Java编程练习题：面向对象练习

目录

1. (LeetCode 第169题)给定一个大小为 n 的数组 nums ，返回其中的多数元素。多数元素是指在数组中出现次数大于 n/2 的元素。

2. 综合案例（用户博客管理系统）

3. （抽象类）定义一个抽象的"Role"类 有姓名 年龄 性别等成员变量

4. （抽象类）品尝饮料

1. (LeetCode 第169题)给定一个大小为 n 的数组 nums ，返回其中的多数元素。多数元素是指在数组中出现次数大于 n/2 的元素。

例如：[1,1,1,1,2,3,3]，多数元素为1

方法1：排序数组，找最中间的数

如果将数组 nums 中的所有元素按照单调递增或单调递减的顺序排序，那么下标为nums.lenght/2的元素（下标从 0 开始）即最中间的数一定是众数。

方法2：抵消法

循环遍历数组，下一个数相同时计数加1，下一个数不同计数就减去1，当为count==0时，把num[i]赋值给众数，直到最后，得到的数就是众数

import java.util.Arrays;public class FindRepeatNum {public static void main(String[] args) {
//		int[] nums = { 1, 1, 1, 1, 2, 3, 3 };int[] nums = { 2, 2, 1, 1, 1, 2, 2 };
//		int[] nums = { 1, 3, 1, 1, 4, 1, 1, 5, 1, 1, 6, 2, 2 };int result = findRepeatMax(nums);System.out.println("出现次数大于" + nums.length / 2 + "的元素为" + result);int result1 = majorElements(nums);System.out.println("出现次数大于" + nums.length / 2 + "的元素为" + result1);}/** 给定一个大小为 n 的数组 nums，返回其中的多数元素。* 多数元素是指在数组中出现次数大于 n/2 的元素。*/private static int findRepeatMax(int[] nums) {Arrays.sort(nums);return nums[nums.length / 2];}// nums[i] 	1 2 2 1 1 1 1 2 3// major 	1 / 2 / 1 1 1 1 1// count 	1 0 1 0 1 2 3 2 1// nums[i] 	1 2 2 1 1 1 1 2 3// major 	1 2 2 2 1 1 1 1 1// 			  0     0// count. 	1 1 2 1 1 2 3 2 1private static int majorElements(int[] nums) {int majority = nums[0];int count = 1;for (int i = 1; i < nums.length; i++) {if (count == 0) {count++;majority = nums[i];} else if (nums[i] == majority) {count++;} else if (nums[i] != majority) {count--;}
//			if (count == 0) {
//				count++;
//				majority = nums[i];
//			}}return majority;}
}

结果：

2. 综合案例（用户博客管理系统）

Bolg类（抽象类）：

package com.openlab.day13.exer1;public abstract class Blog {final static int Board = 1; // 板块final static int Article = 2; // 文章final static int Author = 3; // 作者final static int Comment = 4; // 作者// 抽象方法：showPage()页面展示public abstract void showPage();
}

Board类：

package com.openlab.day13.exer1;//import java.util.Arrays;public class Board extends Blog {private int id; // 板块idprivate String name; // 板块名称private String intro; // 简介或描述//	开发中尽量使用单项关联，双向关联会造成冗余
//	private Article[] articles;@Overridepublic String toString() {return name;}public Board() {super();}public Board(int id, String name, String intro) {super();this.id = id;this.name = name;this.intro = intro;}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getIntro() {return intro;}public void setIntro(String intro) {this.intro = intro;}@Overridepublic void showPage() {// TODO Auto-generated method stubSystem.out.println("********************模块详情********************");System.out.println("  作者编号：");System.out.println("\t" + this.getId());System.out.println("  作者姓名");System.out.println("\t" + this.getName());System.out.println("  作者简介：");System.out.println("\t" + this.getIntro());System.out.println("************************************************");System.out.println();}}

