Java8：使用Lambda表达式增强版Comparator排序

学习路上的自我记录-------路好长，就问你慌不慌，大声港，不慌。----jstarseven。

实体类：

 package com.server.model;

 /**
  * Created by jstarseven on 2016/3/21.
  */
 public class Human {

     private String name;
     private int age;

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

     public Human() {
         super();
     }

     public Human(final String name, final 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;
     }

     public static int compareByNameThenAge(Human lhs, Human rhs) {
         if (lhs.getName().equals(rhs.getName())) {
             return lhs.getAge() - rhs.getAge();
         } else {
             return lhs.getName().compareTo(rhs.getName());
         }
     }

 }

测试类：

 package com.server.lambda;

 import com.server.model.Human;
 import org.junit.Test;

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

 /**
  * Created by jstarseven on 2016/3/21.
  */
 public class TestLambda {

     //    不使用Lambda表达式的基本排序
     @Test
     public void givenPreLambda_whenSortingEntitiesByName_thenCorrectlySorted() {

         List<Human> humans = new ArrayList();
         humans.add(new Human("A", 10));
         humans.add(new Human("C", 14));
         humans.add(new Human("C", 12));
         humans.add(new Human("B", 12));
         Collections.sort(humans, new Comparator<Human>() {
             public int compare(Human o1, Human o2) {
                 return o1.getName().compareTo(o2.getName());
             }
         });
         for (Human bean : humans) {
             System.out.println(bean.toString());
         }
     }

     //    使用Lambda表达式的基本排序
     @Test
     public void whenSortingEntitiesByName_thenCorrectlySorted() {
         List<Human> humans = new ArrayList();
         humans.add(new Human("A", 10));
         humans.add(new Human("C", 14));
         humans.add(new Human("C", 12));
         humans.add(new Human("B", 12));
         humans.sort((Human h1, Human h2) -> h1.getName().compareTo(h2.getName()));
         for (Human bean : humans) {
             System.out.println(bean.toString());
         }
     }

     //    没有类型定义（ Type Definitions）的基本排序
     @Test
     public void givenLambdaShortForm_whenSortingEntitiesByName_thenCorrectlySorted() {
         List<Human> humans = new ArrayList();
         humans.add(new Human("A", 10));
         humans.add(new Human("C", 14));
         humans.add(new Human("C", 12));
         humans.add(new Human("B", 12));
         humans.sort((h1, h2) -> h1.getName().compareTo(h2.getName()));
         for (Human bean : humans) {
             System.out.println(bean.toString());
         }
     }

     //    使用静态方法的引用来排序
     @Test
     public void givenMethodDefinition_whenSortingEntitiesByNameThenAge_thenCorrectlySorted() {
         List<Human> humans = new ArrayList();
         humans.add(new Human("A", 10));
         humans.add(new Human("C", 14));
         humans.add(new Human("C", 12));
         humans.add(new Human("B", 12));
         humans.sort(Human::compareByNameThenAge);
         for (Human bean : humans) {
             System.out.println(bean.toString());
         }
     }

     //    提取Comparator进行排序
     @Test
     public void givenInstanceMethod_whenSortingEntitiesByNameThenAge_thenCorrectlySorted() {
         List<Human> humans = new ArrayList();
         humans.add(new Human("A", 10));
         humans.add(new Human("C", 14));
         humans.add(new Human("C", 12));
         humans.add(new Human("B", 12));
         Collections.sort(humans, Comparator.comparing(Human::getName));
         for (Human bean : humans) {
             System.out.println(bean.toString());
         }
     }

     //    反转排序
     @Test
     public void whenSortingEntitiesByNameReversed_thenCorrectlySorted() {
         List<Human> humans = new ArrayList();
         humans.add(new Human("A", 10));
         humans.add(new Human("C", 14));
         humans.add(new Human("C", 12));
         humans.add(new Human("B", 12));
         Comparator<Human> comparator = (h1, h2) -> h1.getName().compareTo(h2.getName());

         humans.sort(comparator.reversed());
         for (Human bean : humans) {
             System.out.println(bean.toString());
         }
     }

     //    多条件排序
     @Test
     public void whenSortingEntitiesByNameThenAge_thenCorrectlySorted() {
         List<Human> humans = new ArrayList();
         humans.add(new Human("A", 10));
         humans.add(new Human("C", 14));
         humans.add(new Human("C", 12));
         humans.add(new Human("B", 12));
         humans.sort((lhs, rhs) -> {
             if (lhs.getName().equals(rhs.getName())) {
                 return lhs.getAge() - rhs.getAge();
             } else {
                 return lhs.getName().compareTo(rhs.getName());
             }
         });
         for (Human bean : humans) {
             System.out.println(bean.toString());
         }
     }

     //    多条件组合排序
     @Test
     public void givenComposition_whenSortingEntitiesByNameThenAge_thenCorrectlySorted() {
         List<Human> humans = new ArrayList();
         humans.add(new Human("A", 10));
         humans.add(new Human("C", 14));
         humans.add(new Human("C", 12));
         humans.add(new Human("B", 12));
         humans.sort(Comparator.comparing(Human::getName).thenComparing(Human::getAge));
         for (Human bean : humans) {
             System.out.println(bean.toString());
         }
     }
 }

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