我們先看幾個比較常見的排序例子，基本資料型別的排序
List list = Arrays.asList(1,3,2,5,4); list.sort(Comparator.naturalOrder()); System.out.println(list); list.sort(Comparator.reverseOrder()); System.out.println(list); 输出结果： [1, 2, 3, 4, 5] [5, 4, 3, 2, 1]
我們可以看到執行結果是符合預期的，但是多數場景我們可能需要針對物件的某個屬性進行排序，那麼該怎麼做呢？我們看下邊的例子：
public class Student {
private String name;
private String sexual;
private Integer age;
public Student(String name, String sexual,Integer age) {
this.name = name;
this.sexual = sexual;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSexual() {
return sexual;
}
public void setSexual(String sexual) {
this.sexual = sexual;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", sexual='" + sexual + '\'' +
", age=" + age +
'}';
}
public class Starter {
public static void main(String[] args) {
List<Student> list = Arrays.asList(
new Student("jack", 12),
new Student("john", 13),
new Student("lily", 11),
new Student("lucy", 10)
);
list.sort(Comparator.comparing(Student::getAge));
System.out.println(list);
list.sort(Comparator.comparing(Student::getAge).reversed());
System.out.println(list);
}
}
输出结果：
[Student{name='lucy', age=10}, Student{name='lily', age=11}, Student{name='jack', age=12}, Student{name='john', age=13}]
[Student{name='john', age=13}, Student{name='jack', age=12}, Student{name='lily', age=11}, Student{name='lucy', age=10}]如果我們需要按照性別分組再排序又該如何實現呢？我們接著看下邊的例子
public class Starter {
public static void main(String[] args) {
List<Student> list = Arrays.asList(
new Student("jack", "male", 12),
new Student("john", "male", 13),
new Student("lily", "female", 11),
new Student("david", "male", 14),
new Student("luck", "female", 13),
new Student("jones", "female", 15),
new Student("han", "male", 13),
new Student("alice", "female", 11),
new Student("li", "male", 12)
);
Map<String, List<Student>> groupMap = list.stream().sorted(Comparator.comparing(Student::getAge))
.collect(Collectors.groupingBy(Student::getSexual, Collectors.toList()));
System.out.println(groupMap.toString());
}
}
输出结果：
{
female = [
Student {
name = 'lily', sexual = 'female', age = 11
},
Student {
name = 'alice', sexual = 'female', age = 11
}, Student {
name = 'luck', sexual = 'female', age = 13
}, Student {
name = 'jones', sexual = 'female', age = 15
}],
male = [
Student {
name = 'jack', sexual = 'male', age = 12
}, Student {
name = 'li', sexual = 'male', age = 12
}, Student {
name = 'john', sexual = 'male', age = 13
}, Student {
name = 'han', sexual = 'male', age = 13
}, Student {
name = 'david', sexual = 'male', age = 14
}]
}我們看到上邊的輸出結果存在一個問題，如果年齡相同則沒有按照姓名排序，怎麼實現這個功能呢？我們接著看下邊的例子
Map<String, List<Student>> groupMap = list.stream().sorted(Comparator.comparing(Student::getAge)
.thenComparing(Student::getName)).collect(Collectors.groupingBy(Student::getSexual, Collectors.toList()));
输出结果：
{
female = [
Student {
name = 'alice', sexual = 'female', age = 11
}, Student {
name = 'lily', sexual = 'female', age = 11
}, Student {
name = 'luck', sexual = 'female', age = 13
}, Student {
name = 'jones', sexual = 'female', age = 15
}],
male = [
Student {
name = 'jack', sexual = 'male', age = 12
}, Student {
name = 'li', sexual = 'male', age = 12
}, Student {
name = 'han', sexual = 'male', age = 13
}, Student {
name = 'john', sexual = 'male', age = 13
}, Student {
name = 'david', sexual = 'male', age = 14
}]
}以上是Java中如何用lambda表達式來排序的詳細內容。更多資訊請關注PHP中文網其他相關文章！
