简单了解java自定义和自然排序

package test;
public class Emp implements Comparable {
  private String name;
  private int 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 Emp() {
    super();
  }
  public Emp(String name, int age) {
    super();
    this.name = name;
    this.age = age;
  }
  @Override
  public String toString() {
    return "Emp [name=" + name + ", age=" + age + "]";
  }
  @Override
  public int compareTo(Object o) {
    if(o instanceof Emp){
      Emp emp = (Emp) o;
//     return this.age-emp.getAge();//按照年龄升序排序
      return this.name.compareTo(emp.getName());//换姓名升序排序
    }
    throw new ClassCastException("不能转换为Emp类型的对象...");
  }

}

package test;

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

import org.junit.BeforeClass;
import org.junit.Test;
public class TestSort {
  static List list = new ArrayList();
  //@BeforeClass注解标注的方法会在其它测试方法执行之前先执行,
  //且只执行一次.@Before注解标注的方法会在每个测试方法之前执行;
  //此处初始化集合只需要一次,因此使用@BeforeClass.
  @BeforeClass
  public static void init(){
    list.add(new Emp("tom",18));
    list.add(new Emp("jack",20));
    list.add(new Emp("rose",15));
    list.add(new Emp("jerry",17));
    System.out.println("排序前:");
    for(Object o : list){
      System.out.println(o);
    }
  }
  /**按age升序排序*/
// @Test
// public void testSortAge(){
//   Collections.sort(list);
//   System.out.println("自然排序按age排序后:");
//   for(Object o : list){
//     System.out.println(o);
//   }
// }
// 
  /**按name升序排序*/
  @Test
  public void testSortName(){
    Collections.sort(list);
    System.out.println("自然排序按name升序排序后:");
    for(Object o : list){
      System.out.println(o);
    }
  }
  /**使用Comparator比较器按age升序排序*/
  @Test
  public void testComparatorSortAge(){
    Collections.sort(list,new Comparator () {
      @Override
      public int compare(Object o1, Object o2) {
        if(o1 instanceof Emp && o2 instanceof Emp){
          Emp e1 = (Emp) o1;
          Emp e2 = (Emp) o2;
          return e1.getAge() - e2.getAge();
        }
        throw new ClassCastException("不能转换为Emp类型");
      }
    });
    System.out.println("使用Comparator比较器按age升序排序后:");
    for(Object o : list){
      System.out.println(o);
    }
  }
  /**使用Comparator比较器按name升序排序*/
  @Test
  public void testComparatorSortName(){
    Collections.sort(list,new Comparator () {
      @Override
      public int compare(Object o1, Object o2) {
        if(o1 instanceof Emp && o2 instanceof Emp){
          Emp e1 = (Emp) o1;
          Emp e2 = (Emp) o2;
          return e1.getName().compareTo(e2.getName());
        }
        throw new ClassCastException("不能转换为Emp类型");
      }
    });
    System.out.println("使用Comparator比较器按name升序排序后:");
    for(Object o : list){
      System.out.println(o);
    }
  }

}

排序前:
Emp [name=tom, age=18]
Emp [name=jack, age=20]
Emp [name=rose, age=15]
Emp [name=jerry, age=17]
自然排序按name升序排序后:
Emp [name=jack, age=20]
Emp [name=jerry, age=17]
Emp [name=rose, age=15]
Emp [name=tom, age=18]
使用Comparator比较器按age升序排序后:
Emp [name=rose, age=15]
Emp [name=jerry, age=17]
Emp [name=tom, age=18]
Emp [name=jack, age=20]
使用Comparator比较器按name升序排序后:
Emp [name=jack, age=20]
Emp [name=jerry, age=17]
Emp [name=rose, age=15]
Emp [name=tom, age=18]