您当前的位置： 首页 > 学无止境 > 心得笔记 网站首页心得笔记

【第13章：Java类集】_排序及重复元素说明

发布时间：2021-01-02 12:05:53编辑：雪饮阅读（）

TreeSet对于自定义类型数据的比较排序

import java.util.TreeSet;
import java.util.Set;
class Person{
       private String name;
       private int age;
       public Person(String name,int age){
              this.name=name;
              this.age=age;
       }
       public String toString(){
              return "姓名:"+this.name+",年龄:"+this.age;
       }
}
public class TestJava{
       public static void main(String args[]){
              Set<Person> allSet=new TreeSet<Person>();
              allSet.add(new Person("kasumi",28));
              allSet.add(new Person("ayane",27));
              allSet.add(new Person("moniji",29));
              allSet.add(new Person("snowDrink",24));
              System.out.println(allSet);
       }
}

可见TreeSet对数据进行排序的前提是该数据所在类型必须要实现比较器。
所以当我们程序增加比较器之后。
import java.util.TreeSet;
import java.util.Set;
class Person implements Comparable<Person>{
       private String name;
       private int age;
       public Person(String name,int age){
              this.name=name;
              this.age=age;
       }
       public String toString(){
              return "姓名:"+this.name+",年龄:"+this.age;
       }
       public int compareTo(Person per){
              if(this.age>per.age){
                     return 1;
              }
              if(this.age<per.age){
                     return -1;
              }
              return 0;
       }
}
public class TestJava{
       public static void main(String args[]){
              Set<Person> allSet=new TreeSet<Person>();
              allSet.add(new Person("kasumi",28));
              allSet.add(new Person("ayane",27));
              allSet.add(new Person("moniji",29));
              allSet.add(new Person("snowDrink",24));
              System.out.println(allSet);
       }
}
D:\>javac TestJava.java
D:\>java TestJava
[姓名:snowDrink,年龄:24, 姓名:ayane,年龄:27, 姓名:kasumi,年龄:28, 姓名:moniji,年龄:29]
现在我们将momiji的年龄修改的和kasumi的年龄一致，会发现momiji会被过滤掉了。
import java.util.TreeSet;
import java.util.Set;
class Person implements Comparable<Person>{
       private String name;
       private int age;
       public Person(String name,int age){
              this.name=name;
              this.age=age;
       }
       public String toString(){
              return "姓名:"+this.name+",年龄:"+this.age;
       }
       public int compareTo(Person per){
              if(this.age>per.age){
                     return 1;
              }
              if(this.age<per.age){
                     return -1;
              }
              return 0;
       }
}
public class TestJava{
       public static void main(String args[]){
              Set<Person> allSet=new TreeSet<Person>();
              allSet.add(new Person("kasumi",28));
              allSet.add(new Person("ayane",27));
              allSet.add(new Person("momoji",28));
              allSet.add(new Person("snowDrink",24));
              System.out.println(allSet);
       }
}
D:\>javac TestJava.java
D:\>java TestJava
[姓名:snowDrink,年龄:24, 姓名:ayane,年龄:27, 姓名:kasumi,年龄:28]
所以TreeSet接口去重操作是依赖自数据类中的比较器，而我们这里自定义的比较器仅仅比较了年龄。
所以我们改良下比较器，让其遇到name属性即String时就调用String的比较器。
import java.util.TreeSet;
import java.util.Set;
class Person implements Comparable<Person>{
       private String name;
       private int age;
       public Person(String name,int age){
              this.name=name;
              this.age=age;
       }
       public String toString(){
              return "姓名:"+this.name+",年龄:"+this.age;
       }
       public int compareTo(Person per){
              if(this.age>per.age){
                     return 1;
              }
              if(this.age<per.age){
                     return -1;
              }
              return this.name.compareTo(per.name);
       }
}
public class TestJava{
       public static void main(String args[]){
              Set<Person> allSet=new TreeSet<Person>();
              allSet.add(new Person("kasumi",28));
              allSet.add(new Person("ayane",27));
              allSet.add(new Person("momoji",28));
              allSet.add(new Person("snowDrink",24));
              System.out.println(allSet);
       }
}
D:\>javac TestJava.java
D:\>java TestJava
[姓名:snowDrink,年龄:24, 姓名:ayane,年龄:27, 姓名:kasumi,年龄:28, 姓名:momoji,年龄:28]
所以排序就完成了，并且momiji也没有被去除。
HashSet接口它是去重的但是对于自定义类型则就未必了
import java.util.Set;
import java.util.HashSet;
class Person{
       private String name;
       private int age;
       public Person(String name,int age){
              this.name=name;
              this.age=age;
       }
       public String toString(){
              return "姓名:"+this.name+",年龄:"+this.age;
       }
}
public class TestJava{
       public static void main(String args[]){
              Set<Person> allSet=new HashSet<Person>();
              allSet.add(new Person("kasumi",28));
              allSet.add(new Person("ayane",27));
              allSet.add(new Person("momoji",28));
              allSet.add(new Person("momoji",28));
              allSet.add(new Person("snowDrink",24));
              System.out.println(allSet);
       }
}
D:\>javac TestJava.java
D:\>java TestJava
[姓名:ayane,年龄:27, 姓名:kasumi,年龄:28, 姓名:momoji,年龄:28, 姓名:snowDrink,年龄:24, 姓名:momoji,年龄:28]
可以看到momiji出现两次且年龄都是28，但是却没有去重。
那么HashSet接口要想完成去重操作就类似于TreeSet接口完成排序操作一样，HashSet这里则是需要依赖于数据对象所在类的equals方法和hashCode方法，所以我们现在只需要对Person类中重写下这两个方法就可以完成Person的去重。
import java.util.Set;
import java.util.HashSet;
class Person{
       private String name;
       private int age;
       public Person(String name,int age){
              this.name=name;
              this.age=age;
       }
       public String toString(){
              return "姓名:"+this.name+",年龄:"+this.age;
       }
       public boolean equals(Object obj){
              if(this==obj){
                     return true;
              }
              if(!(obj instanceof Person)){
                     return false;
              }
              Person p=(Person)obj;
              if(this.name.equals(p.name) && this.age==p.age){
                     return true;
              }
              return false;
       }
       public int hashCode(){
              return this.name.hashCode()*this.age;
       }
}
public class TestJava{
       public static void main(String args[]){
              Set<Person> allSet=new HashSet<Person>();
              allSet.add(new Person("kasumi",28));
              allSet.add(new Person("ayane",27));
              allSet.add(new Person("momoji",28));
              allSet.add(new Person("momoji",28));
              allSet.add(new Person("snowDrink",24));
              System.out.println(allSet);
       }
}
D:\>javac TestJava.java
D:\>java TestJava
[姓名:kasumi,年龄:28, 姓名:ayane,年龄:27, 姓名:snowDrink,年龄:24, 姓名:momoji,年龄:28]