Reading Guide
1. Case Study of Encapsulation of Student and Professional Information
2. New Demand Statistics Professionals
Case Study of Student and Professional Information Encapsulation
Subject class
package com.hala.modle;
public class Subject {
private String SubjectName;
private String SubjectNum;
private int SubjectLife;
public Subject(){
}
public Subject(String subjectName,String subjectNum,int subjectLife){
this.setSubjectName(subjectName);
this.setSubjectNum(subjectNum);
this.setSubjectLife(subjectLife);
}
public String getSubjectName() {
return SubjectName;
}
public void setSubjectName(String subjectName) {
SubjectName = subjectName;
}
public String getSubjectNum() {
return SubjectNum;
}
public void setSubjectNum(String subjectNum) {
SubjectNum = subjectNum;
}
public int getSubjectLife() {
return SubjectLife;
}
public void setSubjectLife(int subjectLife) {
if(subjectLife<=0)
return ;
else
SubjectLife = subjectLife;
}
public String info() {
String str = "Professional information is as follows:\n Professional Name:" + this.getSubjectName() + "\n Professional Number:" + this.getSubjectNum() + "\n Professional years:"
+ this.getSubjectLife();
return str;
}
}
Student class
package com.hala.modle;
public class Student {
private String num;
private String name;
private String sex;
private int age;
private Subject studentSubject;
public Subject getStudentSubject() {
if(this.studentSubject==null)
this.studentSubject=new Subject();
//The importance of parameterless construction is shown here
return studentSubject;
}
public void setStudentSubject(Subject studentSubject) {
this.studentSubject = studentSubject;
}
public Student() {
}
public Student(String num, String name, String sex, int age) {
this.setAge(age);
this.setName(name);
this.setNum(num);
this.setSex(sex);
}
public Student(String num, String name, String sex, int age,Subject studentSubject) {
this.setAge(age);
this.setName(name);
this.setNum(num);
this.setSex(sex);
this.setStudentSubject(studentSubject);
}
public String getNum() {
return num;
}
public void setNum(String num) {
this.num = num;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public int getAge() {
return age;
}
/**
*
* @param age Age
* Age > 0 and < 100
*
*/
public void setAge(int age) {
if(age<=0||age>=100)
age=18;
this.age = age;
}
/**
* Introduction of students
* @return Name, school number, gender, age
*/
public String introduction(){
String str = "The student information is as follows:\n Student Name:" + this.getName() + "\n Student ID:" + this.getNum() + "\n Student gender:"
+ this.getSex()+"\n Student age:"+this.getAge();
return str;
}
/**
* Introduction of students
* @param SubjectName
* @param SubjectLife
* @return Name, school number, gender, age, major, length of study
* Solution 1; What to Pass
*/
public String introduction(String SubjectName,String SubjectLife){
String str = "The student information is as follows:\n Student Name:" + this.getName() + "\n Student ID:" + this.getNum() + "\n Student gender:"
+ this.getSex()+"\n Student age:"+this.getAge()+"\n Major:"+SubjectName+"\n Years of study:"+SubjectLife;
return str;
}
/**
* Introduction of students
* @param mySubject
* @return Name, school number, gender, age, major, length of study, major number
* Solution 2; Pass Subject in as a method parameter
*/
public String introduction(Subject mySubject) {
String str = "The student information is as follows:\n Student Name:" + this.getName() + "\n Student ID:" + this.getNum() + "\n Student gender:" + this.getSex()
+ "\n Student age:" + this.getAge() + "\n Learning Specialties:" + mySubject.getSubjectName() + "\n Years of study:"
+ mySubject.getSubjectLife() + "\n Professional Number" + mySubject.getSubjectNum();
return str;
}
/**
* Introduction of students
* @return Name, school number, gender, age, major, length of study, major number
* Solution 3: Treat Subject as a property of Student
*/
public String introduction1s() {
String str = "The student information is as follows:\n Student Name:" + this.getName() + "\n Student ID:" + this.getNum() + "\n Student gender:" + this.getSex()
+ "\n Student age:" + this.getAge() + "\n Learning Specialties:" + this.getStudentSubject().getSubjectName() + "\n Years of study:"
+ this.getStudentSubject().getSubjectLife() + "\n Professional Number" + this.getStudentSubject().getSubjectNum();
return str;
}
}
SubjectTest class
package com.hala.test;
