Java学习——包及可见性

Posted 2021-01-12 蔡军帅

 

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
    }
}