class Book {

    String name;

    int price;

    int num;
//构造方法之间的互相调用解决了代码的重复问题，但是一定要留出口

    public Book() {

        this("请输入书名",,);

    }

    public Book(String name) {

        this(name,,);//this调用方法

    }

    public Book(String name,int num) {

        this(name,num,);

    }

    public Book(String name,int num,int price) {

        this.name = name; //this调用属性

        this.price = price;

        this.num = num;

    }

    public String getInfo() {

        return "书名: "+this.name+"\n"+

                "数目: "+this.num+"\n" +

                "单价: " +this.price;

    }

} 

public class test1 {

    public static void main(String args[]) {

        Book book_0 =  new Book();

        Book book_1 =  new Book("我的世界");

        Book book_2 =  new Book("老人与海",);

        Book book_3 =  new Book("陆炳勋",,);

        System.out.println(book_0.getInfo());

        System.out.println(book_1.getInfo());

        System.out.println(book_2.getInfo());

        System.out.println(book_3.getInfo());

    }

}