Comparable接口
Arrays类中的sort方法会对对象数组进行排序，但前提是对象所属的类必须实现了Comparable接口。
例：使用Comparable接口对学生对象数组排序（按学生年龄排序）
public class ComparableStudent {
public static void main(String[] args) {
//构造三个学生对象放入数组
Student student1 = new Student("小明",12);
Student student2 = new Student("小红",11);
Student student3 = new Student("小刚",14);
Student[] students = {student1,student2,student3};
System.out.println("排序前：\n" + Arrays.toString(students));
//排序
Arrays.sort(students);
System.out.println("排序后：\n" + Arrays.toString(students));
}
}
class Student implements Comparable<Student> {
private String name;
private Integer age;
public Student(String name, Integer age) {
this.name = name;
this.age = age;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
@Override
public int compareTo(Student o) {
return Integer.compare(age, o.age);
}
}
打印结果：
排序前：
[Student{name='小明', age=12}, Student{name='小红', age=11}, Student{name='小刚', age=14}]
排序后：
[Student{name='小红', age=11}, Student{name='小明', age=12}, Student{name='小刚', age=14}]
Comparator接口
Arrays.sort()还有第二种用法，就是一个数组和比较器作为参数，比较器必须实现Comparator接口。
例：使用Comparator接口对学生对象数组排序（按学生年龄排序）
public class ComparatorStudent {
public static void main(String[] args) {
//构造三个学生对象放入数组
Student1 student1 = new Student1("小明", 12);
Student1 student2 = new Student1("小红", 11);
Student1 student3 = new Student1("小刚", 14);
Student1[] students = {student1, student2, student3};
System.out.println("排序前：\n" + Arrays.toString(students));
//排序
Arrays.sort(students, new AgeComparator());
System.out.println("排序后：\n" + Arrays.toString(students));
}
}
/**
* 学生类
*/
class Student1 {
private String name;
private Integer age;
public Student1(String name, Integer age) {
this.name = name;
this.age = age;
}
@Override
public String toString() {
return "Student1{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
public String getName() {
return name;
}
public Integer getAge() {
return age;
}
}
/**
* 比较器
*/
class AgeComparator implements Comparator<Student1> {
@Override
public int compare(Student1 o1, Student1 o2) {
return o1.getAge() - o2.getAge();
}
}
打印结果：
排序前：
[Student1{name='小明', age=12}, Student1{name='小红', age=11}, Student1{name='小刚', age=14}]
排序后：
[Student1{name='小红', age=11}, Student1{name='小明', age=12}, Student1{name='小刚', age=14}]
lambda表达式
java8的lambda表达式可以简单快速地实现用比较器的方式对对象数组排序。
例：使用lambda表达式接口对学生对象数组排序（按学生年龄排序）
public class LambdaStudent {
public static void main(String[] args) {
//构造三个学生对象放入数组
Student2 student1 = new Student2("小明", 12);
Student2 student2 = new Student2("小红", 11);
Student2 student3 = new Student2("小刚", 14);
Student2[] students = {student1, student2, student3};
System.out.println("排序前：\n" + Arrays.toString(students));
//排序
Arrays.sort(students, (s1, s2) -> s1.getAge() - s2.getAge());
System.out.println("排序后：\n" + Arrays.toString(students));
}
}
class Student2 {
private String name;
private Integer age;
public Student2(String name, Integer age) {
this.name = name;
this.age = age;
}
@Override
public String toString() {
return "Student2{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
public String getName() {
return name;
}
public Integer getAge() {
return age;
}
}
打印结果：
排序前：
[Student1{name='小明', age=12}, Student1{name='小红', age=11}, Student1{name='小刚', age=14}]
排序后：
[Student1{name='小红', age=11}, Student1{name='小明', age=12}, Student1{name='小刚', age=14}]
