类定义(课下选做)

Posted 2021-02-15 wyf20175217

一、设计思路

• 之前在课上做过类似的题目，首先分析，这个题的重点在重写toString类和equals类
• 首先，是toString类，直接重写public String toString(){return 字符串；}返回要输出的字符串即可
• 然后是equals类
  • 用public boolean equals(Object o){内容}重写
  • 先用if(this==o)判断地址是否相同，若相同直接true
  • 再用if(o==null)判断对象是否为空```
  • 接着用if (getClass()!=o.getClass())判断对象类型是否相等
  • 最后判断成员变量是否相等
  • 为提高程序效率，应重写hasCode方法

二、代码

Book.java

public class Book {
    String name;
    String auther;
    String publish;
    String date;
    Book(){}
    Book(String name){}
    Book(String auther,String publish,String date){}
    Book(String name,String auther,String publish,String date){
        this.name=name;
        this.auther=auther;
        this.publish=publish;
        this.date=date;
    }
    public void setName(String name){
        this.name=name;
    }
    public String getName(){
        return name;
    }
    public void setAuther(String auther){
        this.auther=auther;
    }
    public String getAuther(){
        return auther;
    }
    public void setPublish(String publish){
        this.publish=publish;
    }
    public String getPublish(){
        return publish;
    }
    public void setDate(String date){
        this.date=date;
    }
    public String getDate(){
        return date;
    }
    public String toString(){                  //重写toString类
        return "书名："+name+"，作者："+auther+"，出版社："+publish+"，出版日期："+date;
    }
    public boolean equals(Object o){
        if (this==o)        //判断地址是否相等，若相等，直接返回true
            return true;
        if (o==null)         //判断对象是否为空
            return false;
        if (getClass()!=o.getClass())    //判断对象类型是否相等
            return false;
        Book book=(Book)o;         //向下转型，判断成员变量是否相等
        if (book.name==this.name&&book.auther==this.auther&&book.publish==this.publish&&book.date==this.date)
            return true;
        else
            return false;
    }
        public int hashCode() {                 //重写hasCode类，提高程序效率
        int result = name.hashCode();
        result = 31 * result + auther.hashCode();
        result = 31 * result + publish.hashCode();
        result = 31 * result + date.hashCode();
        return result;
    }
}

bookShelf.java

public class bookShelf {
    public static void main(String[] args){
        Book b0 = new Book("Java","耿祥义","清华大学出版社","2017.9");
        Book b1 = new Book("汇编语言与程序设计","钱晓捷","电子工业出版社","2018.6");
        Book b2 = new Book("计算机网络","谢希仁","电子工业出版社","2017.1");
        System.out.println(b0.toString());
        System.out.println(b1.toString());
        System.out.println(b2.toString());
        System.out.println(b0.getName());
        System.out.println(b1.getAuther());
        System.out.println(b2.getDate());
        System.out.println(b0.equals(b1));
        System.out.println(b2.equals(b2));
    }
}

三、运行结果截图

四、码云代码链接

• 码云链接

五、参考资料

• 重写equals()方法