a;
    }
}

• 同一包不同类

package a;

public class Main {
    public static void main(String[] args) {
        Student student = new Student();
        int student_a = student.a;
    }
}

• 其他包

package b;

import a.Student;

public class Person {
    public static void getStudent_a(){
        Student student = new Student();
        System.out.println(student.a);
    }
}

小结：private只能在类中访问

• 同一类中

package a;

public class Student {
    protected int a = 3;

    public int getA() {
        return a;
    }

    public void setA(int a) {
        this.a = a;
    }
}

同一类中可以访问

• 同一包下子类

package a;

public class Student_son extends Student{
    public int getStudent_a(){
        return a;
    }
}

子类中可以访问

• 不同包下子类

package b;

import a.Student;

public class Student_son2 extends Student {
    public int getStudent_a(){
        return a;
    }
}

不同包下子类可以访问

• 同一包不同类

package a;

public class Main {
    public static void main(String[] args) {
        Student student = new Student();
        int student_a = student.a;
    }
}

同一包不同类可以访问

• 其他包

package b;

import a.Student;

public class Person {
    public static void getStudent_a(){
        Student student = new Student();
        System.out.println(student.a);
    }
}

不同包下不可访问

小结：protected可在同一包下访问，或子类（可在不同包中）中访问

• 同一类中

package a;

public class Student {
    public int a = 3;

    public int getA() {
        return a;
    }

    public void setA(int a) {
        this.a = a;
    }
}

• 子类

package a;

public class Student_son extends Student{
    public int getStudent_a(){
        return a;
    }
}

• 同一包不同类

package a;

public class Main {
    public static void main(String[] args) {
        Student student = new Student();
        int student_a = student.a;
    }
}

• 其他包

package b;

import a.Student;

public class Person {
    public static void getStudent_a(){
        Student student = new Student();
        System.out.println(student.a);
    }
}

小结：public可在任何地方中访问

• 同一类中

package a;

public class Student {
    int a = 3;

    public int getA() {
        return a;
    }

    public void setA(int a) {
        this.a = a;
    }
}

• 同一包下子类

package a;

public class Student_son extends Student{
    public int getStudent_a(){
        return a;
    }
}

• 不同包下子类

package b;

import a.Student;

public class Student_son2 extends Student {
    public int getStudent_a(){
        return a;
    }
}

不同包下子类不能访问

• 同一包不同类

package a;

public class Main {
    public static void main(String[] args) {
        Student student = new Student();
        int student_a = student.a;
    }
}

• 其他包

package b;

import a.Student;

public class Student_son2 extends Student {
    public int getStudent_a(){
        return a;
    }
}

其他包不可访问

小结：default只能在同一包下访问

作用域范围：public>protected>default>private
Notes:protected 同一包或者子类（可以不同包）可以访问，default只能同一包下（可以不为子类）访问