我的数组不包含任何字符串。但它包含对象引用。每个对象引用都通过toString方法返回name，id，author和publisher。
public String toString() {
return (name + "\n" + id + "\n" + author + "\n" + publisher + "\n");
}
现在我需要按名称对对象数组进行排序。我知道如何排序，但我不知道如何从对象中提取名称并对它们进行排序。
答案 0 :(得分：35)
您可以尝试这样的事情：
List<Book> books = new ArrayList<Book>();
Collections.sort(books, new Comparator<Book>(){
public int compare(Book o1, Book o2)
{
return o1.name.compareTo(o2.name);
}
});
答案 1 :(得分：31)
您有两种方法可以使用Arrays实用程序类
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));
}
<强>输出
[(bar, 2, author2, pub2), (foo, 1, author1, pub1)]
[(foo, 1, author1, pub1), (bar, 2, author2, pub2)]
答案 2 :(得分：22)
Arrays.sort(myTypes, (a,b) -> a.name.compareTo(b.name));
<强> Test.java
public class Test {
public static void main(String[] args) {
MyType[] myTypes = {
new MyType("John", 2, "author1", "publisher1"),
new MyType("Marry", 298, "author2", "publisher2"),
new MyType("David", 3, "author3", "publisher3"),
};
System.out.println("--- before");
System.out.println(Arrays.asList(myTypes));
Arrays.sort(myTypes, (a, b) -> a.name.compareTo(b.name));
System.out.println("--- after");
System.out.println(Arrays.asList(myTypes));
}
}
<强> MyType.java
public class MyType {
public String name;
public int id;
public String author;
public String publisher;
public MyType(String name, int id, String author, String publisher) {
this.name = name;
this.id = id;
this.author = author;
this.publisher = publisher;
}
@Override
public String toString() {
return "MyType{" +
"name=" + name + '\'' +
", id=" + id +
", author='" + author + '\'' +
", publisher='" + publisher + '\'' +
'}' + System.getProperty("line.separator");
}
}
<强>输出：
--- before
[MyType{name=John', id=2, author='author1', publisher='publisher1'}
, MyType{name=Marry', id=298, author='author2', publisher='publisher2'}
, MyType{name=David', id=3, author='author3', publisher='publisher3'}
]
--- after
[MyType{name=David', id=3, author='author3', publisher='publisher3'}
, MyType{name=John', id=2, author='author1', publisher='publisher1'}
, MyType{name=Marry', id=298, author='author2', publisher='publisher2'}
]
Arrays.sort(myTypes, MyType::compareThem);
必须在 MyType.java 中添加compareThem：
public static int compareThem(MyType a, MyType b) {
return a.name.compareTo(b.name);
}
答案 3 :(得分：4)
假设一个checkMarkImage类具有一个Book字段获取器，则可以通过传递一个使用Java 8构造指定的附加name-Comparator default method来使用Arrays.sort方法。 ＆method references。
Comparator此外，还可以使用Arrays.sort(bookArray, Comparator.comparing(Book::getName));
方法在多个字段上进行比较。
thenComparing答案 4 :(得分：1)
java 8 使用引用方法
您可以将compare方法添加到Book类
class Book {
public static int compare(Book a , Book b)
{
return a.name.compareTo(b.name);
}
}
然后你可以这样做：
Arrays.sort(books , Book::compare);
这是完整的例子：
static class Book {
String name;
String author;
public Book(String name, String author) {
this.name = name;
this.author = author;
}
public static int compareBooks(Book a , Book b)
{
return a.name.compareTo(b.name);
}
@Override
public String toString() {
return "name : " + name + "\t" + "author : " + author;
}
}
public static void main(String[] args) {
Book[] books = {
new Book("Book 3" , "Author 1"),
new Book("Book 2" , "Author 2"),
new Book("Book 1" , "Author 3"),
new Book("Book 4" , "Author 4")
