1.在同一个类中：创建的对象，不管成员的可见修饰符可以直接调用。

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.在同一个包中不同类中的可见性：私有不可见，其它都可见

//程序名为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;

    }

//程序名为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：先注意类的可见性，可见后只有public成员可见

//程序名为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;

    }

//程序名为 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;

    }

}

//程序名为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();//注意是否可行

    }

}