集合08/Set接口:Set实现类(二)

本是古典何须时尚 2023-10-04 16:52 13阅读 0赞

### Set接实现类之二：LinkedHashset（HashSet的子类） ###

LinkedHashSet作为HashSet的子类，在添加数据的同时，每个数据还维护了两个引用，记录此数据前一个数据和后一个数据。  
优点:对于频繁的遍历操作，LinkedHashSet效率高于HashSet

--------------------

### Set接实现类之三：TreeSet ###

1.  向Treeset中添加的数据，要求是相同类的对象。
2.  两种排序方式:**自然排序实现（Comparable接口）  
    和定制排序**

> 自然排序中，比较两个对象是否相同的标准为: compareTo()返回e.不再是equals().  
> 定制排序中，比较两个对象是否相同的标准为:compare()返回e.不再是equals().

> ![在这里插入图片描述][6a9e7e90a64d442ea8380801663b8d9f.png]

#### 自然排序 ####

##### 举例一 #####

package com.jh.SET;
    
    
    import org.junit.Test;
    
    import java.util.Iterator;
    import java.util.Set;
    import java.util.TreeSet;
    
    public class SetTest {
        
    
        @Test
        public void test1(){
        
            Set set = new TreeSet();
            set.add(-34);
            set.add(34);
            set.add(1);
            set.add(5);
            set.add(20);
    
            Iterator iterator = set.iterator();
            while(iterator.hasNext()){
        
                System.out.println(iterator.next());
            }
        }
    }

> 结果  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70]

##### 举例二 #####

package com.jh.SET;
    
    
    import org.junit.Test;
    import java.util.Iterator;
    import java.util.Set;
    import java.util.TreeSet;
    
    public class SetTest {
        
    
        @Test
        public void test1(){
        
            Set set = new TreeSet();
            set.add(new User("Tom",12));
            set.add(new User("Jerry",32));
            set.add(new User("Jim",3));
            set.add(new User("Mike",44));
            set.add(new User("Jack",15));
    
            Iterator iterator = set.iterator();
            while(iterator.hasNext()){
        
                System.out.println(iterator.next());
            }
        }
    }

package com.jh.SET;
    
    //实现Comparable
    public class User implements Comparable {
        
        private String name;
        private int age;
    
        public User() {
        
        }
    
        public User(String name, int age) {
        
            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 String toString() {
        
            return "User{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    
        //equals方法
    
        @Override
        public boolean equals(Object o) {
        
            System.out.println("User equals()......");
    
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
    
            User user = (User) o;
    
            if (age != user.age) return false;
            return name != null ? name.equals(user.name) : user.name == null;
        }
    
        @Override
        public int hashCode() {
        
            int result = name != null ? name.hashCode() : 0;
            result = 31 * result + age;
            return result;
        }
    
        //按照姓名从小到大排列
        @Override
        public int compareTo(Object o) {
        
            if (o instanceof User) {
        
                User user = (User) o;
                return this.name.compareTo(user.name);
            }else{
        
                throw new RuntimeException("输入的类型不匹配");
            }
        }
    }

> 结果  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 1]

但是这种排序会漏掉元素，因为判断相同的标准不为equals用的compareTo()

--------------------

package com.jh.SET;
    
    
    import org.junit.Test;
    import java.util.Iterator;
    import java.util.Set;
    import java.util.TreeSet;
    
    public class SetTest {
        
    
        @Test
        public void test1(){
        
            Set set = new TreeSet();
            set.add(new User("Tom",12));
            set.add(new User("Jerry",32));
            set.add(new User("Jim",3));
            set.add(new User("Mike",44));
            set.add(new User("Jack",15));
            set.add(new User("Jack",50));//同名不同年龄
    
            Iterator iterator = set.iterator();
            while(iterator.hasNext()){
        
                System.out.println(iterator.next());
            }
        }
    }

> 结果：Jack少了一个（User用的一个）  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 2]

> 改进Uesr

package com.jh.SET;
    
    //实现Comparable
    public class User implements Comparable {
        
        private String name;
        private int age;
    
        public User() {
        
        }
    
        public User(String name, int age) {
        
            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 String toString() {
        
            return "User{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    
        //equals方法
    
        @Override
        public boolean equals(Object o) {
        
            System.out.println("User equals()......");
    
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
    
            User user = (User) o;
    
            if (age != user.age) return false;
            return name != null ? name.equals(user.name) : user.name == null;
        }
    
        @Override
        public int hashCode() {
        
            int result = name != null ? name.hashCode() : 0;
            result = 31 * result + age;
            return result;
        }
    
        //按照姓名从大到小排列，年龄从小到大排列
        @Override
        public int compareTo(Object o) {
        
            if (o instanceof User) {
        
                User user = (User) o;
                //return this.name.compareTo(user.name);
                int compare = -this.name.compareTo(user.name);
                if (compare != 0){
        
                    return compare;
                }else{
        
                    return Integer.compare(this.age,user.age);
                }
            }else{
        
                throw new RuntimeException("输入的类型不匹配");
            }
        }
    }

> 改进的地方：  
> ![在这里插入图片描述][c8062c1394c2446481acff4e940b6c4e.png]  
> 结果  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 3]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 4]

--------------------

#### 定制排序 ####

package com.jh.SET;
    
    import org.junit.Test;
    
    import java.util.Comparator;
    import java.util.Iterator;
    import java.util.TreeSet;
    
    public class TreeSetTest {
        
        @Test
        public void test() {
        
            Comparator com = new Comparator() {
        
    
                //按照年龄从小到大排列
                @Override
                public int compare(Object o1, Object o2) {
        
                    if (o1 instanceof User && o2 instanceof User) {
        
                        User u1 = (User) o1;
                        User u2 = (User) o2;
                        return Integer.compare(u1.getAge(), u2.getAge());
                    } else {
        
                        throw new RuntimeException("输入的数据类型不匹配");
                    }
                }
            };
    
            TreeSet set = new TreeSet(com);
            set.add(new User("Tom", 12));
            set.add(new User("Jerry", 32));
            set.add(new User("Jim", 3));
            set.add(new User("Mike", 44));
            set.add(new User("Jack", 15));
            set.add(new User("Jack", 50));//同名不同年龄
    
            Iterator iterator = set.iterator();
            while (iterator.hasNext()) {
        
                System.out.println(iterator.next());
            }
        }
    }

> 结果：用的改进Uesr  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 5]

> 定制排序中，比较两个对象是否相同的标准为: **compare()返回e.不再是equaLs().**

[6a9e7e90a64d442ea8380801663b8d9f.png]: https://img-blog.csdnimg.cn/6a9e7e90a64d442ea8380801663b8d9f.png
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[c8062c1394c2446481acff4e940b6c4e.png]: https://img-blog.csdnimg.cn/c8062c1394c2446481acff4e940b6c4e.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 3]: https://img-blog.csdnimg.cn/902397f399f04ed6af56486961e8b9d8.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
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