JAVA学习--集合Map的使用

* Map接口
 *         |-----HashMap:Map的主要实现类
 *         |-----LinkedHashMap:使用链表维护添加进Map中的顺序。故遍历Map时，是按添加的顺序遍历的。
 *         |-----TreeMap:按照添加进Map中的元素的key的指定属性进行排序。要求：key必须是同一个类的对象！
 *                 针对key：自然排序   vs 定制排序
 *         |-----Hashtable:古老的实现类，线程安全，不建议使用。
 *             |----Properties:常用来处理属性文件。键和值都为String类型的



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     Object put(Object key,Object value):向Map中添加一个元素
      Object remove(Object key):按照指定的key删除此key-value
      void putAll(Map t)
      void clear():清空
      Object get(Object key)：获取指定key的value值。若无此key，则返回null
      boolean containsKey(Object  key)
      boolean containsValue(Object value)
      int size():返回集合的长度
      boolean isEmpty() boolean equals(Object obj)
      HashMap： 1.key是用Set来存放的，不可重复。value是用Collection来存放的，可重复
     一个key-value对，是一个Entry。所有的Entry是用Set存放的，也是不可重复的。
     2.向HashMap中添加元素时，会调用key所在类的equals()方法，判断两个key是否相同。若相同 则只能添加 进后添加的那个元素。

 

 1 @Test

 2     public void test1() {

 3         Map map = new HashMap();

 4         map.put("AA", 213);

 5         map.put("BB", 456);

 6         map.put("BB", 45);

 7         map.put(123, "CC");

 8         map.put(null, null);

 9         map.put(new Person("DD", 23), 89);

10         map.put(new Person("DD", 23), 87);

11         System.out.println(map.size());

12         System.out.println(map);

13         map.remove("BB");

14         System.out.println(map);

15         Object value = map.get(1234);

16         System.out.println(value);

17     }

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    * 如何遍历Map Set keySet() Collection values() Set entrySet()

 

 1 @Test

 2     public void test2() {

 3         Map map = new HashMap();

 4         map.put("AA", 213);

 5         map.put("BB", 45);

 6         map.put(123, "CC");

 7         map.put(null, null);

 8         map.put(new Person("DD", 23), 89);

 9 

10         // 1.遍历key集。

11         Set set = map.keySet();

12         for (Object obj : set) {

13             System.out.println(obj);

14         }

15         // 2.遍历value集

16         Collection values = map.values();

17         Iterator i = values.iterator();

18         while (i.hasNext()) {

19             System.out.println(i.next());

20         }

21         // 3.如何遍历key-value对。

22         // 方式一：

23         Set set1 = map.keySet();

24         for (Object obj : set1) {

25             System.out.println(obj + "----->" + map.get(obj));

26         }

27         // 方式二：

28         Set set2 = map.entrySet();

29         for (Object obj : set2) {

30             Map.Entry entry = (Map.Entry) obj;

31             // System.out.println(entry.getKey() + "---->" + entry.getValue());

32             System.out.println(entry);

33         }

34     }

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**LinkedHashMap用法

 

 1 @Test

 2     public void test3() {

 3         Map map = new LinkedHashMap();

 4         map.put("AA", 213);

 5         map.put("BB", 45);

 6         map.put(123, "CC");

 7         map.put(null, null);

 8         map.put(new Person("DD", 23), 89);

 9 

10         Set set1 = map.keySet();

11         for (Object obj : set1) {

12             System.out.println(obj + "----->" + map.get(obj));

13         }

14     }

 1 // 自然排序

 2     @Test

 3     public void test4() {

 4         Map map = new TreeMap();

 5         map.put(new Person("AA", 23), 89);

 6         map.put(new Person("MM", 22), 79);

 7         map.put(new Person("GG", 23), 99);

 8         map.put(new Person("JJ", 13), 69);

 9 

10         Set set1 = map.keySet();

11         for (Object obj : set1) {

12             System.out.println(obj + "----->" + map.get(obj));

13         }

14     }

 1  // 定制排序

 2     @Test

 3     public void test5() {

 4         Comparator com = new Comparator() {

 5             public int compare(Object o1, Object o2) {

 6                 if (o1 instanceof Customer && o2 instanceof Customer) {

 7                     Customer c1 = (Customer) o1;

 8                     Customer c2 = (Customer) o2;

 9                     int i = c1.getId().compareTo(c2.getId());

