Set重写hashCode和equals方法实现引用对象去重

运作原理：

首先判断hashCode是否相同，如果不同，直接判定为两个不同的对象。如果hashCode相同，再去比较equals是否一样，如果一样，则为同一个对象。如果不一样，则是两个不同对象。

那么直接上代码：

Book.java

package SetNoDoubleFuction01;

public class Book {
    private String name;
    private Integer price;
    private  String press;
    private  String author;

    public String getName() {
        return name;
    }

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

    public Integer getPrice() {
        return price;
    }

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

    public String getPress() {
        return press;
    }

    public void setPress(String press) {
        this.press = press;
    }

    public String getAuthor() {
        return author;
    }

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

    public Book() {
        super();
    }

    public Book(String name, Integer price, String press, String author) {
        this.name = name;
        this.price = price;
        this.press = press;
        this.author = author;
    }
　　　//hashCode判断结果不同才会执行equals　
    //所以hashCode和equals都会参与判断（而且hashCode会先行进行判断）
    public int hashCode(){
        return name.hashCode()+price.hashCode()+press.hashCode()+author.hashCode();
    };
  //equals不能省略（hashCode并不能起到完全判断）
    public boolean equals(Object obj){
        System.out.println("++++++++++++++++++++++++++++++++++++++");
       //用来查看equals运行了几次
        if (this == obj) return true;

        if (obj == null) return false;

        if(this.getClass() != obj.getClass()) return false;

        Book book=(Book) obj;
        if (this.name.equals(book.name)&& this.price.equals(book.price))
            return true;

        return false;

    };

    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + '\'' +
                ", price=" + price +
                ", press='" + press + '\'' +
                ", author='" + author + '\'' +
                '}'+ this.hashCode();
    }


}

 

Test01.java

package SetNoDoubleFuction01;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

public class test01 {

    static Set<Book> set = new HashSet<>();
   //随便加几条数据
    static Book book1 =new Book("laogao", 2, "憨批", "学生01");
    static Book book2= new Book("wangfei", 1, "2233", "学生02");
    static Book book3= new Book("123", 3, "报刊", "学生03");
    static Book book4= new Book("33", 5, "2333", "学生04");
    static Book book5= new Book("老色批", 4, "2报", "学生05");
    //加入重复数据用来测试
    static Book book6= new Book("33", 5, "2333", "学生04");
    static Book book7= new Book("33", 5, "2333", "学生04");

    public static void main(String[] args) {
        set.add(book1);
        set.add(book2);
        set.add(book3);
        set.add(book4);
        set.add(book5);
        set.add(book6);
        set.add(book7);

        System.out.println("已有数据！！2");
        for (Book it:set) {
            System.out.println(it.toString());
        }
        System.out.println("增加新内容？");

       /* System.out.println(book4.equals(book7));*/
        //控制台输入数据测试
        Scanner sc = new Scanner(System.in);
        Book book99=new Book();
        System.out.println("请输入姓名：");
        book99.setName(sc.next());
        System.out.println("请输入编号：");
        book99.setPrice(sc.nextInt());
        System.out.println("请输入类型：");
        book99.setPress(sc.next());
        System.out.println("请输入作者：");
        book99.setAuthor(sc.next());

        set.add(book99);
        for (Book it:set) {
            System.out.println(it.toString());
        }


    }





}

结果（去重成功！！）