Java 如何从对象列表中删除重复元素

如何从图书列表中删除重复元素，其中作者和语言相同，但标题不同

在这种情况下，我想删除任意两个位置（因为它们具有相同的作者和语言）：

我想删除任何一个位置（因为他们有相同的作者和语言）：

图书类别：

public class Book {
    private String author;
    private String language;
    private String title;
    
    public Book(String author, String language, String title) {
        this.author = author;
        this.language = language;
        this.title = title;
    }
    
    public void setTitle(String title) {
        this.title = title;
    }
    
    public String getTitle() {
        return this.title;
    }
    
    public void setLanguage(String language) {
        this.language = language;
    }
    
    public String getLanguage() {
        return this.language;
    }
    
    public void setAuthor(String author) {
        this.author = author;
    }
    
    public String getAuthor() {
        return this.author;
    }
}

Main.class：

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<Book> books = new ArrayList<Book>();
        books.add(new Book("Hemigway","english","Old man"));
        books.add(new Book("Willis","english","Black and white"));
        books.add(new Book("Hemigway","english","Lord of the ring"));
        books.add(new Book("Harper Lee","english","Mockingbird"));
        books.add(new Book("Fitzgerald","english","The catcher"));
        books.add(new Book("Hemigway","english","Border life"));
        books.add(new Book("Harper Lee","english","Other books"));
        
        for(Book book : books) {
            System.out.println(book.getAuthor() + " : "+book.getLanguage()+" : "+book.getTitle());
        }
        
    }

}

import java.util.ArrayList；
导入java.util.List；
公共班机{
公共静态void main（字符串[]args）{
List books=new ArrayList（）；
新增（新书（“海米威”、“英语”、“老人”）；
新增（新书（“威利斯”、“英语”、“黑白”）；
新增（新书（“海米威”、“英语”、“魔戒”）；
新增（新书（“哈珀·李”、“英语”、“模仿鸟”）；
新增（新书（“菲茨杰拉德”、“英语”、“捕手”）；
增加（新书（“海米威”、“英语”、“边境生活”）；
增加（新书（“哈珀·李”、“英语”、“其他书”）；
用于（书籍：书籍）{
System.out.println（book.getAuthor（）+”：“+book.getLanguage（）+”：“+book.getTitle（））；
}
}
}

您应该使用两个概念

设置

equal（）和hashcode

这是代码，使用Main方法中的Set

import java.util.HashSet;
import java.util.Objects;
import java.util.Set;

public class Main {
    public static void main(String[] args) {
        Set<Book> books = new HashSet<>();
        books.add(new Book("Hemigway","english","Old man"));
        books.add(new Book("Willis","english","Black and white"));
        books.add(new Book("Hemigway","english","Lord of the ring"));
        books.add(new Book("Harper Lee","english","Mockingbird"));
        books.add(new Book("Fitzgerald","english","The catcher"));
        books.add(new Book("Hemigway","english","Border life"));
        books.add(new Book("Harper Lee","english","Other books"));

        for(Book book : books) {
            System.out.println(book.getAuthor() + " : "+book.getLanguage()+" : "+book.getTitle());
        }

    }
}

以下是输出：

Harper Lee : english : Mockingbird
Fitzgerald : english : The catcher
Hemigway : english : Old man
Willis : english : Black and white

---

您只需使用

equals

和

hashcode

以及

stream

和

distinct

方法即可实现这一点

更改Books类以包括以下方法

class Book {

    /*
     * your already written code here. Add following in addition to your code
     * */

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Book book = (Book) o;
        return author.equalsIgnoreCase(book.author) && language.equalsIgnoreCase(book.language);
    }

    @Override
    public int hashCode() {
        return Objects.hash(author, language);
    }
}

现在将main方法更改为具有不同对象的新列表

public static void main(String[] args) {

    /*
     * your already written code here. Add following in addition to your code
     * */

    List<Book> newBooks = books.stream().distinct().collect(Collectors.toList());

    for (Book book : newBooks)
        System.out.println(book.getAuthor() + " : " + book.getLanguage() + " : " + book.getTitle());

}

publicstaticvoidmain（字符串[]args）{
/*
*您已经在此处编写了代码。除了代码之外，还添加以下内容
* */
List newBooks=books.stream（）.distinct（）.collect（Collectors.toList（））；
用于（书籍：新书）
System.out.println（book.getAuthor（）+”：“+book.getLanguage（）+”：“+book.getTitle（））；
}

但是如果它有不同的标题。。。你为什么认为是复制品？@Jordy我想他想说的是过滤掉那些相似的东西

Harper Lee : english : Mockingbird
Fitzgerald : english : The catcher
Hemigway : english : Old man
Willis : english : Black and white

class Book {

    /*
     * your already written code here. Add following in addition to your code
     * */

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Book book = (Book) o;
        return author.equalsIgnoreCase(book.author) && language.equalsIgnoreCase(book.language);
    }

    @Override
    public int hashCode() {
        return Objects.hash(author, language);
    }
}

public static void main(String[] args) {

    /*
     * your already written code here. Add following in addition to your code
     * */

    List<Book> newBooks = books.stream().distinct().collect(Collectors.toList());

    for (Book book : newBooks)
        System.out.println(book.getAuthor() + " : " + book.getLanguage() + " : " + book.getTitle());

}