};
Arrays.sort(books , Book::compareBooks);
Arrays.asList(books).forEach(System.out::println);
}
答案 5 :(得分：1)
[Employee(name=John, age=25, salary=3000.0, mobile=9922001),
Employee(name=Ace, age=22, salary=2000.0, mobile=5924001),
Employee(name=Keith, age=35, salary=4000.0, mobile=3924401)]
public void whenComparing_thenSortedByName() {
Comparator<Employee> employeeNameComparator
= Comparator.comparing(Employee::getName);
Arrays.sort(employees, employeeNameComparator);
assertTrue(Arrays.equals(employees, sortedEmployeesByName));
}
结果
[Employee(name=Ace, age=22, salary=2000.0, mobile=5924001),
Employee(name=John, age=25, salary=3000.0, mobile=9922001),
Employee(name=Keith, age=35, salary=4000.0, mobile=3924401)]
答案 6 :(得分：0)
有时您希望对任意值的对象数组进行排序。由于compareTo（）始终使用与实例相同的信息，因此您可能希望使用其他技术。一种方法是使用标准排序算法。让我们假设您有一系列书籍，并且您希望对它们的高度进行排序，它们存储为int并可通过getHeight（）方法访问。以下是如何对数组中的书籍进行排序的方法。 （如果您不想更改原始数组，只需复制并对其进行排序。）
`int tallest; // the index of tallest book found thus far
Book temp; // used in the swap
for(int a = 0; a < booksArray.length - 1; a++) {
tallest = a; // reset tallest to current index
// start inner loop at next index
for(int b = a + 1; b < booksArray.length; b++)
// check if the book at this index is taller than the
// tallest found thus far
if(booksArray[b].getHeight() > booksArray[tallest].getHeight())
tallest = b;
// once inner loop is complete, swap the tallest book found with
// the one at the current index of the outer loop
temp = booksArray[a];
booksArray[a] = booksArray[tallest];
booksArray[tallest] = temp;
}`
完成此代码后，Book对象的数组将按高度按降序排序 - 这是室内设计师的梦想！
答案 7 :(得分：0)
您可以在要比较其对象的类上实现“可比较”接口。
并在其中实现“ compareTo”方法。
在ArrayList中添加类的实例
然后，“ java.utils.Collections.sort（）”方法将起到必要的作用。
这是一个->（https://deva-codes.herokuapp.com/CompareOnTwoKeys）的工作示例，其中根据对象的两个键首先按id然后按名称对对象进行排序。
答案 8 :(得分：0)
Arrays.sort(yourList,new Comparator<YourObject>() {
@Override
public int compare(YourObjecto1, YourObjecto2) {
return compare(o1.getYourColumn(), o2.getYourColumn());
}
});
答案 9 :(得分：-1)
public class Student implements Comparable<Student> {
private int sid;
private String sname;
public Student(int sid, String sname) {
super();
this.sid = sid;
this.sname = sname;
}
public int getSid() {
return sid;
}
public void setSid(int sid) {
this.sid = sid;
}
public String getSname() {
return sname;
}
public void setSname(String sname) {
this.sname = sname;
}
@Override
public String toString() {
return "Student [sid=" + sid + ", sname=" + sname + "]";
}
public int compareTo(Student o) {
if (this.getSname().compareTo(o.getSname()) > 1) {
return toString().compareTo(o.getSname());
} else if (this.getSname().compareTo(o.getSname()) < 1) {
return toString().compareTo(o.getSname());
}
return 0;
}
}
答案 10 :(得分：-1)
import java.util.Collections;
import java.util.List;
import java.util.ArrayList;
public class Test {
public static void main(String[] args) {
List<Student> str = new ArrayList<Student>();
str.add(new Student(101, "aaa"));
str.add(new Student(104, "bbb"));
str.add(new Student(103, "ccc"));
str.add(new Student(105, "ddd"));
str.add(new Student(104, "eee"));
str.add(new Student(102, "fff"));
Collections.sort(str);
for(Student student : str) {
System.out.println(student);
}
}
}