Java:封装案例（续）

知识总结：

本题在之前的基础上增加案例：统计总共有多少学生报名

主要改造在subject.java中:

1.属性增加：

private Student[]myStudents;

privateintstudentNum;

2.构造方法增加：

//带4参构造：实现对学科名称、编号、学制年限、学生信息赋值

public Subject(Stringname, StringsubjectNo,intsubjectLife,Student[]myStudents) {

// this.subjectName=subjectName;

this.setSubjectName(name);// 安全起见

this.setSubjectNo(subjectNo);

this.setSubjectLife(subjectLife);

this.setMyStudents(myStudents);

}

3.方法增加：

getter/setter方法增加：

public Student[] getMyStudents() {

if(this.myStudents==null)//如果没有初始化，实例化开辟空间

{

this.myStudents=new Student[200];

}

returnmyStudents;

}

public void setMyStudents(Student[] myStudents) {

this.myStudents =myStudents;

}

    //学生个数

public int getStudentNum() {

returnstudentNum;

}

public void setStudentNum(int studentNum) {

this.studentNum =studentNum;

}

add方法增加：

public void addStudent(Studentstu)

{

/*

* 1,将学生保存在数组中

* 2，将学生个数保存到studentNum[]数组当中

*/

//1.

for(inti=0;i<this.getMyStudents().length;i++)

{

if(this.getMyStudents()[i]==null)//找到空地，插入学生

{

this.getMyStudents()[i]=stu;

//2.

this.studentNum=i+1;

return;

}

}

}

subject.java

package com.imooc.model;/** * 专业类 * @author zhang ziwei * */ public class Subject {// 成员属性：学科名称，学科编号，学制年限,报名选修的学生信息、报名选修的学生个数private String subjectName;private String subjectNo;private int subjectLife;private Student[] myStudents;private int studentNum;//无参构造public Subject() {}//带3参构造：实现对学科名称、编号、学制年限赋值public Subject(String name, String subjectNo, int subjectLife) {// this.subjectName=subjectName;this.setSubjectName(name);// 安全起见this.setSubjectNo(subjectNo);this.setSubjectLife(subjectLife);}//带4参构造：实现对学科名称、编号、学制年限、学生信息赋值public Subject(String name, String subjectNo, int subjectLife,Student[] myStudents) {// this.subjectName=subjectName;this.setSubjectName(name);// 安全起见this.setSubjectNo(subjectNo);this.setSubjectLife(subjectLife);this.setMyStudents(myStudents);}/** * 获取选修专业的学生信息的，如果保存的学生信息未被初始化，则先初始化长度200 * @return 保存学生信息的数组 */public Student[] getMyStudents() {if(this.myStudents==null)//如果没有初始化，实例化开辟空间{this.myStudents=new Student[200];}return myStudents;}public void setMyStudents(Student[] myStudents) {this.myStudents = myStudents;}    //学生个数public int getStudentNum() {return studentNum;}public void setStudentNum(int studentNum) {this.studentNum = studentNum;}// 名称public void setSubjectName(String subjectName) {this.subjectName = subjectName;}public String getSubjectName() {return this.subjectName;}// 科目public String getSubjectNo() {return subjectNo;}public void setSubjectNo(String subjectNo) {this.subjectNo = subjectNo;}// 学制年限public int getSubjectLife() {return subjectLife;}public void setSubjectLife(int subjectLife) {if (subjectLife <= 0) {return;}this.subjectLife = subjectLife;}/** * 专业介绍的方法 *  * @return 专业介绍的相关信息，包括名称、编号、年限 */public String info() {String str = "专业信息如下：\n专业名称：" + this.getSubjectName() + "\n专业编号：" + this.getSubjectNo() + "\n学制年限："+ this.getSubjectLife();// 对于很长的字符串打印可以用command+shift+f（ctrl+shift+f）格式化使得格式更好看return str;}public void addStudent(Student stu){/* * 1,将学生保存在数组中 * 2，将学生个数保存到studentNum[]数组当中 *///1.for(int i=0;i<this.getMyStudents().length;i++){if(this.getMyStudents()[i]==null)//找到空地，插入学生{this.getMyStudents()[i]=stu;//2.this.studentNum=i+1;return;}}} }

