Java 实现对Arrays类 自定义 排序sort的2种方法

一、实现Comparable接口(用于类之间的排序)：

 假设有Employee类，有name和salary字段，

需要实现Comparable<T>接口：

public class Employee implements Comparable<Employee> {
    private String name;
    private double salary;
 
    public Employee() {
    }
 
    public Employee(String name, double salary) {
        this.name = name;
        this.salary = salary;
    }
 
    public void raiseSalary(double byPercent) {
        double raise = salary * byPercent / 100;
        salary += raise;
    }
 
    /*
    * Compares employees by salary
    * @param other another Employee object
    * return a negative value if this employee has a lower salary than
    * otherObject , 0 if the salaries are the same, a positive value otherwise
    */
    public int compareTo(Employee other) {
        return Double.compare(salary, other.salary);
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public double getSalary() {
        return salary;
    }
 
    public void setSalary(double salary) {
        this.salary = salary;
    }
}

假设希望根据雇员的薪水进行比较，要实现compareTo方法：

public int compareTo(Object otherObject)
{
    Employee other = (Employee) otherObject;
    return Double.compare(salary, other.salary);
}

我们来测试一下，这个比较排序是否能成功：

 
import java.util.Arrays;
 
 
public class Test {
    public static void main(String[] args) {
        Employee[] staff = new Employee[5];
        staff[0] = new Employee("Harry Hacker", 35000);
        staff[1] = new Employee("Carl Cracker", 75000);
        staff[2] = new Employee("Tony Tester", 38000);
        staff[3] = new Employee("Tony Bool", 48000);
        staff[4] = new Employee("June Bo", 48001);
        Arrays.sort(staff);
        // print out information about all Employee objects
        for (Employee e : staff) {
            System.out.println("name=" + e.getName() + " , salary=" + e.getSalary());
        }
    }
}

输出结果为：

name=Harry Hacker , salary=35000.0
name=Tony Tester , salary=38000.0
name=Tony Bool , salary=48000.0
name=June Bo , salary=48001.0
name=Carl Cracker , salary=75000.0

排序是可以的。

所以，排序可以实现Comparable接口，然后自定义compareTo方法即可（因为sort方法要有提供对象比较的方式）。

 

二、使用比较器（comparator）作为sort的参数（用于单个类型的排序）：

比较器实现了Comparator接口

如： 需要按照字符的长度递增来进行排序：

 
import java.util.Arrays;
import java.util.Comparator;
 
public class Test {
    public static void main(String[] args) {
 
        String[] friends = { "Peter", "Paulllll", "Mary" };
        Arrays.sort(friends, new LengthComparator());
        for (String f : friends) {
            System.out.print(f + " ");
        }
    }
 
    static class LengthComparator implements Comparator<String>
    {
        public int compare(String first, String second) {
            return first.length()- second.length();
        }
    }
 
}

输出结果为：

Mary Peter Paulllll 

排序按字符长度递增顺序。

 

如果只是需要按照字符的字典顺序排序的话，则不需要实现Comparator:

public class Test {
    public static void main(String[] args) {
        String[] friends = { "Peter", "Paulllll", "Mary","ziqizh" ,"yoyo"};
        Arrays.sort(friends);
        for (String f : friends) {
            System.out.print(f + " ");
        }
    }
 
    static class LengthComparator implements Comparator<String>
    {
        public int compare(String first, String second) {
            return first.length()- second.length();
        }
    }
 
}

输出结果为：

 
Mary Paulllll Peter yoyo ziqizh 

 

C++也有类似的排序，单个类型或者是结构体都可以，自己写一个比较函数cmp，作为sort的参数排序即可。

 

Java内容具体可以参照《Java核心技术卷1》6.2章节