Author类：

package com.openlab.day13.exer1;//import java.util.Arrays;public class Author extends Blog {private int id; // 作者idprivate String name; // 姓名private String gender; // 性别private int age; // 年龄private String intro = "作者很懒，什么业没留下~"; // 简介或描述
//	private Article[] articles;@Overridepublic String toString() {return name;}public Author(int id, String name, String gender, int age, String intro) {super();this.id = id;this.name = name;this.gender = gender;this.age = age;this.intro = intro;}public Author() {super();}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getGender() {return gender;}public void setGender(String gender) {this.gender = gender;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String getIntro() {return intro;}public void setIntro(String intro) {this.intro = intro;}@Overridepublic void showPage() {// 作者详情页System.out.println("********************作者详情********************");System.out.println("  作者编号：");System.out.println("\t" + this.getId());System.out.println("  作者姓名");System.out.println("\t" + this.getName());System.out.println("  作者性别：");System.out.println("\t" + this.getGender());System.out.println("  作者年龄：");System.out.println("\t" + this.getAge());System.out.println("  作者简介：");System.out.println("\t" + this.getIntro());System.out.println("************************************************");System.out.println();}
}

Article类：

package com.openlab.day13.exer1;import java.util.Date;//import java.util.Arrays;public class Article extends Blog {private int id; // 文章idprivate String tittle; // 标题private String content; // 内容private Author Author; // 作者private Board board; // 所属板块private Date publishTime; // 发布时间private Date modifyTime; // 修改时间@Overridepublic String toString() {return tittle;}public Article(int id, String tittle, String content, Author Author, Board board, Date publishTime,Date modifyTime) {super();this.id = id;this.tittle = tittle;this.content = content;this.Author = Author;this.board = board;this.publishTime = publishTime;this.modifyTime = modifyTime;}public Article() {super();}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getTittle() {return tittle;}public void setTittle(String tittle) {this.tittle = tittle;}public String getContent() {return content;}public void setContent(String content) {this.content = content;}public Author getAuthor() {return Author;}public void setAuthor(Author Author) {this.Author = Author;}public Board getBoard() {return board;}public void setBoard(Board board) {this.board = board;}public Date getPublishTime() {return publishTime;}public void setPublishTime(Date publishTime) {this.publishTime = publishTime;}public Date getModifyTime() {return modifyTime;}public void setModifyTime(Date modifyTime) {this.modifyTime = modifyTime;}@Overridepublic void showPage() {// 文章详情页System.out.println("********************文章详情********************");System.out.println("  文章编号：");System.out.println("\t" + this.getId());System.out.println("  文章标题：");System.out.println("\t" + this.getTittle());System.out.println("  文章作者：");System.out.println("\t" + this.getAuthor());System.out.println("  发布时间：");System.out.println("\t" + this.getPublishTime());System.out.println("  修改时间：");System.out.println("\t" + this.getModifyTime());System.out.println("  文章内容：");System.out.println("\t" + this.getContent());System.out.println("  所属板块：");System.out.println("\t" + this.getBoard());System.out.println("************************************************");System.out.println();}
}

Comment类：

package com.openlab.day13.exer1;import java.util.Date;public class Comment extends Blog {private int id; // 回复idprivate String content; // 内容private Author Author; // 作者private Date publishTime; // 发布时间private Date modifyTime; // 修改时间private Article article; // 文章@Overridepublic String toString() {return content;}public Comment(int id, String content, Author Author, Date publishTime, Date modifyTime, Article article) {super();this.id = id;this.content = content;this.Author = Author;this.publishTime = publishTime;this.modifyTime = modifyTime;this.article = article;}public Comment() {super();}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getContent() {return content;}public void setContent(String content) {this.content = content;}public Author getAuthor() {return Author;}public void setAuthor(Author Author) {this.Author = Author;}public Date getPublishTime() {return publishTime;}public void setPublishTime(Date publishTime) {this.publishTime = publishTime;}public Date getModifyTime() {return modifyTime;}public void setModifyTime(Date modifyTime) {this.modifyTime = modifyTime;}public Article getArticle() {return article;}public void setArticle(Article article) {this.article = article;}@Overridepublic void showPage() {// 文章详情页System.out.println("********************评论详情********************");System.out.println("  评论编号：");System.out.println("\t" + this.getId());System.out.println("  评论作者：");System.out.println("\t" + this.getAuthor());System.out.println("  发布时间：");System.out.println("\t" + this.getPublishTime());System.out.println("  修改时间：");System.out.println("\t" + this.getModifyTime());System.out.println("  评论内容：");System.out.println("\t" + this.getContent());System.out.println("  所属文章：");System.out.println("\t" + this.getArticle());System.out.println("************************************************");System.out.println();}
}

