泛型的两个使用练习
- 定义一个Employee类， 该类包含：private成员变量name,age,birthday，其中 birthday 为 MyDate 类的对象； 并为每一个属性定义 getter, setter 方法； 并重写 toString 方法输出 name, age, birthday
MyDate类包含: private成员变量month,day,year；并为每一个属性定义 getter, setter 方法；
创建该类的 5 个对象，并把这些对象放入 TreeSet 集合中（TreeSet 需使用泛型来定义）， 分别按以下两种方式对集合中的元素进行排序，并遍历输出：
1). 使Employee 继承 Comparable 接口，并按 name 排序 2). 创建 TreeSet 时传入 Comparator对象，按生日日期的先后排序。
package fourteendemo;
/*
* MyDate类包含:
private成员变量month,day,year；并为每一个属性定义 getter, setter 方法；
*/
public class MyDate {
private int day;
private int month;
private int year;
public int getDay() {
return day;
}
public void setDay(int day) {
this.day = day;
}
public int getMonth() {
return month;
}
public void setMonth(int month) {
this.month = month;
}
public int getYear() {
return year;
}
public void setYear(int year) {
this.year = year;
}
public MyDate(int day, int month, int year) {
super();
this.day = day;
this.month = month;
this.year = year;
}
@Override
public String toString() {
return "MyDate [day=" + day + ", month=" + month + ", year=" + year
+ "]";
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + day;
result = prime * result + month;
result = prime * result + year;
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
MyDate other = (MyDate) obj;
if (day != other.day)
return false;
if (month != other.month)
return false;
if (year != other.year)
return false;
return true;
}
}
package fourteendemo;
/*
* 定义一个Employee类，
该类包含：private成员变量name,age,birthday，其中 birthday 为 MyDate 类的对象；
并为每一个属性定义 getter, setter 方法；
并重写 toString 方法输出 name, age, birthday
*/
public class Employee implements Comparable{
private String name;
private int age;
private MyDate birthday;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public MyDate getBirthday() {
return birthday;
}
public void setBirthday(MyDate birthday) {
this.birthday = birthday;
}
public Employee(String name, int age, MyDate birthday) {
super();
this.name = name;
this.age = age;
this.birthday = birthday;
}
@Override
public String toString() {
return "Employee [name=" + name + ", age=" + age + ", birthday="
+ birthday + "]";
}
@Override
public int compareTo(Object o) {
if(o instanceof Employee){
Employee e = (Employee)o;
return this.name.compareTo(e.name);
}
return 0;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + age;
result = prime * result
+ ((birthday == null) ? 0 : birthday.hashCode());
result = prime * result + ((name == null) ? 0 : name.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 (age != other.age)
return false;
if (birthday == null) {
if (other.birthday != null)
return false;
} else if (!birthday.equals(other.birthday))
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}
}
package fourteendemo;
/*
* 定义一个Employee类，
该类包含：private成员变量name,age,birthday，其中 birthday 为 MyDate 类的对象；
并为每一个属性定义 getter, setter 方法；
并重写 toString 方法输出 name, age, birthday
*/
public class Employee1 {
private String name;
private int age;
private MyDate birthday;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public MyDate getBirthday() {
return birthday;
}
public void setBirthday(MyDate birthday) {
this.birthday = birthday;
}
public Employee1(String name, int age, MyDate birthday) {
super();
this.name = name;
this.age = age;
this.birthday = birthday;
}
@Override
public String toString() {
return "Employee [name=" + name + ", age=" + age + ", birthday="
+ birthday + "]";
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + age;
result = prime * result
+ ((birthday == null) ? 0 : birthday.hashCode());
result = prime * result + ((name == null) ? 0 : name.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;
Employee1 other = (Employee1) obj;
if (age != other.age)
return false;
if (birthday == null) {
if (other.birthday != null)
return false;
} else if (!birthday.equals(other.birthday))
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}
}
package fourteendemo;
import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;
import org.junit.Test;
/*
* 创建该类的 5 个对象，并把这些对象放入 TreeSet 集合中（下一章：TreeSet 需使用泛型来定义）
分别按以下两种方式对集合中的元素进行排序，并遍历输出：
1). 使Employee 实现 Comparable 接口，并按 name 排序
2). 创建 TreeSet 时传入 Comparator对象，按生日日期的先后排序。
提示：Employee类是否需要重写equals()方法？MyDate类呢？
*/
public class TestEmployee {
//定制排序：创建 TreeSet 时传入 Comparator对象，按生日日期的先后排序。
@Test
public void test2(){
