类定义

Posted 2021-02-15 wangzihong0213

类定义

一、题目要求

设计并实现一个Book类，定义义成Book.java,Book 包含书名，作者，出版社和出版日期，这些数据都要定义getter和setter。定义至少三个构造方法，接收并初始化这些数据。覆盖（Override）toString方法，返回良好的含有多行的书的描述信息。覆盖equals方法，书名，作者，出版社和出版日期完全一致才说明两本书是一样的。
创建一个测试类Bookshelf, 其中的main方法创建并更新几个Book对象。Book至少包含三本本学期教材内容。

二、设计思路

• 题目本身并不难理解，实现也比较容易，重点在于如何重写toString()方法和equals()方法
• 首先定义构造方法，这个只需要写出最全的然后做一些删减即可
• 然后重写toString()方法，，先去搜索了一下toString()类的功能，发现只要将它写成字符串形式即可

• 之后又去搜索了一下equals()方法，并百度了相关的重写方法，equals()方法的重写操作步骤比较多

  • 先判断对象地址是否相同if(this==obj)
  • 判断对相关是否为空if(obj==null)
  • 判断对象类型是否一致if(getClass() != obj.getClass())
  • 判断是否为该类创建的对象if(!(obj instanceof Book))
  • 最后用成员变量判断是否完全相同即可

• 重写hashCode()方法

public int hashCode() {???
    return Objects.hash(name,author,publish,date);
}

三、代码

package PublicDefinition;
import java.util.Objects;
public class Book {??? 
    String name;??? 
    String author;??? 
    String publish;??? 
    String date;??? 
    Book(String name,String author) {}??? 
    Book(String name,String author,String publish) {}??? 
    Book(String name,String author,String publish,String date) {
        this.name = name;??????? 
        this.author = author;??????? 
        this.publish = publish;??????? 
        this.date = date;??? 
    }??? 
    public void setName(String name) {??????? 
        this.name = name;??? 
    }??? 
    public void setAuthor(String author) {??????? 
        this.author = author;??? 
    }??? 
    public void setPublish(String publish) {??????? 
        this.publish = publish;??? 
    }??? 
    public void setDate(String date) {??????? 
        this.date = date;??? 
    }??? 
    public String getName() {??????? 
        return name;??? 
    }??? 
    public String getAuthor() {??????? 
        return author;??? 
    }??? 
    public String getPublish() {??????? 
        return publish;??? 
    }??? 
    public String getDate() {??????? 
        return date;??? 
    }??? 
    public String toString() {??????? 
        return "书名为"+name+" 作者是"+author+" 出版社为"+publish+" 出版日期是"+date;??? 
    }??? 
    public boolean equals(Object obj) {??????? 
        if(this == obj) {??????????? 
            return true;??????? 
        }??????? 
        if(obj == null) {??????????? 
            return false;??????? 
        }??????? 
        if(getClass() != obj.getClass()) {??????????? 
            return false;??????? 
        }??????? 
        if(!(obj instanceof Book)){??????????? 
            return false;??????? 
        }??????? 
        else {??????????? 
            Book book = (Book)obj;??????????? 
            return
        Objects.equals(name,book.name)&&Objects.equals(author,book.author)&&Objects.equals(publish,book.publish)&&Objects.equals(date,book.date);??????? 
        }??? 
    }??? 
    public int hashCode() {??????? 
        return Objects.hash(name,author,publish,date);??? 
    }
}

package PublicDefinition;
public class Bookshelf {??? 
    public static void main(String[] args) {??????? 
        Book b1 = new Book("Java2实用教程（第五版）","耿祥义","清华大学出版社","2017年1月");??????? 
        Book b2 = new Book("密码学","郑秀林","金城出版社","2016年8月");??????? 
        Book b3 = new Book("计算机网络","谢希仁","电子工业出版社","2017年1月");??????? 
        System.out.println(b1);??????? 
        System.out.println(b2);??????? 
        System.out.println(b3);??????? 
        System.out.println(b1.getDate());??????? 
        System.out.println(b2.getPublish());??????? 
        System.out.println(b3.getAuthor());??????? 
        System.out.println(b1.getName());??????? 
        System.out.println(b1.equals(b2));??????? 
        System.out.println(b2.equals(b3));??????? 
        System.out.println(b2.equals(b2));??? 
    }
}

四、运行结果截图

五、代码托管

https://gitee.com/wangzihong/20175209/tree/master/src/PublicDefinition

六、参考资料

• 重写toString()方法
• 重写equals()方法
• 重写hashCode()方法