java练习

学习Java，可考取Oracle的Java SE或EE认证 #生活技巧# #工作学习技巧# #技能培训认证#

1. 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 year,month,day ；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（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。

public class Employee implements Comparable<Employee>{

private String name;

private int age;

private MyDate birthday;

public Employee(String name, int age, MyDate birthday) {

this.name = name;

this.age = age;

this.birthday = birthday;

}

public Employee() {

}

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;

}

@Override

public String toString() {

return "Employee{" + "name='" + name + '\'' + ", age=" + age + ", birthday=" + birthday + '}';

}

@Override

public int compareTo(Employee o) {

return this.name.compareTo(o.name);

}

}

public class MyDate implements Comparable<MyDate>{

private int year;

private int month;

private int day;

public MyDate(int year, int month, int day) {

this.year = year;

this.month = month;

this.day = day;

}

public MyDate() {

}

public int getYear() {

return year;

}

public void setYear(int year) {

this.year = year;

}

public int getMonth() {

return month;

}

public void setMonth(int month) {

this.month = month;

}

public int getDay() {

return day;

}

public void setDay(int day) {

this.day = day;

}

@Override

public String toString() {

return "MyDate{" + "year=" + year + ", month=" + month + ", day=" + day + '}';

}

@Override

public int compareTo(MyDate m) {

int minusYear = this.getYear() - m.getYear();

if(minusYear != 0){

return minusYear;

}

int minusMonth = this.getMonth() - m.getMonth();

if(minusMonth != 0){

return minusMonth;

}

return this.getDay() - m.getDay();

}

}

import org.junit.Test;

import java.util.Comparator;

import java.util.Iterator;

import java.util.TreeSet;

public class MyTest {

@Test

public void test1(){

TreeSet<Employee> set = new TreeSet<Employee>();

Employee e1 = new Employee("liudehua",55,new MyDate(1965,5,4));

Employee e2 = new Employee("zhangxueyou",43,new MyDate(1987,5,4));

Employee e3 = new Employee("guofucheng",44,new MyDate(1987,5,9));

Employee e4 = new Employee("liming",51,new MyDate(1954,8,12));

Employee e5 = new Employee("liangzhaowei",21,new MyDate(1978,12,4));

set.add(e1);

set.add(e2);

set.add(e3);

set.add(e4);

set.add(e5);

Iterator<Employee> iterator = set.iterator();

while (iterator.hasNext()){

Employee employee = iterator.next();

System.out.println(employee);

}

//Employee{name='guofucheng', age=44, birthday=MyDate{year=1987, month=5, day=9}}

//Employee{name='liangzhaowei', age=21, birthday=MyDate{year=1978, month=12, day=4}}

//Employee{name='liming', age=51, birthday=MyDate{year=1954, month=8, day=12}}

//Employee{name='liudehua', age=55, birthday=MyDate{year=1965, month=5, day=4}}

//Employee{name='zhangxueyou', age=43, birthday=MyDate{year=1987, month=5, day=4}}

}

@Test

public void test2(){

TreeSet<Employee> set = new TreeSet(new Comparator<Employee>() {

@Override

public int compare(Employee o1, Employee o2) {

MyDate b1 = o1.getBirthday();

MyDate b2 = o2.getBirthday();

return b1.compareTo(b2);

}

});

Employee e1 = new Employee("liudehua",55,new MyDate(1965,5,4));

Employee e2 = new Employee("zhangxueyou",43,new MyDate(1987,5,4));

Employee e3 = new Employee("guofucheng",44,new MyDate(1987,5,9));

Employee e4 = new Employee("liming",51,new MyDate(1954,8,12));

Employee e5 = new Employee("liangzhaowei",21,new MyDate(1978,12,4));

set.add(e1);

set.add(e2);

set.add(e3);

set.add(e4);

set.add(e5);

Iterator<Employee> iterator = set.iterator();

while (iterator.hasNext()){

System.out.println(iterator.next());

}

//Employee{name='liming', age=51, birthday=MyDate{year=1954, month=8, day=12}}

//Employee{name='liudehua', age=55, birthday=MyDate{year=1965, month=5, day=4}}

//Employee{name='liangzhaowei', age=21, birthday=MyDate{year=1978, month=12, day=4}}

//Employee{name='zhangxueyou', age=43, birthday=MyDate{year=1987, month=5, day=4}}

//Employee{name='guofucheng', age=44, birthday=MyDate{year=1987, month=5, day=9}}

}

}

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

public T get(String id) ：从 map 中获取 id 对应的对象

public void update(String id,T entity) ：替换 map 中 key 为 id 的内容 ,

改为 entity 对象

public List<T> list() ：返回 map 中存放的所有 T 对象

public void delete(String id) ：删除指定 id 对象

定义一个 User 类：

该类包含： private 成员变量（ int 类型）

id ， age ；（ String 类型） name 。

定义一个测试类：

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。

import java.util.*;

public class DAO<T> {

private Map<String,T> map = new HashMap<String,T>();

//保存 T 类型的对象到 Map 成员变量中

public void save(String id,T entity){

map.put(id,entity);

}

//从 map 中获取 id 对应的对象

public T get(String id){

return map.get(id);

}

//替换 map 中key为id的内容,改为 entity 对象

public void update(String id,T entity){

if(map.containsKey(id)){

map.put(id,entity);

}

}

//返回 map 中存放的所有 T 对象

public List<T> list(){

//正确的：

ArrayList<T> list = new ArrayList<>();

Collection<T> values = map.values();

for(T t : values){

list.add(t);

}

return list;

}

//删除指定 id 对象

public void delete(String id){

map.remove(id);

}

}

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) {

this.id = id;

this.age = age;

this.name = name;

}

public User() {

}

@Override

public String toString() {

return "User{" +

"id=" + id +

", age=" + age +

", name='" + name + '\'' +

'}';

}

}

import org.junit.Test;

import java.util.List;

public class DAOtest {

@Test

public void test(){

DAO<User> dao=new DAO<User>();

dao.save("1001",new User(1001,34,"周杰伦"));

dao.save("1002",new User(1002,20,"昆凌"));

dao.save("1003",new User(1003,25,"蔡依林"));

dao.update("1003",new User(1003,30,"方文山"));

List<User> list = dao.list();

list.forEach(System.out::println);

}

}

User{id=1003, age=30, name='方文山'}

User{id=1002, age=20, name='昆凌'}

User{id=1001, age=34, name='周杰伦'}

网址：java练习 https://www.yuejiaxmz.com/news/view/733166

相关内容

JAVA学习五
2020年Java实习：实战攻略与职场生存指南
java I/O学习（二）
10年Java面试总结：Java程序员面试必备的面试技巧
Java技能提升指南
Java并发编程深入学习指南
Java基于Java的运动健身平台(源码+mysql+文档)
java ip地址 split
java软件工程师
Java 零基础入门学习（小白也能看懂！）

随便看看