Java_32_클래스 객체 배열

 

        
 - 데이터가 많을 경우 각각 객체를 선언하지 않고 배열을 활용합니다.

    - 클래스/객체 배열
     1. 객체의 개수를 정의합니다.
2. 각 개체를 생성합니다.
- 생성자를 통해 객체를 생성해야 합니다.

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package oop.basic; //모든 클래스는 패키지 안에 생성합니다.   public class StudentApp {     // 모든 함수_메소드는 클래스 안에 작성합니다.          // 별칭을 지정합니다.     static void printInfo(Student student) {                 /*             - Scope 내의 코드에 대해 별칭을 지정하여 실행할 수 있습니다.                 '별칭' {                     별칭으로 지정할 코드                 }             - 문제                 - 외부에서 Scope 내의 변수에 접근할 수 없습니다.             >>> 별칭은 내부 변수를 초기화 하는 매개 변수_()를 제공합니다.                         - 매개 변수 이름은 내부 변수 이름과 동일하게 작성합니다.                 '별칭'('매개 변수 이름') {                     별칭으로 지정할 코드                 }             >>> Compile 하기 위해 매개 변수의 데이터 타입을 알려주어야 합니다.                 '별칭'('데이터 타입' '매개 변수 이름') {                     별칭으로 지정할 코드                 }             >>> 반환할 데이터 타입을 지정해주어야 합니다.                 void '별칭'('데이터 타입' '매개 변수 이름') {                     별칭으로 지정할 코드                 }             >>> static을 통해 클래스 이름을 통해 객체를 생성하지 않고도 접근이 가능합니다.                 static void '별칭'('데이터 타입' '매개 변수 이름') {                     별칭으로 지정할 코드                 }          */         System.out.println("printInfo : " + student.studentName);     }          public static void main(String[] args) {         // Java의 모든 코드는 함수 안에 작성합니다.         /*             - 'Student.java'에서 작성한 Student 클래스를 사용하기                 1) 클래스 spec을 만족하는 객체를 생성합니다.                 2) 데이터 저장          */                  Student student1 = new Student();                 /*                  - 복합형 데이터를 다루는 클래스이기 때문에 new 로 객체를 생성합니다.                 - 대입 연산자의 왼쪽 부터 실행됩니다.                     - Heap 공간에 Student() 메소드의 객체를 생성합니다.                         - 클래스의 spec의 조건을 충족시키는지 확인합니다.                     - Stack 공간에 Heap 공간의 Student() 메소드의 메모리의 주소를                          student1 변수에 저장합니다.              */                  // 데이터 저장         student1.studentName = "stName1";         student1.address = "Address 123-123";             /*                 - 클래스의 spec에 맞는 객체의 정보를 저장합니다.                     '클래스 이름'.'멤버 변수 이름' = '저장할 값';              */                  // 데이터 출력         student1.showStudentInfo();             /*                 Name : stName1                 Address : Address 123-123                     - showStudentInfo() 함수를 호출하여 실행합니다.                         - 함수를 작성한 페이지에 가지 않는 한 함수의 자세한 내용을 알 수 없습니다.              */                  System.out.println(student1.studentName);                  Student student2 = new Student();    // 새로운 메소드 객체를 생성합니다.         student2.studentName = "stName2";         student2.showStudentInfo();             /*                 Name : stName2                 Address : null                     - student2 객체와 student1 객체는 다른 객체이므로 다른 정보가 출력됩니다.                     - student2 객체에 address 정보를 저장하지 않았으므로 null 값이 출력됩니다.              */         System.out.println();         printInfo(student2);             /*                 printInfo : stName1              */                  // 멤버 변수 접근         Student student3 = new Student();         student3.setStudentName("stName3");                // 값을 저장합니다.         System.out.println();         System.out.println("student3.getStudentName() : " + student3.getStudentName());                     // 값을 불러옵니다.         System.out.println("student3.studentName : " + student3.studentName);                         // 값을 출력합니다.             /*                 student3.getStudentName() : stName3                 student3.studentName : stName3              */           // 멤버 변수 접근 제한         /*         student3.grade();             - 오류 : The method grade() is undefined for the type Student             - Student 클래스에서 private으로 선언한 grade의 값에 접근할 수 없습니다.          */         System.out.println();         System.out.println("student3.getGrade() : " + student3.getGrade());             /*                 student3.getGrade() : 0              */           student3.setGrade(7);         System.out.println();         System.out.println("student3.setGrade(7) : " + student3.getGrade());             /*                 student3.setGrade(7) : 7              */                  // 생성자         Student student4 = new Student(1);         student4.setStudentName("stName4");         student4.setGrade(2);         student4.showStudentInfo();             /*                 Name : stName4                 Address : null                 ID : 1              */                  Student student5 = new Student("stName5");         student5.showStudentInfo();             /*                 Name : stName5                 Address : null                 ID : 0              */                  Student student6 = new Student(2,"stName6","Address 456-456",2);         student6.showStudentInfo();             /*                 Name : stName6                 Address : Address 456-456                 ID : 2              */                  // 객체 배열         Student students[] = {                 student6,                  new Student(3, "stName7", "Address 789-789", 1),                 new Student("stName8")                         // 이름 데이터만 넘겨주는 생성자가 존재하므로 가능합니다.         };                  for(int i=0; i<3; i++) {    // 출력             students[i].showStudentInfo();;         }             /*                 Name : stName6                 Address : Address 456-456                 ID : 2                 Name : stName7                 Address : Address 789-789                 ID : 3                 Name : stName8                 Address : null                 ID : 0              */                  // 대량 데이터 등록/출력         Student stu[] = new Student[100];         for (int i=1; i<=100; i++) {        // 데이터 저장             stu[i-1] = new Student(i, "stName "+i, "Address"+i, 2);         }         for (int i=1; i<=100; i++) {        // 데이터 출력             System.out.println(i + "\t" + stu[i-1].studentName + "\t"                                      + stu[i-1].address + "\t" + stu[i-1].getGrade());         }             /*                 1    stName 1    Address1    2                 2    stName 2    Address2    2                 3    stName 3    Address3    2                 ...                 100    stName 100    Address100    2              */     } }

