集合框架-ArrayList练习(去除ArrayList集合中的重复元素)

 1 package cn.itcast.p3.arraylist.test;
 2
 3 import java.util.ArrayList;
 4 import java.util.Iterator;
 5
 6 import com.sun.org.apache.bcel.internal.generic.NEW;
 7
 8 import cn.itcast.p.bean.Person;
 9 import cn.itcast.p4.hashset.demo.HashSetDemo;
10
11 /*
12  * 定义功能去除ArrayList中的重复元素
13  */
14 public class ArrayListTest2 {
15
16     public static void main(String[] args) {
17         // TODO Auto-generated method stub
18
19         ArrayList al = new ArrayList();
20         al.add(new Person("list1",21));
21         al.add(new Person("list2",22));
22         al.add(new Person("list3",23));
23         al.add(new Person("list4",24));
24         al.add(new Person("list4",24));
25         al.add(new Person("list4",24));
26
27         System.out.println(al);
28
29         al = getSingleElement(al);
30
31         System.out.println(al);
32
33 //        System.out.println(al.remove(new Person("list2",22)));//remove 也是和equals相关
34
35 //        System.out.println(al);
36
37 //        singleDemo();
38     }
39
40     private static ArrayList getSingleElement_2(ArrayList al) {
41         // TODO Auto-generated method stub
42         return null;
43     }
44
45     /**
46      *
47      */
48     public static void singleDemo() {
49         ArrayList al = new ArrayList();
50         al.add("abc1");
51         al.add("abc2");
52         al.add("abc2");
53         al.add("abc1");
54         al.add("abc");
55         System.out.println(al);
56         al = getSingleElement(al);
57         System.out.println(al);
58
59
60     }
61     public static ArrayList getSingleElement(ArrayList al) {
62         //1，定义一个临时容器
63         ArrayList temp = new ArrayList();
64
65         //2,迭代al集合
66         Iterator it = al.iterator();
67
68         while(it.hasNext()) {
69             Object obj = it.next();
70             //3,判断被迭代到的元素是否在临时容器存在。
71             if (!temp.contains(obj)) {//contains也是依据equals，如果person类equals没有重写，比较的还是地址值
72                 temp.add(obj);
73             }
74         }
75
76         return temp;
77     }
78
79
80
81 }

 1 package cn.itcast.p.bean;
 2
 3 public class Person {
 4     private String name;
 5     private int age;
 6
 7
 8     public Person() {
 9         super();
10         // TODO Auto-generated constructor stub
11     }
12     public Person(String name, int age) {
13         super();
14         this.name = name;
15         this.age = age;
16     }
17
18     @Override
19     public int hashCode() {
20         System.out.println(this+".....hashCode");
21         // TODO Auto-generated method stub
22         return name.hashCode()+age*27;//age后面乘以一个数增大离散程度，减少返回哈希值相等的几率
23                                     //好比张三哈希值20 年龄40  李四哈希值30，年龄30 结果哈希值一样
24                                     //乘一个数后就不一样了离散程度变大了
25
26
27         //return 100;//会比较equals
28     }
29     public boolean equals(Object obj) {
30         //健壮性
31         if (this == obj) {//有可能传入相同的对象，可以先行判断是否为同一对象add(p) add(p)这种传入两次
32             return true;
33         }
34         if (!(obj instanceof Person)) {//判断是否为Person类型，类型不一致也不应该传入
35             throw new ClassCastException("类型错误");
36         }
37
38 //        System.out.println(this+"...equals...."+obj);
39         Person p = (Person)obj;
40
41
42         return this.name.equals(p.name) && this.age == p.age;
43     }
44     public String getName() {
45         return name;
46     }
47     public void setName(String name) {
48         this.name = name;
49     }
50     public int getAge() {
51         return age;
52     }
53     public void setAge(int age) {
54         this.age = age;
55     }
56     //ctrl+alt+s 快捷构造set，get方法 初始化等
57     public String toString() {
58         return name+":"+age;
59     }
60 }

Person