Java封装1-5编程练习，应该怎么改？

package com.imooc.test;

public class Book {

  //私有属性：书名、作者、出版社、价格

     private String title;

     private String author;

         private String publisher;

     private double price;

    //通过构造方法实现属性赋值 

      /*通过公有的get/set方法实现属性的访问，其中：

      1、限定图书价格必须大于10，如果无效需进行提示，并强制赋值为10

      2、限定作者、书名均为只读属性

      */

// 无参构造方法

public Book() {

}

//多参构造方法，实现对学号、姓名、性别、年龄的赋值

public Book(String title, String author, String publisher, double price) {

this.setTitle(title);

this.setAuthor(author);

this.setPublisher(publisher);

this.setPrice(price);

}

// 多参构造方法，实现对全部属性的赋值

public String getTitle() {

return title;

}

public void setTitle(String title) {

this.title = title;

}

public void setAuthor(String author) {

this.author = author;

}

public String getAuthor() {

return author;

}

public String getPublisher() {

return publisher;

}

public void setPublisher(String publisher) {

this.publisher = publisher;

}

public double getPrice() {

if (price < 10)

System.out.println("图书价格最低10元");

return price;

}

public void setPrice(double price) {

if (price < 10)

this.price = 10;

else

this.price = price;

}

public String introduction() {

String str = "书名：" + this.getTitle() + "\n作者：" + this.getAuthor() + "\n出版社："

+ this.getPublisher() + "\n价格：" + this.getPrice()+"元";

return str;

}

}

package com.imooc.test;

public class BookTest {

public static void main(String[] args) {

     //

      Book one = new Book("红楼梦", "曹雪芹", "人民文学出版社", 5);

      Book two = new Book("小李飞刀", "古龙", "中国长安出版社", 55.5);

     System.out.println(one.introduction());

     System.out.println("==========================");

     System.out.println(two.introduction());

}

}