import com.hala.modle.*;
public class SubjectTest {
public static void main(String[] args) {
Subject sub1=new Subject("Computer Science and Application","J0001",4);
System.out.println(sub1.info());
}
}
StudentTest class
package com.hala.test;
import com.hala.modle.Student;
import com.hala.modle.Subject;
public class StudentTest {
public static void main(String[] args) {
Student stu1=new Student("s01","Zhang San","male",18);
System.out.println(stu1.introduction());
System.out.println("+++++++++++++++++++++++++++++++++");
Student stu2=new Student("s02","Li Si","female",19);
System.out.println(stu2.introduction("Computer Science and Technology", "4 year"));
System.out.println("+++++++++++++++++++++++++++++++++");
Subject sub1=new Subject("Computer Science and Application","J0001",4);
Student stu3=new Student("s03","King Five","female",18);
System.out.println(stu3.introduction(sub1));
System.out.println("+++++++++++++++++++++++++++++++++");
Student stu4=new Student("s04","Zhao Six","male",20,sub1);
System.out.println(stu4.introduction1s());
}
}
Output Results
The student information is as follows:
Student Name: Zhang San
Student number: s01
Student gender: male
Student age: 18
+++++++++++++++++++++++++++++++++
The student information is as follows:
Student Name: Li Si
Student number: s02
Student gender: female
Student age: 19
My major is computer science and technology
Years of study: 4 years
+++++++++++++++++++++++++++++++++
The student information is as follows:
Student Name: Wang Wu
Student number: s03
Student gender: female
Student age: 18
Learning Major: Computer Science and Application
Years of study: 4
Professional Number J0001
+++++++++++++++++++++++++++++++++
The student information is as follows:
Student Name: Zhao Six
Student number: s04
Student gender: male
Student age: 20
Learning Major: Computer Science and Application
Years of study: 4
Professional Number J0001
New Demand Statistics Professionals
Subject class
package com.hala.modle;
public class Subject {
private String SubjectName;
private String SubjectNum;
private int SubjectLife;
private int studentNum;
private Student[] myStudent;
public Subject(){
}
public Subject(String subjectName,String subjectNum,int subjectLife){
this.setSubjectName(subjectName);
this.setSubjectNum(subjectNum);
this.setSubjectLife(subjectLife);
}
public Subject(String subjectName,String subjectNum,int subjectLife,Student[] myStudent){
this.setSubjectName(subjectName);
this.setSubjectNum(subjectNum);
this.setSubjectLife(subjectLife);
this.setMyStudent(myStudent);
}
public String getSubjectName() {
return SubjectName;
}
public void setSubjectName(String subjectName) {
SubjectName = subjectName;
}
public String getSubjectNum() {
return SubjectNum;
}
public void setSubjectNum(String subjectNum) {
SubjectNum = subjectNum;
}
public int getSubjectLife() {
return SubjectLife;
}
public void setSubjectLife(int subjectLife) {
if(subjectLife<=0)
return ;
else
SubjectLife = subjectLife;
}
/**
* Get student information for the optional course. If the array holding the student information is not initialized, initialize the array with a length of 200 first
* @return Array holding student information
*/
public Student[] getMyStudent() {
if(this.myStudent==null)
this.myStudent=new Student[200];
//If this sentence is not set, null pointer exceptions are caused, and null pointer exceptions are often caused by uninstantiated objects
return myStudent;
}
public void setMyStudent(Student[] myStudent) {
this.myStudent = myStudent;
}
public int getStudentNum() {
return studentNum;
}
public void setStudentNum(int studentNum) {
this.studentNum = studentNum;
}
public String info() {
String str = "Professional information is as follows:\n Professional Name:" + this.getSubjectName() + "\n Professional Number:" + this.getSubjectNum() + "\n Professional years:"
+ this.getSubjectLife();
return str;
}
/**
* 1.Implement storing student information management in an array
* 2.Reset the number of students
* @param Student Information Management
*/
public void addStudent(Student stu){
for(int i=0;i<this.getMyStudent().length;i++){
if(this.getMyStudent()[i]==null){
stu.setStudentSubject(this);
//This indicates that referencing a data type as a parameter is equivalent to referencing
this.getMyStudent()[i]=stu;
//Two sentences in place in one step establish the connection from students to disciplines, and also from disciplines to students.
