第17章(中)--集合

1.ArrayList底层结构和源码分析

ArrayList的全面说明

1) Resizable-array implementation of the List interface [ArrayList实现了List的接口，底层是一个数组，并实现可变的功能.]
ArrayList 属性： transient Object[] elementData;

2) Implements all optional list operations [ArrayList实现了List所有的操作。

3) permits all elements, including null [ArrayList 可以添加任意的元素，包括null]

4) this class provides methods to manipulate the size of the array that is used internally to store the list[ArrayList的数据是保存到array ]

5) This class is roughly equivalent to Vector, except that it is unsynchronized [ArrayList 和Vector基本相同，除了Vector是线程同步的，ArrayList不是线程同步.]

2. Vector底层结构和ArrayList的比较

Vector的基本介绍

1) Vector类的定义说明

2) The Vector class implements a growable array of objects [Vector底层也是一个可变对象数组]

3) Vector 是线程同步的，即线程安全, Vector类的操作方法带有synchronized

public synchronized E get(int index) {

if (index >= elementCount)

throw new ArrayIndexOutOfBoundsException(index);

return elementData(index);

}

4) 在开发中，主要使用ArrayList ,只有在确实需要线程同步安全时，才考虑使用Vector(坦克大战)

3.LinkedList

4. ArrayList和LinkedList的比较【记住】

如何选择ArrayList和LinkedList：

1) 如果我们改查的操作多，选择ArrayList

2) 如果我们增删的操作多，选择LinkedList

3) 一般来说，在程序中，80%-90%都是查询，因此大部分情况下会选择ArrayList

4) 在一个项目中，根据业务灵活选择，也可能这样，一个模块使用的是ArrayList,另外一个模块是LinkedList.

5.set接口

6. Set接口实现类-HashSet

7.HashSet注意事项

、

 1 import java.util.HashSet;
 2 
 3 public class HashSetOverrideHashCodeEq {
 4 
 5     public static void main(String[] args) {
 6         // TODO Auto-generated method stub
 7         //需求是如果Car 的name 和price 一样，也就是说某个对象的属性完全一样，
 8         //我们认为是同一个对象。这时需要重写hashCode和equals
 9         
10         //System.out.println(new Car("奥迪", 300000).hashCode());
11         //System.out.println(new Car("奥迪", 300000).hashCode());
12         
13         //System.out.println(new Car("奥迪", 300000).equals(new Car("奥迪", 300000)));//true
14         
15         HashSet set = new HashSet();
16         set.add(new Car("奥拓", 1000));
17         set.add(new Car("奥迪", 300000));
18         set.add(new Car("法拉利", 10000000));
19         set.add(new Car("保时捷", 70000000));
20         set.add(new Car("奥迪", 300000));
21         for (Object object : set) {
22             System.out.println(object);
23         }
24 
25     }
26 
27 }
28 
29 class Car {
30     private String name;
31     private double price;
32 
33     
34     //使用eclipse生成 
35     //这里hashCode将属性考虑到. 如果我们的属性相同，则hashCode就相同
36 //    @Override
37     public int hashCode() {
38         final int prime = 31;
39         int result = 1;
40         result = prime * result + ((name == null) ? 0 : name.hashCode());
41         long temp;
42         temp = Double.doubleToLongBits(price);
43         result = prime * result + (int) (temp ^ (temp >>> 32));
44         return result;
45     }
46 
47     //这里比较时重写equals
48 //    @Override
49     public boolean equals(Object obj) {
50         if (this == obj)
51             return true;
52         if (obj == null)
53             return false;
54         if (getClass() != obj.getClass())
55             return false;
56         Car other = (Car) obj;
57         if (name == null) {
58             if (other.name != null)
59                 return false;
60         } else if (!name.equals(other.name))
61             return false;
62         if (Double.doubleToLongBits(price) != Double.doubleToLongBits(other.price))
63             return false;
64         return true;
65     }
66 
67     
68     public Car(String name, double price) {
69         super();
70         this.name = name;
71         this.price = price;
72     }
73 
74     
75     public String getName() {
76         return name;
77     }
78 
79     public void setName(String name) {
80         this.name = name;
81     }
82 
83     public double getPrice() {
84         return price;
85     }
86 
87     public void setPrice(double price) {
88         this.price = price;
89     }
90 
91     @Override
92     public String toString() {
93         return "Car [name=" + name + ", price=" + price + "]";
94     }

