定义一个图书类Book

/**
 * 定义一个图书类Book
 * 属性包括:书名name(String类型)、作者author(String类型)、单价price(double类型)、数量amount(int类型)，并且所有属性为私有。
 * 提供一个为书名name、作者author、单价price和数量amount指定初值的构造方法
 * 为私有属性提供访问器方法。但要求书名和作者一旦初始化之后不能修改
 * 提供计算图书总价的方法totalPrice方法，图书总价 = 单价 * 数量
 * 定义测试类BookTest,在其main方法中创建一个书名为“Java”、作者为“张三”、单价为“30”、数量为“2000”的图书，并计算输出该图书的总价
 */

public class BookTest{
    public static void main(String[] args) {
        Book book = new Book("Java","张三",30,2000);
        System.out.println(book.totalPrice());
    }
}
class Book{
    private String name;
    private String author;
    private double price;
    private int amount;

    public Book(String name, String author, double price, int amount) {
        this.name = name;
        this.author = author;
        this.price = price;
        this.amount = amount;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public int getAmount() {
        return amount;
    }

    public void setAmount(int amount) {
        this.amount = amount;
    }

    public double totalPrice(){
        return this.price * this.amount;
    }
}