Java에서 캡슐화의 역할은 무엇입니까? 단계는 무엇입니까?

package com.qfedu.test1;

public class Student {
	private  String name;
	private int age;
	private double score;
	
	public void setName(String name) {
		this.name = name;
	}
	public String getName() {
		return name;
	}
	
	public void  setAge(int age) {
		if(age > 0 && age <= 140) {
			this.age = age;
		}else {
			System.out.println("年龄不合适，使用默认年龄");
			this.age = 18;
		}
	}
	
	public int getAge() {
		return age;
	}
	
	public void setScore(double score) {
		if(score >= 0 && score <= 100 ) {
			this.score = score;
		}else {
			System.out.println("分数不合适，使用默认分数");
			this.score = 60;
		}
	}
	
	public double getScore() {
		return score;
	}
	
	public void printStu() {
		System.out.println("学生名字是" + name);
		System.out.println("学生分数是" + this.getScore());
		System.out.println("学生的年龄是" + getAge());
	}
	
	public static void main(String[] args) {
		Student stu1 = new Student();
		stu1.name = "赵四";
		stu1.age = -20;
		stu1.score = -50;
		// 以上代码 在实际开发中不会将测试类和实体类写在一起
	}
}