8.HashSet案例

  1 import java.util.HashSet;
  2 
  3 public class HashSetExercise {
  4 
  5     public static void main(String[] args) {
  6         // TODO Auto-generated method stub
  7         HashSet set = new HashSet();
  8         set.add(new Employee("jack", (short)80, new MyDate((short)2011, (short)11, (short)11)));
  9         set.add(new Employee("jack", (short)81, new MyDate((short)2011, (short)11, (short)11)));
 10         set.add(new Employee("jack", (short)82, new MyDate((short)2011, (short)11, (short)11)));
 11         set.add(new Employee("jack", (short)83, new MyDate((short)2011, (short)11, (short)11)));
 12         set.add(new Employee("jack", (short)83, new MyDate((short)2011, (short)11, (short)12)));
 13         set.add(new Employee("jack2", (short)83, new MyDate((short)2011, (short)11, (short)11)));
 14         
 15         for (Object object : set) {
 16             System.out.println(object);
 17         }
 18     }
 19 
 20 }
 21 
 22 //HashSet课堂练习
 23 //
 24 //定义一个Employee类，
 25 //该类包含：private成员属性name,age,birthday，其中 birthday 为 MyDate类(属性包括：year, month, day)的对象, 要求:
 26 //为每一个属性定义 getter, setter 方法；
 27 //并重写 toString 方法输出 name, age, birthday
 28 //认为 name和birthday一样的为同一个员工
 29 //要求MyDate的hashCode 和 equals使用自动生成重写
 30 //Employee 的hashCode和 equals 我们自己手动重写。 
 31 
 32 class MyDate{
 33     private short year;
 34     private short month;
 35     private short day;
 36     public MyDate(short year, short month, short day) {
 37         super();
 38         this.year = year;
 39         this.month = month;
 40         this.day = day;
 41     }
 42     public short getYear() {
 43         return year;
 44     }
 45     public void setYear(short year) {
 46         this.year = year;
 47     }
 48     public short getMonth() {
 49         return month;
 50     }
 51     public void setMonth(short month) {
 52         this.month = month;
 53     }
 54     public short getDay() {
 55         return day;
 56     }
 57     public void setDay(short day) {
 58         this.day = day;
 59     }
 60     @Override
 61     public String toString() {
 62         return "MyDate [year=" + year + ", month=" + month + ", day=" + day + "]";
 63     }
 64     @Override
 65     public int hashCode() {
 66         final int prime = 31;
 67         int result = 1;
 68         result = prime * result + day;
 69         result = prime * result + month;
 70         result = prime * result + year;
 71         return result;
 72     }
 73     @Override
 74     public boolean equals(Object obj) {
 75         if (this == obj)
 76             return true;
 77         if (obj == null)
 78             return false;
 79         if (getClass() != obj.getClass())
 80             return false;
 81         MyDate other = (MyDate) obj;
 82         if (day != other.day)
 83             return false;
 84         if (month != other.month)
 85             return false;
 86         if (year != other.year)
 87             return false;
 88         return true;
 89     }
 90     
 91     
 92     
 93 }
 94 
 95 class Employee{
 96     private String name;
 97     private short age;
 98     private MyDate birthday;
 99     
100     //认为 name和birthday一样的为同一个员工
101     
102     
103     public Employee(String name, short age, MyDate birthday) {
104         super();
105         this.name = name;
106         this.age = age;
107         this.birthday = birthday;
108     }
109     @Override
110     public int hashCode() {
111         return name.hashCode() + birthday.hashCode();
112     }
113     @Override
114     public boolean equals(Object obj) {
115         if(this == obj){
116             return true;
117         }
118         if(!(obj instanceof Employee)){
119             return false;
120         }
121         Employee e = (Employee)obj;
122         return name.equals(e.name) && birthday.equals(e.getBirthday());
123     }
124     public String getName() {
125         return name;
126     }
127     public void setName(String name) {
128         this.name = name;
129     }
130     public short getAge() {
131         return age;
132     }
133     public void setAge(short age) {
134         this.age = age;
135     }
136     public MyDate getBirthday() {
137         return birthday;
138     }
139     public void setBirthday(MyDate birthday) {
140         this.birthday = birthday;
141     }
142     @Override
143     public String toString() {
144         return "Employee [name=" + name + ", age=" + age + ", birthday=" + birthday + "]";
145     }
146     
147 }

