自定义对象比较排序输出的两种实现方式:匿名实现Comparator接口，重写compare方法;实现Comparable接口，重写compareTo方法

**实现方式一：
匿名实现Comparator接口，重写compare方法
代码示例：需求按年龄顺序输出学生类信息，若是你是年龄一致，按照字母顺序排列。
Student.java

public class Student {
private String name;
private int age;

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;
}

@Override
public String toString() {
    return "Student{" +
            "name='" + name + '\'' +
            ", age=" + age +
            '}';
}

}

SortDemo.java

public class SortDemo {
public static void main(String[] args) {
Student s1 = new Student("he",18);
Student s2 = new Student("she",18);
Student s3 = new Student("you",28);
Student s4 = new Student("see",20);
ArrayList<Student> list =new ArrayList<Student>();
list.add(s1);
list.add(s2);
list.add(s3);
list.add(s4);
list.sort(new Comparator<Student>() {
@Override
public int compare(Student s1, Student s2) {
int num = s1.getAge()-s2.getAge();
//三元条件，年龄一致时比较姓名首字母前后
int num2 = num==0?s1.getName().compareTo(s2.getName()):num;
return num2;
}
});
for (Student stu : list) {
System.out.println(stu.getName()+" "+stu.getAge());
}
}
}

**实现方式二：
实现Comparable接口，重写compareTo方法
Student2.java

public class Student2 implements Comparable<Student2> {
private String name;
private int age;

public Student2(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;
}

@Override
public String toString() {
    return "Student{" +
            "name='" + name + '\'' +
            ", age=" + age +
            '}';
}

@Override
public int compareTo(Student2 stu) {
    if (this.age - stu.age !=0){
        return this.age-stu.age;
    }else {
        //年龄一致时
        return this.getName().compareTo(stu.getName());
    }
}

}

SortDemo2.java

public class SortDemo2 {
public static void main(String[] args) {
ArrayList<Student2> list =new ArrayList<Student2>();
list.add(new Student2("she",18));
list.add(new Student2("he",18));
list.add(new Student2("you",28));
list.add(new Student2("see",20));
Collections.sort(list);
for (Student2 stu2 : list) {
System.out.println(stu2.getName()+" "+stu2.getAge());
}
}
}

from lj 2020.05.06