java如何對(duì)類的對(duì)象進(jìn)行排序

有時(shí)我們需要對(duì)類按照類中的某一個(gè)屬性（或者多個(gè)屬性）來對(duì)類的對(duì)象進(jìn)行排序，有兩種方法可以實(shí)現(xiàn)，一種方法是類實(shí)現(xiàn)Comparable<T>接口，然后調(diào)用Collections.sort(List)方法進(jìn)行排序，另一種方法是類不實(shí)現(xiàn)Comparable<T>接口，而在排序時(shí)使用Collections.sort(List, Comparator<T>)方法，并實(shí)現(xiàn)其中的Comparator<T>接口。

先創(chuàng)建一個(gè)簡(jiǎn)單的學(xué)生類：

public class Student {
    
    private String name;
    
    private int age;
 
    public Student() {}
 
    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public int getAge() {
        return age;
    }
 
    public void setAge(int age) {
        this.age = age;
    }
}

1、通過類實(shí)現(xiàn)Comparable<T>接口進(jìn)行排序

public class Student implements Comparable<Student>{
 
    private String name;
 
    private int age;
 
    public Student() {}
 
    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public int getAge() {
        return age;
    }
 
    public void setAge(int age) {
        this.age = age;
    }
 
    /**
     * 將對(duì)象按姓名字典序升序排序
     * @param o
     * @return
     */
    @Override
    public int compareTo(Student o) {
        return this.name.compareTo(o.getName());
    }
 
    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

2、通過在Collections.sort()方法中實(shí)現(xiàn)Comparable<T>接口來實(shí)現(xiàn)排序

public class Client {
 
    public static void main(String[] args){
        List<Student> students = new ArrayList<>();
        students.add(new Student("a", 18));
        students.add(new Student("c", 19));
        students.add(new Student("b", 20));
 
        Collections.sort(students, new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                return o1.getAge()>o2.getAge()? -1:(o1.getAge()==o2.getAge()? 0:1);
            }
        });
        for(Student student:students){
            System.out.println(student.toString());
        }
    }
 
}

總結(jié)

無論使用上面的哪一種方法，對(duì)對(duì)象排序的核心是實(shí)現(xiàn)比較函數(shù)，其中第二種方法比第一種方法更加靈活。

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