HashMap類とLinked HashMap類
42295 ワード
HashMap類とLinked HashMap類
HashMap類
特徴:.底のデータ構造は、ハッシュテーブル である..要素無秩序、唯一の .データ構造はキーに対してのみ有効であり、値に関係なく .要素に固有の依存性を保証するhashCodeとequals方法 .キーがシステムクラスの場合、hashCodeとequalsを書き換える方法が一般的です.もしキーがカスタムクラスの場合、自分で書き換える必要があります.
最下層hashcodeとequals
1.下のデータ構造はチェーンテーブル＋ハッシュテーブルである.
2.チェーンテーブルは元素の秩序を保証し、ハッシュ表は要素の一意性を保証する.
HashMap類
特徴:
最下層hashcodeとequals
public final int hashCode() {
return Objects.hashCode(key) ^ Objects.hashCode(value);
}
public final boolean equals(Object o) {
if (o == this)
return true;
if (o instanceof Map.Entry) {
Map.Entry<?,?> e = (Map.Entry<?,?>)o;
if (Objects.equals(key, e.getKey()) &&
Objects.equals(value, e.getValue()))
return true;
}
return false;
}
```java
```java
public class HashMapDemo01 {
public static void main(String[] args) {
HashMap<Employee, String> hm = new HashMap<>();
hm.put(new Employee("1001", " 1", 2600.0), " 1");
hm.put(new Employee("1002", " 2", 2700.0), " 2");
hm.put(new Employee("1002", " 2", 2700.0), " 2");
hm.put(new Employee("1003", " 3", 2800.0), " 3");
hm.put(new Employee("1003", " 3", 2800.0), " 3");
for(Employee e : hm.keySet()) {
String value = hm.get(e);
System.out.println(e + "=" + value);
}
}
}
public class Employee {
private String id;
private String name;
private Double salary;
public Employee() {
super();
}
public Employee(String id, String name, Double salary) {
super();
this.id = id;
this.name = name;
this.salary = salary;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Double getSalary() {
return salary;
}
public void setSalary(Double salary) {
this.salary = salary;
}
@Override
public String toString() {
return "Employee [id=" + id + ", name=" + name + ", salary=" + salary + "]";
}
@Override
public int hashCode() {// ,
final int prime = 31;
int result = 1;
result = prime * result + ((id == null) ? 0 : id.hashCode());
result = prime * result + ((name == null) ? 0 : name.hashCode());
result = prime * result + ((salary == null) ? 0 : salary.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {// ,
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Employee other = (Employee) obj;
if (id == null) {
if (other.id != null)
return false;
} else if (!id.equals(other.id))
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
if (salary == null) {
if (other.salary != null)
return false;
} else if (!salary.equals(other.salary))
return false;
return true;
}
}
1.下のデータ構造はチェーンテーブル＋ハッシュテーブルである.
2.チェーンテーブルは元素の秩序を保証し、ハッシュ表は要素の一意性を保証する.
public class LinkedHashMapDemo01 {
public static void main(String[] args) {
LinkedHashMap<Employee, String> hm = new LinkedHashMap<>();
hm.put(new Employee("1001", " 1", 2600.0), " 1");
hm.put(new Employee("1002", " 2", 2700.0), " 2");
hm.put(new Employee("1002", " 2", 2700.0), " 2");
hm.put(new Employee("1003", " 3", 2800.0), " 3");
hm.put(new Employee("1003", " 3", 2800.0), " 3");
for(Employee e : hm.keySet()) {
String value = hm.get(e);
System.out.println(e + "=" + value);
}
}
}
public class Employee {
private String id;
private String name;
private Double salary;
public Employee() {
super();
}
public Employee(String id, String name, Double salary) {
super();
this.id = id;
this.name = name;
this.salary = salary;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Double getSalary() {
return salary;
}
public void setSalary(Double salary) {
this.salary = salary;
}
@Override
public String toString() {
return "Employee [id=" + id + ", name=" + name + ", salary=" + salary + "]";
}
@Override
public int hashCode() {// ,
final int prime = 31;
int result = 1;
result = prime * result + ((id == null) ? 0 : id.hashCode());
result = prime * result + ((name == null) ? 0 : name.hashCode());
result = prime * result + ((salary == null) ? 0 : salary.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {// ,
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Employee other = (Employee) obj;
if (id == null) {
if (other.id != null)
return false;
} else if (!id.equals(other.id))
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
if (salary == null) {
if (other.salary != null)
return false;
} else if (!salary.equals(other.salary))
return false;
return true;
}
}