java8 使用lamda表达式对list集合进行排序

java8 list集合内排序问题

list是java开发最常用的容器之一，有时需要对获取的list按照一定的规则排序。在java8之前我们一般会想到的两种方法是：（1）比较器，即实现Comparator接口，（2）自比较，实现Comparable接口。java8以后使用lamda表达式比较可以大大简化list集合排序的代码实现。下面我分别用这三种方法对list进行排序：
lamda表达式写法：
创建model类
package xcwlkj;

public class Student{

private String name;

private int age;

public Student(String name, int age) {
	super();
	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;
}

}

//main方法调试
package xcwlkj;

import java.util.ArrayList;
import java.util.List;

public class Test3 {
public static void main(String[] args) throws InterruptedException, ClassNotFoundException {

List stuList=new ArrayList();
stuList.add(new Student("xiaoming", 12));
stuList.add(new Student("xiaohua", 15));
stuList.add(new Student("xiaoli", 11));
/**lamda表达式内部调用compareTo方法，该方法只能比较字符串，排序字段为int需先转化*/
stuList.sort((h1, h2) -> String.valueOf(h1.getAge()).compareTo(String.valueOf(h2.getAge())));
stuList.forEach(item->System.out.println(item.getName()+"，年龄："+item.getAge()));

}
}
运行结果：

实现Comparable接口写法：
创建model类，在student类中实现Comparable接口，重写compareTo方法。
package xcwlkj;

public class Student implements Comparable{

private String name;

private int age;

public Student(String name, int age) {
	super();
	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 int compareTo(Student student) {

	return this.age-student.age;
}

}
//main方法调试：
package xcwlkj;

import java.util.ArrayList;
import java.util.List;

public class Test3 {
public static void main(String[] args) throws InterruptedException, ClassNotFoundException {

List stuList=new ArrayList();
stuList.add(new Student("xiaoming", 12));
stuList.add(new Student("xiaohua", 15));
stuList.add(new Student("xiaoli", 11));
Collections.sort(stuList);
for (int i = 0; i 

}
}
运行结果：

实现Comparator接口写法：
创建model类
package xcwlkj;

public class Student{

private String name;

private int age;

public Student(String name, int age) {
	super();
	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;
}

}
//main方法调试：
package xcwlkj;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Test3 {
public static void main(String[] args) throws InterruptedException, ClassNotFoundException {

List stuList=new ArrayList();
stuList.add(new Student("xiaoming", 12));
stuList.add(new Student("xiaohua", 15));
stuList.add(new Student("xiaoli", 11));
/**创建比较器实例*/
NewComparator comparator=new Test3().new NewComparator();
Collections.sort(stuList, comparator);
for (int i = 0; i 

}
//比较器
class NewComparator implements Comparator{

@Override
public int compare(Student student1, Student student2) {

	return student1.getAge()-student2.getAge();
}

}
}
运行结果：

三种方法都能实现对集合按照一定规则排序，java8的lamda表达式相较于之前的方法代码更简洁，不需要在model类实现comparable接口，也不需要构造比较器。直接在表达式内调用compareTo方法即可。