[JAVA] 상속

강의 

1. https://www.youtube.com/watch?v=iYW83DF6MHk&index=16&list=PLRx0vPvlEmdBjfCADjCc41aD4G0bmdl4R

java수업 때 A+을 맞았었다

하지만 인턴 면접 중 자바 A+이신데 클래스가 뭐죠? 상속이 뭐죠?

...? 들어보긴 했는데..하하..

나는 c++을 사용하고 java를 해봤으면서도 개념정립이 제대로 되어있지 않은것이다.

c++은 알고리즘을 풀기 위해서만 사용했고

java는 오직 좋은 점수를 받기 위해서 일회성 지식으로 가지고있었던 것이다.

그래서 개념을 새로 정립하려한다

class와 상속이 뭘까?

Person.java

public class Person { private String name; private int age; private int height; private int weight; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public int getHeight() { return height; } public void setHeight(int height) { this.height = height; } public int getWeight() { return weight; } public void setWeight(int weight) { this.weight = weight; } public Person(String name, int age, int height, int weight) { super();//부모 클래스의 생성자를 실행하겠다. this.name = name; this.age = age; this.height = height; this.weight = weight; } }

Student.java

public class Student extends Person { private String studentID; private int grade; private double GPA; public String getStudentID() { return studentID; } public void setStudentID(String studentID) { this.studentID = studentID; } public int getGrade() { return grade; } public void setGrade(int grade) { this.grade = grade; } public double getGPA() { return GPA; } public void setGPA(double gPA) { GPA = gPA; } //person이라는 것을 상속 받았기 때문에 자동으로 name age height가 나오게됨 public Student(String name, int age, int height, int weight, String studentID, int grade, double gPA) { super(name, age, height, weight); //상속하는 class 생성자 실행 this.studentID = studentID; this.grade = grade; GPA = gPA; } public void show(){ System.out.println("-----------------"); System.out.println("이름 : "+getName()); System.out.println("나이 : "+getAge()); System.out.println("키 : "+getHeight()); System.out.println("몸무게 : "+getWeight()); System.out.println("학년 : "+getGrade()); System.out.println("학점 : "+getGPA()); } }

Main.java

public class Main { public static void main(String[] args) { Student student1 = new Student("홍길동",20,175,2,"20170101",1,4.5); Student student2 = new Student("조규환",20,175,2,"20170101",1,4.5); student1.show(); student2.show(); } }

상속은 보통 붕어빵으로 비유한다 여기의 예제에서는 Person으로 비유했다

먼저 인간이 가지는 특성을 함수로 만들어놓고 Student는 Person을 상속받아서 사용한다.

Main은 Student를 불러오고 각각에 맞는 Constructor를 생성한다

그 이후 출력을 해주면 완벽하게 완성된다!

2. https://www.youtube.com/watch?v=5uFdYN_AiUY&index=17&list=PLRx0vPvlEmdBjfCADjCc41aD4G0bmdl4R

Main.java

import java.util.Scanner; public class Main { public static void main(String[] args) { Student student1 = new Student("홍길동",20,175,2,"20170101",1,4.5); Student student2 = new Student("조규환",20,175,2,"20170101",1,4.5); student1.show(); student2.show(); Teacher teacher1 = new Teacher("김선생",20,175,2,"20170101",1,4); teacher1.show(); Student[] students = new Student[100]; for(int j=0;j<100;j++) { students[j] = new Student("홍길동",20,175,70,j+"",1,4.5); } System.out.println("please enter the number of Students"); Scanner scan = new Scanner(System.in); int number = scan.nextInt(); Student[] students_new = new Student[number]; for(int j=0;j<number;j++) { String Student_ID = scan.next(); int age = scan.nextInt(); } } }

Person.java

public class Person { private String name; private int age; private int height; private int weight; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public int getHeight() { return height; } public void setHeight(int height) { this.height = height; } public int getWeight() { return weight; } public void setWeight(int weight) { this.weight = weight; } public Person(String name, int age, int height, int weight) { super();//부모 클래스의 생성자를 실행하겠다. this.name = name; this.age = age; this.height = height; this.weight = weight; } }

Student.java

public class Student extends Person { private String studentID; private int grade; private double GPA; public String getStudentID() { return studentID; } public void setStudentID(String studentID) { this.studentID = studentID; } public int getGrade() { return grade; } public void setGrade(int grade) { this.grade = grade; } public double getGPA() { return GPA; } public void setGPA(double gPA) { GPA = gPA; } //person이라는 것을 상속 받았기 때문에 자동으로 name age height가 나오게됨 public Student(String name, int age, int height, int weight, String studentID, int grade, double gPA) { super(name, age, height, weight); //상속하는 class 생성자 실행 this.studentID = studentID; this.grade = grade; GPA = gPA; } public void show(){ System.out.println("-----------------"); System.out.println("이름 : "+getName()); System.out.println("나이 : "+getAge()); System.out.println("키 : "+getHeight()); System.out.println("몸무게 : "+getWeight()); System.out.println("학년 : "+getGrade()); System.out.println("학점 : "+getGPA()); } }

Teacher.java

public class Teacher extends Person{ private String teacherID; private int monthSalary; private int workedYear; public String getTeacherID() { return teacherID; } public void setTeacherID(String teacherID) { this.teacherID = teacherID; } public int getMonthSalary() { return monthSalary; } public void setMonthSalary(int monthSalary) { this.monthSalary = monthSalary; } public int getWorkedYear() { return workedYear; } public void setWorkedYear(int workedYear) { this.workedYear = workedYear; } public Teacher(String name, int age, int height, int weight, String teacherID, int monthSalary, int workedYear) { super(name, age, height, weight); this.teacherID = teacherID; this.monthSalary = monthSalary; this.workedYear = workedYear; } public void show(){ System.out.println("-----------------"); System.out.println("이름 : "+getName()); System.out.println("나이 : "+getAge()); System.out.println("키 : "+getHeight()); System.out.println("몸무게 : "+getWeight()); System.out.println("선생님 ID : "+getTeacherID()); System.out.println("월급 : "+getMonthSalary()); System.out.println("일한 년도 : "+getWorkedYear()); } }

+) Getter Setter Constructor는 Source에서 자동으로 생성해주는 것을 이용하자!