9. Set接口实现类-TreeSet

10. TreeSet的自然排序

1.1.1 TreeSet实现Comprable 接口指定排序规则

 1 package com.atguigu.chapter15.treeset;
 2 
 3 import java.util.TreeSet;
 4 
 5 
 6 //按名字的升序排序，再按照价格的降序.
 7 public class TreeSetCompareableDemo {
 8 
 9     public static void main(String[] args) {
10         // TODO Auto-generated method stub
11         TreeSet set = new TreeSet();
12         set.add(new Book("摆渡人",30));
13         set.add(new Book("嫌疑人X的献身",45));
14         set.add(new Book("小时代",23));
15         set.add(new Book("小时代",23));
16         set.add(new Book("小时代",23));
17         set.add(new Book("摆渡人",31));
18         set.add(new Book("摆渡人",32));
19         set.add(new Book("流浪地球",45.8));
20         set.add(new Book("摆渡人",33));
21         
22         for (Object object : set) {
23             System.out.println(object);
24         }
25         
26         
27         
28         
29 
30     }
31 
32 }
33 
34 class Book implements Comparable{
35     private String name;
36     private double price;
37     public Book(String name, double price) {
38         super();
39         this.name = name;
40         this.price = price;
41     }
42     public String getName() {
43         return name;
44     }
45     public void setName(String name) {
46         this.name = name;
47     }
48     public double getPrice() {
49         return price;
50     }
51     public void setPrice(double price) {
52         this.price = price;
53     }
54     
55     //按名字的升序排序，再按照价格的降序.
56     @Override
57     public int compareTo(Object o) {
58         if(!(o instanceof Book)) {
59             return 0;
60         }
61         Book book = (Book)o;
62         if(name.compareTo(book.name) > 0){
63             return -1;
64         }else if (name.compareTo(book.name) < 0){
65             return 1;
66         }else {
67             if (price > book.getPrice()){
68                 return 1;
69             }else if(price < book.getPrice()){
70                 return -1;
71             }else {
72                 return 0; //返回0,加入不到TreeSet
73             }
74         }
75     }
76     @Override
77     public String toString() {
78         return "Book [name=" + name + ", price=" + price + "]";
79     }
80     
81     
82     
83 }

1.1.1 TreeSet通过构造器传入Comparator 匿名对象定制排序

 1 mport java.util.Comparator;
 2 import java.util.TreeSet;
 3 
 4 public class TreeSetComparatorDemo {
 5 
 6     public static void main(String[] args) {
 7         // TODO Auto-generated method stub
 8         // 要求按照价格从小到大排序即(不考虑书名)
 9         TreeSet set = new TreeSet(new Comparator() {
10 
11             @Override
12             public int compare(Object o1, Object o2) {
13                 // TODO Auto-generated method stub
14                 Book book1 = (Book)o1;
15                 Book book2 = (Book)o2;
16                 return Double.compare(book1.getPrice(), book2.getPrice());
17             }
18         });
19         
20         set.add(new Book("摆渡人",30));
21         set.add(new Book("嫌疑人X的献身",45));
22         set.add(new Book("小时代",23));
23         set.add(new Book("小时代",23));
24         set.add(new Book("小时代",23));
25         set.add(new Book("摆渡人",31));
26         set.add(new Book("摆渡人",32));
27         set.add(new Book("流浪地球",45.8));
28         set.add(new Book("摆渡人",33));
29         
30         for (Object object : set) {
31             System.out.println(object);
32         }
33     }
34 
35 }

posted @ 2020-06-24 13:18 --学无止境-- 阅读(227) 评论(0) 编辑收藏举报

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第17章(中)--集合

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