 - 세 명의 이름과 전화번호 관리하기
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import java.util.*;   class Member {     // 클래스 생성     String name;     // 이름 객체 생성     String tel;     // 번호 객체 생성     Member(String name, String tel) {         // 이름과 번호 객체를 가지는 생성자 생성         this.name = name;         this.tel = tel;     }       void disp() {         // 출력 생성자 생성         System.out.println(name + "\'s phone number : " + tel);     } }   public class same {     public static void main(String[] args) {         Scanner in = new Scanner(System.in);         Member[] mb = new Member[3];         // 클래스 배열 생성 _ 객체의 개수 지정         for (int i = 0; i < 3; ++i) {             // 각 객체 생성하기 위함             //              System.out.print("Input name:");             String name = in.next();             System.out.print("Input tel: ");             String tel = in.next();             mb[i] = new Member(name, tel);             // 각각의 객체를 생성자를 이용하여 생성하는 곳         }           for (int i = 0; i < 3; ++i) {             mb[i].disp();         }     } }

 - 인원수를 입력받아 그 인원수 만큼 이름, 국어, 영어점수를 입력받아 이름, 총점, 순위를 출력
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import java.util.*;   class Member {     String name;     int kor, eng;     // 성적 변수     int tot;     // 총점     int lank = 1;     // 랭킹       Member(String name, int kor, int eng) {         // 생성자 서언         this.name = name;         this.kor = kor;         this.eng = eng;         this.tot = kor + eng;     }       void disp() {         // 출력         System.out.println(name + "'s total score : " + tot + " | lank : " + lank);     } }   public class same {     public static void main(String[] args) {         Scanner in = new Scanner(System.in);         // 입력 기능         System.out.print("Input people count: ");         int people = in.nextInt();         // 인원수 입력 받기          Member[] mb = new Member[people];    // 객체 선언부         // 입력받은 인원수 크기의 배열 생성           for (int i = 0; i < people; i++) {             // 인원 수 만큼 입력 받기             System.out.print("Input name: ");             String name = in.next();             System.out.printf("Input %s's kor: ", name);             int kor = in.nextInt();             System.out.printf("Input %s's eng: ", name);             int eng = in.nextInt();             mb[i] = new Member(name, kor, eng);    // 객체 생성부         }           for (int i = 0; i < people; ++i) {             // i = 내 성적             for (int j = 0; j < people; ++j) {                 // j = 다른 학생 성적                 if (mb[i].tot < mb[j].tot) {                     // 내 성적이 다른 학생 성적의 총 점보다 작으면                     mb[i].lank++;                     // 내 순위를 하나 올린다.                 }             }         }           for (int i = 0; i < people; ++i) {             mb[i].disp();         }     } }