requirement

The definition class Student contains three attributes: Student number(int), grade state(int), grade
score(int). Create 20 student objects with student numbers from 1 to 20. Grades and grades are determined by random numbers.
Question 1: print out the student information of grade 3 (state value is 3).
***

I've written two versions, one of which is not encapsulation, the other is encapsulation

Implementation code without encapsulation:

package com.luokai.exer;
/*
 * The definition class Student contains three attributes: Student number(int), grade state(int), grade
score(int).  Create 20 student objects with student numbers from 1 to 20. Grades and grades are determined by random numbers.
Question 1: print out the student information of grade 3 (state value is 3).
***
Tips:
1) Generate random number: Math.random(), return value type double;
2) Rounding: Math.round(double d), return the value type long.
 */

public class StudentTest {
	/**
	 * @Description
	 * @author luokai Email:luokai524@163.com
	 * @date 2020 12:42:09 PM, June 2, 2010
	 * @param args
	 */
	public static void main(String[] args) {
		//Declare an array of Student type
		Student[] studs = new Student[20];//String[] arr = new String[10];
		for(int i = 0;i < studs.length;i++) {
			//Assign values to array elements
			studs[i] = new Student();
			//Assign a value to the property of the Student object
			//Student number [1,20]
			studs[i].number = (i + 1);
			//Grade [1,6]
			studs[i].state = (int)(Math.random() * (6 - 1 + 1) + 1);
			//Score [0100]
			studs[i].score = (int)(Math.random() * (100 - 0 + 1));		
		}
		
		//Traversing elements of all objects
		for(int i = 0;i < studs.length;i++) {
			//Method 1
			//System.out.println ***
			//Method 2
			//studs[i].showStudent();
			
			//Question 1: print out the student information of grade 3 (state value is 3).
			if(studs[i].state == 3) {
				studs[i].showStudent();
			}
		}
		System.out.println();
		
		//***
		for(int i = 0;i < studs.length - 1;i++) {
			for(int j = 0;j < studs.length - 1 - i;j++) {
				if(studs[j].score > studs[j + 1].score) {
					//If you need to reorder, exchange Student objects
					Student temp = studs[j];
					studs[j] = studs[j + 1];
					studs[j + 1] = temp;
				}
				
			}
		}
		//Traversing objects after bubble sorting
		for(int i = 0;i < studs.length;i++) {
			studs[i].showStudent();
		}
		
	}
	
}

class Student{
	int number;
	int state;
	int score;	
	
	//Traversing elements of all objects
	public void showStudent() {		
			System.out.println("Student ID:" + number + " Grade:" +state+ " Results:" + score);		
	}
}

Implementation code for encapsulation:

package com.luokai.exer;
/*
 * The definition class Student contains three attributes: Student number(int), grade state(int), grade
score(int).  Create 20 student objects with student numbers from 1 to 20. Grades and grades are determined by random numbers.
Question 1: print out the student information of grade 3 (state value is 3).
***
Tips:
1) Generate random number: Math.random(), return value type double;
2) Rounding: Math.round(double d), return the value type long.

 *This code is correct StudentTest.java The function of manipulating array is encapsulated in array
 */

public class StudentTestPlus {
	/**
	 * @Description
	 * @author luokai Email:luokai524@163.com
	 * @date 2020 12:42:09 PM, June 2, 2010
	 * @param args
	 */
	public static void main(String[] args) {
		//Declare an array of Student type
		StudentPlus[] studs = new StudentPlus[20];//String[] arr = new String[10];
		for(int i = 0;i < studs.length;i++) {
			//Assign values to array elements
			studs[i] = new StudentPlus();
			//Assign a value to the property of the Student object
			//Student number [1,20]
			studs[i].number = (i + 1);
			//Grade [1,6]
			studs[i].state = (int)(Math.random() * (6 - 1 + 1) + 1);
			//Score [0100]
			studs[i].score = (int)(Math.random() * (100 - 0 + 1));		
		}
		
		StudentTestPlus test = new StudentTestPlus();
		//Traverse StudentPlus array object		
		test.show(studs);
		System.out.println("*********************");
		//Query students of grade
		test.searchState(studs, 3);
		System.out.println("*********************");
		//Rank results
		test.sort(studs);
		
		
		
				
	}
	
	/**
	 * 
	 * @Description  Traversal of Student [] array
	 * @author luokai Email:luokai524@163.com
	 * @date 2020 8:14:44 PM, June 2, 2006
	 * @param studs
	 */
	public void show(StudentPlus[] studs) {
		for(int i = 0;i < studs.length;i++) {				
			studs[i].showStudent();					
			}
		System.out.println();
		}
	
	/**
	 * 		
	 * @Description ***
	 * @author luokai Email:luokai524@163.com
	 * @date 2020 ***
	 * @param studs
	 * @param state
	 */
	public void searchState(StudentPlus[] studs,int state) {
		//Traversing elements of all objects
		for(int i = 0;i < studs.length;i++) {
			if(studs[i].state == state) {
				studs[i].showStudent();
			}
		}
		System.out.println();
	}
	
	/**
	 * 
	 * @Description ***
	 * @author luokai Email:luokai524@163.com
	 * @date 2020 1:19:07 PM, June 2, 2010
	 * @param studs
	 */
	public void sort(StudentPlus[] studs) {
		for(int i = 0;i < studs.length - 1;i++) {
			for(int j = 0;j < studs.length - 1 - i;j++) {
				if(studs[j].score > studs[j + 1].score) {
					//If you need to reorder, exchange Student objects
					StudentPlus temp = studs[j];
					studs[j] = studs[j + 1];
					studs[j + 1] = temp;
				}
				
			}
		}
		
		//Traversing the student array after bubble sorting
		for(int i = 0;i < studs.length;i++) {
			studs[i].showStudent();
		}
		System.out.println();
	}
	
}

class StudentPlus{
	int number;
	int state;
	int score;	
	
	//Traversing elements of all objects
	public void showStudent() {		
			System.out.println("Student ID:" + number + " Grade:" +state+ " Results:" + score);		
	}
}