1.在同一個類中：創建的對象，不管成員的可見修飾符可以直接調用。
package studentpackage;
public class Student {
    public long id;
    protected String name;
    private char sex;
    int age;

    public String toString() {
        return id + name + sex + age;
    }

    public static void main(String args[]) {
        Student s1 
 
= new Student();
        s1.id = 20110010l;
        s1.name = "zhangshan";
        s1.sex = ‘M‘;
        s1.age = 20;
        System.out.println(s1);
    }
}
2.在同一個包中不同類中的可見性：私有不可見，其它都可見
//程序名為Student.java
package studentpackage;
public class Student {
    public long id;
    protected String name;
    
 
private char sex;
    int age;

    public String toString() {
        return id + name + sex + age;
    }

//程序名為TestStudent.java
package studentpackage;
public class TestStudent {
    public static void main(String[] args) {
        Student s1=new Student();
        s1.id = 20110010l;
        s1.name 
 
= "zhangshan";
        s1.sex = ‘M‘;
        s1.age = 20;
        System.out.println(s1);
    }
}

3．在不同的包中：先註意類的可見性，可見後只有public成員可見
//程序名為Student.java
package studentpackage;
public class Student {
    public long id;
    protected String name;
    private char sex;
    int age;

    public String toString() {
        return id + name + sex + age;
    }

//程序名為 XueYuan.java
package studentpackage;
class XueYuan {
    Long xyid;
    String xyName;
    String xyweizhi;
    public XueYuan() {
    }

    public XueYuan(Long xyid, String xyName, String xyweizhi) {
        super();
        this.xyid = xyid;
        this.xyName = xyName;
        this.xyweizhi = xyweizhi;
    }

    public String toString() {
        return xyid + xyName + xyweizhi;
    }
}

//程序名為TestStudent_xueyuan.java
package teststudentpackage;
import studentpackage.*;
public class TestStudent_xueyuan {
    public static void main(String[] args) {
        Student s1=new Student();
        s1.id = 20110010l;
        s1.name = "zhangshan";
        s1.sex = ‘M‘;
        s1.age = 20;
        System.out.println(s1);
        XueYuan xy1=new XueYuan();//註意是否可行
    }
}

Java學習——包及可見性