如何排序在Java中对象的数组？ [英] How to sort an array of objects in Java?

问题描述

我的阵列中不包含任何字符串。但其包含的对象引用。每一个对象引用由toString方法返回姓名，ID，作者和出版商。

My array does not contain any string. But its contains object references. Every object reference returns name, id, author and publisher by toString method.

public String toString() {
        return (name + "\n" + id + "\n" + author + "\n" + publisher + "\n");
}

现在我需要排序的名称数组对象。我知道如何排序，但我不知道如何从这些对象中提取的名称和排序。

Now I need to sort that array of objects by the name. I know how to sort, but I do not know how to extract the name from the objects and sort them.

推荐答案

您有两种方式来做到这一点，无论使用的阵列实用工具类

You have two ways to do that, both use the Arrays utility class

1. 实施一个比较并通过你与比较的<一个沿阵列href=\"http://docs.oracle.com/javase/7/docs/api/java/util/Arrays.html#sort%28T%5B%5D,%20java.util.Comparator%29\"相对=nofollow>其中把它作为第二个参数排序的方法。


2. 实施在可比接口类你的对象距离，并通过阵列的<一个href=\"http://docs.oracle.com/javase/7/docs/api/java/util/Arrays.html#sort%28java.lang.Object%5B%5D%29\"相对=nofollow>排序方法其中仅采用一个参数。

1. Implement a Comparator and pass your array along with the comparator to the sort method which take it as second parameter.
2. Implement the Comparable interface in the class your objects are from and pass your array to the sort method which takes only one parameter.

示例

class Book implements Comparable<Book> {
    public String name, id, author, publisher;
    public Book(String name, String id, String author, String publisher) {
        this.name = name;
        this.id = id;
        this.author = author;
        this.publisher = publisher;
    }
    public String toString() {
        return ("(" + name + ", " + id + ", " + author + ", " + publisher + ")");
    }
    @Override
    public int compareTo(Book o) {
        // usually toString should not be used,
        // instead one of the attributes or more in a comparator chain
        return toString().compareTo(o.toString());
    }
}

@Test
public void sortBooks() {
    Book[] books = {
            new Book("foo", "1", "author1", "pub1"),
            new Book("bar", "2", "author2", "pub2")
    };

    // 1. sort using Comparable
    Arrays.sort(books);
    System.out.println(Arrays.asList(books));

    // 2. sort using comparator: sort by id
    Arrays.sort(books, new Comparator<Book>() {
        @Override
        public int compare(Book o1, Book o2) {
            return o1.id.compareTo(o2.id);
        }
    });
    System.out.println(Arrays.asList(books));
}

输出

[(bar, 2, author2, pub2), (foo, 1, author1, pub1)]
[(foo, 1, author1, pub1), (bar, 2, author2, pub2)]

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