10                     if (i == 0) {

11                         return c1.getName().compareTo(c2.getName());

12                     }

13                     return i;

14                 }

15                 return 0;

16             }

17         };

18         TreeMap map = new TreeMap(com);

19         map.put(new Customer("AA", 1001), 87);

20         map.put(new Customer("CC", 1001), 67);

21         map.put(new Customer("MM", 1004), 77);

22         map.put(new Customer("GG", 1002), 97);

23        

24         Set set1 = map.keySet();

25         for (Object obj : set1) {

26             System.out.println(obj + "----->" + map.get(obj));

27         }

28     }

-----------------------------------------------------------------------------------以下为填充集合的类

  1 class Customer {

  2  

  3    private String name;

  4     private Integer id;

  5     public String getName() {

  6         return name;

  7     }

  8     public void setName(String name) {

  9         this.name = name;

 10     }

 11     public Integer getId() {

 12         return id;

 13     }

 14     public void setId(Integer id) {

 15         this.id = id;

 16     }

 17     public Customer(String name, Integer id) {

 18         super();

 19         this.name = name;

 20         this.id = id;

 21     }

 22     public Customer() {

 23         super();

 24     }

 25     @Override

 26     public String toString() {

 27         return "Customer [name=" + name + ", id=" + id + "]";

 28     }

 29     @Override

 30     public int hashCode() {

 31         final int prime = 31;

 32         int result = 1;

 33         result = prime * result + ((id == null) ? 0 : id.hashCode());

 34         result = prime * result + ((name == null) ? 0 : name.hashCode());

 35         return result;

 36     }

 37     @Override

 38     public boolean equals(Object obj) {

 39         if (this == obj)

 40             return true;

 41         if (obj == null)

 42             return false;

 43         if (getClass() != obj.getClass())

 44             return false;

 45         Customer other = (Customer) obj;

 46         if (id == null) {

 47             if (other.id != null)

 48                 return false;

 49         } else if (!id.equals(other.id))

 50             return false;

 51         if (name == null) {

 52             if (other.name != null)

 53                 return false;

 54         } else if (!name.equals(other.name))

 55             return false;

 56         return true;

 57     }

 58    

 59 }

 60 

 61 class Person implements Comparable{

 62     private String name;

 63     private Integer age;

 64     public String getName() {

 65         return name;

 66     }

 67     public void setName(String name) {

 68         this.name = name;

 69     }

 70     public Integer getAge() {

 71         return age;

 72     }

 73     public void setAge(Integer age) {

 74         this.age = age;

 75     }

 76     public Person() {

 77         super();

 78     }

 79     public Person(String name, Integer age) {

 80         super();

 81         this.name = name;

 82         this.age = age;

 83     }

 84     @Override

 85     public String toString() {

 86         return "Person [name=" + name + ", age=" + age + "]";

 87     }

 88     //static int init = 1000;

 89     @Override

 90     public int hashCode() {//return age.hashCode() + name.hashCode();没下述的健壮性好。

 91         final int prime = 31;

 92         int result = 1;

 93         result = prime * result + ((age == null) ? 0 : age.hashCode());

 94         result = prime * result + ((name == null) ? 0 : name.hashCode());

 95         return result;

 96         //return init++;//不能这样用

 97     }

 98     @Override

 99     public boolean equals(Object obj) {

100         if (this == obj)

101             return true;

102         if (obj == null)

103             return false;

104         if (getClass() != obj.getClass())

105             return false;

106         Person other = (Person) obj;

107         if (age == null) {

108             if (other.age != null)

109                 return false;

110         } else if (!age.equals(other.age))

111             return false;

112         if (name == null) {

113             if (other.name != null)

114                 return false;

115         } else if (!name.equals(other.name))

116             return false;

117         return true;

118     }

119     //当向TreeSet中添加Person类的对象时，依据此方法，确定按照哪个属性排列。

120     @Override

121     public int compareTo(Object o) {

122         if(o instanceof Person){

123             Person p = (Person)o;

124             //return this.name.compareTo(p.name);

125             //return -this.age.compareTo(p.age);

126             int i = this.age.compareTo(p.age);

127             if(i == 0){

128                 return this.name.compareTo(p.name);

129             }else{

130                 return i;

131             }

132         }

133         return 0;

134     }

135    

136 }