Student.java:

package com.imooc.model;public class Student {// 成员属性：学号，姓名，性别，年龄private String student_id;private String student_name;private String student_sex;private int student_age;//实现关联学生，学科关联的，解决方法3:将专业信息作为成员属性存在private Subject student_subject;//注意，类型是一个对象// 无参数构造public Student() {super();}// 4参构造，实现对学号，姓名，年龄赋值，创建对象的赋值public Student(String student_id, String student_name, String student_sex, int student_age,Subject student_subject) {this.setStudent_id(student_id);this.setStudent_name(student_name);this.setStudent_sex(student_sex);this.setStudent_age(student_age);this.setStudent_subject(student_subject);}//3参构造,实现对学号，姓名，年龄赋值public Student(String student_id, String student_name, String student_sex, int student_age) {this.setStudent_id(student_id);this.setStudent_name(student_name);this.setStudent_sex(student_sex);this.setStudent_age(student_age);}// getter/setter接口public String getStudent_id() {return student_id;}public void setStudent_id(String student_id) {this.student_id = student_id;}public String getStudent_name() {return student_name;}public void setStudent_name(String student_name) {this.student_name = student_name;}public String getStudent_sex() {return student_sex;}public void setStudent_sex(String student_sex) {// 限制性别只能是男或者女，反之我们强制性男if (student_sex.equals("男") | student_sex.equals("女")) // 也可以写成(student_sex="男"student_sex="女"){this.student_sex = student_sex;} elsethis.student_sex = "男";}public int getStudent_age() {return student_age;}public void setStudent_age(int student_age) {if (student_age <= 60 & student_age >= 10) {this.student_age = student_age;} elsethis.student_age = 18;// 强制赋值}/** * 获取专业对象，如果没有实例化，先实例化再返回 * @return 专业对象信息 */public Subject getStudent_subject(){ if(this.student_subject==null)//防止getStudent_subject()是没有实例化的{this.student_subject=new Subject();//无参构造的重要性体现出来}return student_subject;}public void setStudent_subject(Subject student_subject) {this.student_subject = student_subject;}/**无参 * 学生自我介绍 *  * @return 自我介绍的信息，包括姓名，学号，性别，年龄 */public String introduction() {String str = "学生信息如下：\n姓名:" + this.getStudent_name() + "\n学号：" + this.getStudent_id() + "\n性别："+ this.getStudent_sex() + "\n年龄：" + this.getStudent_age()+"\n所报专业名称：" + this.getStudent_subject().getSubjectName() + "\n学制年限："+ this.getStudent_subject().getSubjectLife();//！！尤其注意这种表示先调用对象，再通过对象调用方法return str;}/**解决方法1:参数传参 * 学生自我方法介绍，实现学生学科相关联 * @param subject_name * @param subject_life * @return 自我介绍的信息，包括姓名，学号，性别，年龄，所学专业名称，学制年限 */public String introduction(String subject_name, int subject_life) {String str = "学生信息如下：\n姓名:" + this.getStudent_name() + "\n学号：" + this.getStudent_id() + "\n性别："+ this.getStudent_sex() + "\n年龄：" + this.getStudent_age() + "\n所报专业名称：" + subject_name + "\n学制年限："+ subject_life;return str;}/**解决方法2:对象传参 * 学生自我方法介绍，实现学生学科相关联 * @param mySubject(构建了一个对象) * @return自我介绍的信息，包括姓名，学号，性别，年龄，所学专业名称，学制年限 */public String introduction(Subject mySubject){String str = "学生信息如下：\n姓名:" + this.getStudent_name() + "\n学号：" + this.getStudent_id() + "\n性别："+ this.getStudent_sex() + "\n年龄：" + this.getStudent_age() + "\n所报专业名称：" + mySubject.getSubjectName() + "\n学制年限："+ mySubject.getSubjectLife();return str;}}

SchoolTest.java:

package com.imooc.test;import com.imooc.model.*;//导入所有类public class SchoolTest {public static void main(String[] args) {//测试subject类Subject sub1=new Subject("计算机科学与应用","J0001",4);System.out.println(sub1.info());        System.out.println("=====================================");                //测试学生        Student stu1=new Student("cs6518822","刘华华","女",20);        System.out.println(stu1.introduction());                System.out.println("=====================================");                //测试关联学生1，方法中传入参数        Student stu2=new Student("cs6518732","张子蔚","男",17);        System.out.println(stu2.introduction("计算机科学与应用",4));        System.out.println("=====================================");                //测试关联学生2，方法中传入对象        Student stu3=new Student("cs6518797","胡京督","男",21);        System.out.println(stu3.introduction(sub1));        System.out.println("=====================================");                //测试关联学生3,构造方法中传入对象        Student stu4=new Student("cs6518779","刘凯瑞","男",20,sub1);        System.out.println(stu4.introduction());        System.out.println("=====================================");                //测试指定专业的中到底有多少学生报名        sub1.addStudent(stu1);        sub1.addStudent(stu2);        sub1.addStudent(stu3);        sub1.addStudent(stu4);        System.out.println("计算机科学与应用的专业中已有："+sub1.getStudentNum()+"学生进行报名");}}

执行情况：（最后一排显示报名总数）