范例：Map中的key不允許重復，重復就是覆蓋

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[java]?view plaincopy

package?org.lxh.demo13.mapdemo;????

import?java.util.HashMap;????

import?java.util.Iterator;????

import?java.util.Map;????

import?java.util.Set;????

class?Person?{????????????????????????????????

//?定義Person類????

????private?String?name;?????????????????????

//?定義name屬性????

????private?int?age;??????????????????????????

//?定義age屬性????

????public?Person(String?name,?int?age)?{?????

//?通過構造方法為屬性賦值????

????????this.name?=?name;?????????????????????

//?為name屬性賦值????

????????this.age?=?age;???????????????????????

//?為age屬性賦值????

????}????

????public?boolean?equals(Object?obj)?{??????

//?覆寫equals()方法????

????????if?(this?==?obj)?{????????????????????

//?判斷地址是否相等????

????????????return?true;??????????????????????

//?返回true表示同一對象????

????????}????

????????if?(!(obj?instanceof?Person))?{???????

//?傳遞進來的不是本類的對象????

????????????return?false;?????????????????????

//?返回false表示不是同一對象????

????????}????

????????Person?p?=?(Person)?obj;??????????????

//?進行向下轉型????

????????if?(this.name.equals(p.name)?&&??

this.age?==?p.age)?{????

????????????return?true?;?????????????????????

//?屬性依次比較，相等返回true????

????????}else{????

????????????return?false?;????????????????????

//?屬性內容不相等，返回false????

????????}????

????}????

????public?int?hashCode(){??????????????????????

//?覆寫hashCode()方法????

????????return?this.name.hashCode()?*?this.age?;????

//?計算公式????

????}????

????public?String?toString()?{??????????????????????

//?覆寫toString()方法????

????????return?"姓名："?+?this.name?+?"；年齡："???

+?this.age;???//?返回信息????

????}????

}?????

public?class?IdentityHashMapDemo01?{????

????public?static?void?main(String[]?args)?{????

????????Map<Person,?String>?map?=?null;??????????????

//?聲明Map對象，指定????

泛型類型????

????????map?=?new?HashMap<Person,?String>();???????????

//?實例化Map對象????

????????map.put(new?Person("張三",?30),?"zhangsan_1");????

//?增加內容????

????????map.put(new?Person("張三",?30),?"zhangsan_2");?????

//?增加內容，key重復????

????????map.put(new?Person("李四",?31),?"lisi");???????

//?增加內容????

????????Set<Map.Entry<Person,?String>>?allSet?=?null;????

//?聲明一個Set集合????

????????allSet?=?map.entrySet();????????????????????

//?將Map接口實例變為????

Set接口實例????

????????Iterator<Map.Entry<Person,?String>>???

iter?=?null;????//?聲明Iterator????

對象????

????????iter?=?allSet.iterator();????????????????

//?實例化Iterator????

對象????

????????while?(iter.hasNext())?{?????????????????

//?迭代輸出????

????????????Map.Entry<Person,?String>?me?=???

iter.next();//?每個對象都是Map.?????

Entry實例????

????????????System.out.println(me.getKey()?????

????????????????????+?"?-->?"?+?me.getValue());????

//?輸出key和value????

????????}????

????}????

}???

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程序運行結果：

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姓名：李四；年齡：31?-->?lisi????

姓名：張三；年齡：30?-->?zhangsan_2???

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從程序的運行結果中可以發現，第二個內容覆蓋了第一個內容，所以此時可以使用Identity HashMap。使用此類時只要地址不相等（key1！=key2），就表示不是重復的key，可以添加到集合中。

范例：使用IdentityHashMap修改程序

[java]?view plaincopy

package?org.lxh.demo13.mapdemo;????

import?java.util.IdentityHashMap;????

import?java.util.Iterator;????

import?java.util.Map;????

import?java.util.Set;????

class?Person?{????

????//?此類與之前定義一樣，此處不再列出????

}????

public?class?IdentityHashMapDemo02?{????

????public?static?void?main(String[]?args)?{????

????????Map<Person,?String>?map?=?null;??????????

//?聲明Map對象，指定????

泛型類型????

????????map?=?new?IdentityHashMap<Person,?String>();???

//?實例化Map對象????

????????map.put(new?Person("張三",?30),?"zhangsan_1");???

//?增加內容????

????????map.put(new?Person("張三",?30),?"zhangsan_2");????

//?增加內容，key重復????

????????map.put(new?Person("李四",?31),?"lisi");??????

//?增加內容????

????????Set<Map.Entry<Person,?String>>?allSet?=???

null;???//?聲明一個Set集合????

????????allSet?=?map.entrySet();?????????????????

//?將Map接口實例變為????

Set接口實例????

????????Iterator<Map.Entry<Person,?String>>???

iter?=?null;//?聲明Iterator對象????

????????iter?=?allSet.iterator();??????????????

//?實例化Iterator????

對象????

????????while?(iter.hasNext())?{?????????????????

//?迭代輸出????

????????????Map.Entry<Person,?String>?me?=???

iter.next();//?每個對象都是Map.????

Entry實例????

????????????System.out.println(me.getKey()?????

????????????????????+?"?-->?"?+?me.getValue());????

//?輸出key和value????

????????}????

????}????

}???

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程序運行結果：

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姓名：張三；年齡：30?-->?zhangsan_2????

姓名：張三；年齡：30?-->?zhangsan_1????

姓名：李四；年齡：31?-->?lisi???

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從程序的運行結果中可以發現，現在的key允許重復，只要兩個對象的地址不相等即可。

總結

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