Comparator com = new Comparator(){
@Override
public int compare(Object o1, Object o2) {
if(o1 instanceof Employee1 && o2 instanceof Employee1){
Employee1 e1 = (Employee1)o1;
Employee1 e2 = (Employee1)o2;
MyDate birth1 = e1.getBirthday();
MyDate birth2 = e2.getBirthday();
if(birth1.getYear() != birth2.getYear()){
return birth1.getYear() - birth2.getYear();
}else{
if(birth1.getMonth() != birth2.getMonth()){
return birth1.getMonth() - birth2.getMonth();
}else{
return birth1.getDay() - birth2.getDay();
}
}
}
return 0;
}
};
TreeSet<Employee1> set = new TreeSet<>(com);
Employee1 e1 = new Employee1("刘德华", 55, new MyDate(4, 12, 1976));
Employee1 e2 = new Employee1("郭富城", 43, new MyDate(7, 3, 1954));
Employee1 e3 = new Employee1("张学友", 33, new MyDate(9, 12, 1954));
Employee1 e4 = new Employee1("黎明", 54, new MyDate(12, 3, 1954));
Employee1 e5 = new Employee1("李敏镐", 65, new MyDate(4, 21, 1945));
set.add(e1);
set.add(e2);
set.add(e3);
set.add(e4);
set.add(e5);
Iterator<Employee1> i = set.iterator();
while(i.hasNext()){
System.out.println(i.next());
}
}
//自然排序： 使Employee 实现 Comparable 接口，并按 name 排序
@Test
public void test1(){
Employee e1 = new Employee("刘德华", 55, new MyDate(4, 12, 1976));
Employee e2 = new Employee("郭富城", 43, new MyDate(7, 3, 1965));
Employee e3 = new Employee("张学友", 33, new MyDate(9, 12, 1954));
Employee e4 = new Employee("黎明", 54, new MyDate(12, 2, 1967));
Employee e5 = new Employee("李敏镐", 65, new MyDate(4, 21, 1945));
// Employee e6 = new Employee("李敏镐", 63, new MyDate(4, 21, 1945));
TreeSet<Employee> set = new TreeSet<>();
set.add(e1);
set.add(e2);
set.add(e3);
set.add(e4);
set.add(e5);
// set.add(e6);
Iterator<Employee> i = set.iterator();
while(i.hasNext()){
System.out.println(i.next());
}
}
}
- 定义个泛型类 DAO
，在其中定义一个Map 成员变量，Map 的键为 String 类型，值为 T 类型。
分别创建以下方法：
public void save(String id,T entity)： 保存 T 类型的对象到 Map 成员变量中
T get(String id)：从 map 中获取 id 对应的对象
void update(String id,T entity)：替换 map 中key为id的内容,改为 entity 对象
List
定义一个 User 类： 该类包含：private成员变量（int类型） id，age；（String 类型）name。
创建 DAO 类的对象， 分别调用其 save、get、update、list、delete 方法来操作 User 对象， 使用 Junit 单元测试类进行测试。
package fourteendemo1;
/*
* 定义一个 User 类：
该类包含：private成员变量（int类型） id，age；（String 类型）name。
*/
public class User {
private int id;
private int age;
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public User(int id, int age, String name) {
super();
this.id = id;
this.age = age;
this.name = name;
}
@Override
public String toString() {
return "User [id=" + id + ", age=" + age + ", name=" + name + "]";
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + age;
result = prime * result + id;
result = prime * result + ((name == null) ? 0 : name.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;
User other = (User) obj;
if (age != other.age)
return false;
if (id != other.id)
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}
}
package fourteendemo1;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/*
* 定义个泛型类 DAO<T>，在其中定义一个Map 成员变量，Map 的键为 String 类型，值为 T 类型。
分别创建以下方法：
public void save(String id,T entity)： 保存 T 类型的对象到 Map 成员变量中
T get(String id)：从 map 中获取 id 对应的对象
void update(String id,T entity)：替换 map 中key为id的内容,改为 entity 对象
List<T> list()：返回 map 中存放的所有 T 对象
void delete(String id)：删除指定 id 对象
*/
public class DAO<T> {
Map<String,T> map;
public void delete(String id){
map.remove(id);
}
public List<T> list(){
List<T> list = new ArrayList<T>();
for(String s : map.keySet()){
list.add(map.get(s));
}
return list;
}
public void update(String id,T entity){
//map.remove(id);
map.put(id, entity);
}
public T get(String id){
return map.get(id);
}
public void save(String id,T entity){
map.put(id, entity);
}
}
package fourteendemo1;
import java.util.HashMap;
import java.util.List;
/*
* 创建 DAO 类的对象， 分别调用其 save、get、update、list、delete 方法来操作 User 对象，
使用 Junit 单元测试类进行测试。
*/
public class TestDAO {
public static void main(String[] args) {
DAO<User> dao = new DAO<User>();
dao.map = new HashMap<String,User>();
dao.save("1001", new User(1, 32, "梁朝伟"));
dao.save("1002", new User(2,34,"汤唯"));
dao.save("1003", new User(3,23,"刘嘉玲"));
User u = dao.get("1002");//把1002的数据传给 u
System.out.println(u);
dao.update("1002", new User(4,45,"成龙"));//替换1002的数据
dao.delete("1003");//删除1003 的数据
List<User> list = dao.list();
System.out.println(list);
}
}
韧桂 2020-01-03