JAVA 사용자 정의 데이터 타입 연습문제

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public class Student {
	int kor;
	int eng;
	int math;
	int sum;
	double avg;
	String name;
	int rank;
}

public static void main(String[] args) {
	Student[] students = new Student[10]; //학생 10명의 정보 저장할수 있는 배열 생성- Student 참조형타입
		
	for(int i = 0; i < students.length; i++){
		Student student = new Student(); //객체 생성
		//위 식이 for문 밖에 있으면, 학생을 1명 만들고  정보를 10번 바꾸는것
			
		student.name = "학생" + (i + 1);
		student.rank = 1;
		student.kor = (int)(Math.random() * 101);
		student.eng = (int)(Math.random() * 101);
		student.math = (int)(Math.random() * 101);
			
		students[i] = student;
	}
	//for문이 끝나면  10명의 학생의 정보가 students 배열에 저장되어 있다.

	//점수 합계, 평균 
	for(int i = 0; i < students.length; i++){
		students[i].sum = students[i].kor + students[i].eng + students[i].math;	
		students[i].avg = Math.round((double)students[i].sum / 3.0 * 100) / 100.0;
	}
		
	//석차
	for(int i = 0; i < students.length; i++){
		for(int j = 0; j < students.length; j++){
			if(students[i].sum < students[j].sum){
				students[i].rank++;
			}
		}
	}
		
	//정렬
	for(int i = 0; i < students.length-1; i++){
		int max = i;
		for(int j = i+1; j < students.length; j++){
			if(students[max].sum < students[j].sum){
				max = j;			
			}
		}
		Student temp = students[i];
		students[i] = students[max];
		students[max] = temp;
	}
		
	//출력
	System.out.println("\t국어\t영어\t수학\t합계\t평균\t석차");
	for(int i = 0; i < students.length; i++){
		System.out.println(students[i].name + "\t" + students[i].kor + "\t" + students[i].eng + "\t" + students[i].math + "\t" + students[i].sum + "\t" + students[i].avg + "\t" + students[i].rank);
	}
		
	//과목합계, 과목평균 출력
	int kor_sum = 0;
	int eng_sum = 0;
	int math_sum = 0;
	for(int i = 0; i < 3; i++){
		kor_sum += students[i].kor;
		eng_sum += students[i].eng;
		math_sum += students[i].math;
	}
	double kor_avg = Math.round((double)kor_sum / students.length * 100) / 100.0; 
	double eng_avg = Math.round((double)eng_sum / students.length * 100) / 100.0; 
	double math_avg = Math.round((double)math_sum / students.length * 100) / 100.0; 
		
	System.out.println("과목합계\t" + kor_sum + "\t" + eng_sum + "\t" + math_sum);
	System.out.println("과목평균\t" + kor_avg + "\t" + eng_avg + "\t" + math_avg);
}