HashMap存储自定义对象
将学生对象和学生的归属地通过键与值存储到map集合中。
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import java.util.HashMap;
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import java.util.Iterator;
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import java.util.Set;
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class Student {
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String name;
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int age;
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public Student(String name,int age){
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super();
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this.name=name;
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this.age=age;
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}
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public String getName(){
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return name;
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}
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public void setName(String name){
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this.name=name;
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}
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public int getAge(){
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return age;
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}
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public void setAge(int age){
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this.age=age;
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}
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}
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public
class HashMapDemo{
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public static void main(String[] args){
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HashMap
hm=
new HashMap();
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hm.put(
new Student(
“lisi”,
38),
“北京”);
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hm.put(
new Student(
“zhaosi”,
34),
“上海”);
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hm.put(
new Student(
“xiaoqiang”,
31),
“沈阳”);
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hm.put(
new Student(
“wangcai”,
28),
“大连”);
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hm.put(
new Student(
“zhaosi”,
34),
“铁岭”);
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Set
keySet=hm.keySet();
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Iterator
it=keySet.iterator();
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while(it.hasNext()){
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Student key=it.next();
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String value=hm.get(key);
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System.out.println(key.getName()+
“:”+key.getAge()+
“…”+value);
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}
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}
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}
当键一样时，其值并没有被覆盖，所以要判断键是否相同，HashMap需要定义hashCode和equals方法，在Student类中要复写方法：
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import java.util.HashMap;
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import java.util.Iterator;
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import java.util.Set;
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class Student {
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String name;
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int age;
-
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public Student(String name,int age){
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super();
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this.name=name;
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this.age=age;
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}
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public String getName(){
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return name;
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}
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public void setName(String name){
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this.name=name;
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}
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public int getAge(){
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return age;
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}
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public void setAge(int age){
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this.age=age;
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}
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public int hashCode(){
//复写hashCode()
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return name.hashCode()+age;
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}
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public boolean equals(Object obj){
//复写equals
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if(
this==obj)
return
true;
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if(!(obj
instanceof Student))
throw
new ClassCastException(
"类型错误");
//输入类型错误
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Student p = (Student)obj;
//强制转换
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return
this.name.equals(p.name) &&
this.age==p.age;
//说明姓名和年龄相同则为同一元素
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}
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}
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public
class HashMapDemo{
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public static void main(String[] args){
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HashMap
hm=
new HashMap();
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hm.put(
new Student(
"lisi",
38),
"北京");
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hm.put(
new Student(
"zhaosi",
34),
"上海");
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hm.put(
new Student(
"xiaoqiang",
31),
"沈阳");
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hm.put(
new Student(
"wangcai",
28),
"大连");
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hm.put(
new Student(
"zhaosi",
34),
"铁岭");
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Set
keySet=hm.keySet();
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Iterator
it=keySet.iterator();
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//以下被注释的代码可以替换上面两句:
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//Iterator
it=hm.keySet().iterator();
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while(it.hasNext()){
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Student key=it.next();
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String value=hm.get(key);
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System.out.println(key.getName()+
":"+key.getAge()+
"..."+value);
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}
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}
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}
