Java集合类详解

package collection;

import org.junit.Test;

import java.util.HashSet;
import java.util.Set;

/**
 * Created by :Infaraway
 * DATE : 2017/3/26
 * Time : 13:18
 * Funtion : 测试HashSet
 *
 * 关于HashSet
 * 1. HashSet是Set的最典型的实现
 * 2. HashSet中不能有重复的元素，判断两个元素相等的标准是equals()方法返回true
 * 3. HashSet根据hashCode()值来存储元素，因此不能保证元素的顺序
 * 4. 如果两个对象通过equals()方法返回true 这两个对象的hashcode值应该是相同的
 * 5. HashSet 是线程不安全的
 */

public class HashSetTest {

    @Test
    public void testAdd(){
        Set set = new HashSet();

        set.add(new Person("AAA",22));
        set.add(new Person("BBB",22));
        set.add(new Person("CCC",27));
        set.add(new Person("DDD",29));
        System.out.println(set.size());

        for (Object person : set) {
            System.out.println(person.toString());
        }

    }

}

 1 package collection;
 2 
 3 /**
 4  * Created by : Zhong
 5  * DATE : 2017/3/2
 6  * Time : 23:06
 7  * Funtion :
 8  */
 9 public class PersonCompare implements Comparable{
10     public String name;
11     public int age;
12     public PersonCompare() {
13     }
14     public PersonCompare(String name, int age) {
15         this.name = name;
16         this.age = age;
17     }
18     public String getName() {
19         return name;
20     }
21     public void setName(String name) {
22         this.name = name;
23     }
24     public int getAge() {
25         return age;
26     }
27     public void setAge(int age) {
28         this.age = age;
29     }
30     @Override
31     public String toString() {
32         return "Person{" +
33                 "name=‘" + name + ‘\‘‘ +
34                 ", age=" + age +
35                 ‘}‘;
36     }
37 
38     @Override
39     public boolean equals(Object o) {
40         if (this == o) return true;
41         if (o == null || getClass() != o.getClass()) return false;
42 
43         PersonCompare person = (PersonCompare) o;
44 
45         if (age != person.age) return false;
46         return name != null ? name.equals(person.name) : person.name == null;
47 
48     }
49     @Override
50     public int hashCode() {
51         int result = name != null ? name.hashCode() : 0;
52         result = 31 * result + age;
53         return result;
54     }
55 
56     @Override
57     public int compareTo(Object o) {
58 
59         if (o instanceof PersonCompare){
60             PersonCompare personCompare = (PersonCompare) o;
61             return this.name.compareTo(personCompare.name);
62         }else{
63             throw new ClassCastException("转换类型失败！");
64         }
65     }
66 }

/**
     * 自然排序情况
     *
     * 默认情况下TreeSet要求集合中的元素必须实现Comparable接口
     * Comparable接口中只有一个方法：
     * public int compareTo(T o)
     *     如果返回0 代表两个元素相等
     *     如果返回正数，代表当前元素大
     *     如果返回负数，代表当前元素小
     * TreeSet 会调用每个元素的compareTo()方法去和集合中的每个已经有的元素比较，进而决定当前元素在集合中的位置
     *
     */
    @Test
    public void testTreeSet(){

        TreeSet treeSet = new TreeSet();
        treeSet.add(new PersonCompare("AAA",16));
        treeSet.add(new PersonCompare("BBB",13));
        treeSet.add(new PersonCompare("CCC",11));
        treeSet.add(new PersonCompare("DDD",15));

        for (Object o : treeSet) {
            System.out.println(o.toString());
        }
    }

/**
     * 定制排序
     *
     */
    @Test
    public void testTreeSet2(){
        //创建comparator接口的实现类对象
        Comparator comparator = new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                if (o1 instanceof Person && o2 instanceof Person){
                    Person p1 = (Person)o1;
                    Person p2 = (Person)o2;
                    return p1.getAge() - p2.getAge();
                }
                throw new ClassCastException("类型转换异常");
            }
        };

        //创建TreeSet对象，传入Comparator接口的实现类对象
        TreeSet treeSet = new TreeSet(comparator);
        treeSet.add(new Person("AAA",16));
        treeSet.add(new Person("BBB",13));
        treeSet.add(new Person("CCC",11));
        treeSet.add(new Person("DDD",15));

        for (Object person : treeSet) {
            System.out.println(person.toString());
        }
    }

 1 @Test
 2     public void testLinkedHashMap(){
 3         Map map = new LinkedHashMap<>();
 4 
 5         map.put("CC", new Person("CC", 18));
 6         map.put("AA", new Person("AA", 10));
 7         map.put("DD", new Person("DD", 12));
 8         map.put("BB", new Person("BB", 16));
 9 
10         /*Iterator it = map.keySet().iterator();
11         while (it.hasNext()){
12             Object key = it.next();
13             Object value = http://www.mamicode.com/map.get(key);":"+value);
15         }
16         System.out.println();*/
17 
18         for (Object key : map.keySet()){
19             Object value = http://www.mamicode.com/map.get(key);":"+value);
21         }
22     }

 1    @Test
 2     public void testTreeMap(){
 3         Map map = new TreeMap<>();
 4 
 5         //这里使用加入Compareable接口的Person类，这样才可以进行排序
 6         map.put(new PersonCompare("CC", 18),"CC");
 7         map.put(new PersonCompare("AA", 10),"AA");
 8         map.put(new PersonCompare("DD", 12),"DD");
 9         map.put(new PersonCompare("BB", 16),"BB");
10 
11         for (Object key : map.keySet()){
12             Object value = http://www.mamicode.com/map.get(key);":"+value);
14         }
15     }

 1 package collection;
 2 
 3 import org.junit.Test;
 4 
 5 import java.util.*;
 6 
 7 /**
 8  * Created by :Infaraway
 9  * DATE : 2017/3/26
10  * Time : 16:39
11  * Funtion :
12  */
13 public class CollectionsTest {
14 
15     @Test
16     public void testList(){
17         List list = new ArrayList<>();
18         list.add(new Person("AAA",16));
19         list.add(new Person("BBB",13));
20         list.add(new Person("CCC",11));
21         list.add(new Person("DDD",15));
22 
23         for (Object o : list) {
24             System.out.println(o.toString());
25         }
26         //按年龄升序排列
27         //实现Comparator类进行排序操作
28         Collections.sort(list, new Comparator() {
29             @Override
30             public int compare(Object o1, Object o2) {
31                 if (o1 instanceof Person && o2 instanceof Person){
32                     Person p1 = (Person)o1;
33                     Person p2 = (Person)o2;
34                     return p1.getAge() - p2.getAge();
35                 }
36                 throw new ClassCastException("类型转换异常");
37             }
38         });
39 
40         System.out.println();
41         for (Object o : list) {
42             System.out.println(o.toString());
43         }
44 
45 
46         //获取list中最小的元素
47         //要求集合中的元素都实现Compareable接口
48         Set set = new HashSet();
49 
50         set.add(new PersonCompare("AAA",20));
51         set.add(new PersonCompare("BBB",34));
52         set.add(new PersonCompare("CCC",27));
53         set.add(new PersonCompare("DDD",29));
54 
55         for (Object person : set) {
56             System.out.println(person.toString());
57         }
58         System.out.println();
59 
60         Object object = Collections.min(set);
61         System.out.println(object.toString());
62     }
63 
64 }