//The top one-step approach chooses the third solution to the problem
this.studentNum=i+1;
break;
}
}
}
}
Student class
package com.hala.modle;
public class Student {
private String num;
private String name;
private String sex;
private int age;
private Subject studentSubject;
public Subject getStudentSubject() {
if(this.studentSubject==null)
this.studentSubject=new Subject();
//The importance of parameterless construction is shown here
return studentSubject;
}
public void setStudentSubject(Subject studentSubject) {
this.studentSubject = studentSubject;
}
public Student() {
}
public Student(String num, String name, String sex, int age) {
this.setAge(age);
this.setName(name);
this.setNum(num);
this.setSex(sex);
}
public Student(String num, String name, String sex, int age,Subject studentSubject) {
this.setAge(age);
this.setName(name);
this.setNum(num);
this.setSex(sex);
this.setStudentSubject(studentSubject);
}
public String getNum() {
return num;
}
public void setNum(String num) {
this.num = num;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public int getAge() {
return age;
}
/**
*
* @param age Age
* Age > 0 and < 100
*
*/
public void setAge(int age) {
if(age<=0||age>=100)
age=18;
this.age = age;
}
/**
* Introduction of students
* @return Name, school number, gender, age
*/
public String introduction(){
String str = "The student information is as follows:\n Student Name:" + this.getName() + "\n Student ID:" + this.getNum() + "\n Student gender:"
+ this.getSex()+"\n Student age:"+this.getAge();
return str;
}
/**
* Introduction of students
* @param SubjectName
* @param SubjectLife
* @return Name, school number, gender, age, major, length of study
* Solution 1; What to Pass
*/
public String introduction(String SubjectName,String SubjectLife){
String str = "The student information is as follows:\n Student Name:" + this.getName() + "\n Student ID:" + this.getNum() + "\n Student gender:"
+ this.getSex()+"\n Student age:"+this.getAge()+"\n Major:"+SubjectName+"\n Years of study:"+SubjectLife;
return str;
}
/**
* Introduction of students
* @param mySubject
* @return Name, school number, gender, age, major, length of study, major number
* Solution 2; Pass Subject in as a method parameter
*/
public String introduction(Subject mySubject) {
String str = "The student information is as follows:\n Student Name:" + this.getName() + "\n Student ID:" + this.getNum() + "\n Student gender:" + this.getSex()
+ "\n Student age:" + this.getAge() + "\n Learning Specialties:" + mySubject.getSubjectName() + "\n Years of study:"
+ mySubject.getSubjectLife() + "\n Professional Number" + mySubject.getSubjectNum();
return str;
}
/**
* Introduction of students
* @return Name, school number, gender, age, major, length of study, major number
* Solution 3: Treat Subject as a property of Student
*/
public String introduction1s() {
String str = "The student information is as follows:\n Student Name:" + this.getName() + "\n Student ID:" + this.getNum() + "\n Student gender:" + this.getSex()
+ "\n Student age:" + this.getAge() + "\n Learning Specialties:" + this.getStudentSubject().getSubjectName() + "\n Years of study:"
+ this.getStudentSubject().getSubjectLife() + "\n Professional Number" + this.getStudentSubject().getSubjectNum();
return str;
}
}
SubjectTest class
package com.hala.test;
import com.hala.modle.*;
public class SubjectTest {
public static void main(String[] args) {
Subject sub1=new Subject("Computer Science and Application","J0001",4);
Student stu1=new Student("s01","Zhang San","male",18);
Student stu2=new Student("s02","Li Si","female",19);
Student stu3=new Student("s03","King Five","female",18);
Student stu4=new Student("s04","Zhao Six","male",20);
sub1.addStudent(stu1);
sub1.addStudent(stu2);
sub1.addStudent(stu3);
sub1.addStudent(stu4);
System.out.println(sub1.getStudentNum());
System.out.println(stu1.introduction1s());
//Because the Subject class is one step in place, you can output information about students and their disciplines.
}
}
Output Results
4
The student information is as follows:
Student Name: Zhang San
Student number: s01
Student gender: male
Student age: 18
Learning Major: Computer Science and Application
Years of study: 4
Professional Number J0001
Two ways to prevent null pointer exceptions 