Test类：

package com.openlab.day13.exer1;import java.util.Date;
import java.util.Scanner;public class Test {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);Article article = new Article();Author author = new Author();Board board = new Board();Comment comment = new Comment();author.setId(100001);author.setName("zhang");author.setAge(20);author.setGender("男");author.setIntro("入门程序猿，请多指教！");board.setId(1);board.setName("Java");board.setIntro("Java面向对象编程，文章汇聚地");article.setId(1001);article.setTittle("面向对象三大特征");article.setAuthor(author);article.setPublishTime(new Date());article.setModifyTime(new Date());article.setContent("面向对象的三大特征主要为：封装、继承、多态\n" + "\t    1. 封装\n" + "\t    2. 继承\n" + "\t    3. 多态\n");article.setBoard(board);
//		article.showPage();comment.setId(1);comment.setAuthor(author);comment.setPublishTime(new Date());comment.setModifyTime(new Date());comment.setContent("作者，可以详细说一下什么是封装吗\n");comment.setArticle(article);while (true) {Blog page = null;System.out.println("		用户博客管理系统");System.out.println("************************************************");System.out.println();System.out.println("\t\t1. 模块详情");System.out.println();System.out.println("\t\t2. 文章详情");System.out.println();System.out.println("\t\t3. 作者详情");System.out.println();System.out.println("\t\t4. 评论详情");System.out.println();System.out.println("\t\t5. 退出");System.out.println();System.out.println("************************************************");System.out.print("请输入你的选项(1-5)：");switch (scanner.nextInt()) {case Blog.Board:page = board;break;case Blog.Article:page = article;break;case Blog.Author:page = author;break;case Blog.Comment:page = comment;break;default:System.exit(1);break;}System.out.println();page.showPage();}}
}

结果：

3. （抽象类）定义一个抽象的"Role"类 有姓名 年龄 性别等成员变量

1. 要求尽可能隐藏所有变量(能够私有就私有,能够保护就不要公有) 
    再通过GetXXX()和SetXXX()方法对各变量进行读写。具有一个抽象的play()方法 
    该方法不返回任何值 同时至少定义两个构造方法。Role类中要体现出this的几种用法。
2. 从Role类派生出一个"Employee"类 该类具有Role类的所有成员 
    构造方法除外 并扩展 salary成员变量 同时增加一个静态成员变量“职工编号 ID ”。
    同样要有至少两个构造方法 要体现出this和super的几种用法 
    还要求覆盖play()方法 并提供一个final sing()方法。 
3. "Manager"类继承"Employee"类 有一个final成员变量"vehicle" 
4. 在main()方法中制造Manager和Employee对象,并测试这些对象的方法

Role类：

package com.openlab.day13.exer2;public abstract class Role {private String name;private int age;private String gender;@Overridepublic String toString() {return "姓名：" + name + "，年龄：" + age + "，性别：" + gender + "]";}public Role() {super();}public Role(String name, int age, String gender) {super();this.name = name;this.age = age;this.gender = gender;}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 String getGender() {return gender;}public void setGender(String gender) {this.gender = gender;}public abstract void play();
}

Employee类：

package com.openlab.day13.exer2;public class Employee extends Role {private double salary;private static int id = 1001;@Overridepublic String toString() {return "姓名：" + super.getName() + "，工号：" + Employee.id + "，年龄：" + super.getAge() + "，性别：" + super.getGender() + "，薪水：" + this.salary;}public Employee() {super();}public Employee(String name, int id, int age, String gender, double salary) {super(name, age, gender); // 调用父类的构造方法，一定要放在方法的首个语句this.salary = salary;Employee.id = id;}public double getSalary() {return salary;}public void setSalary(double salary) {this.salary = salary;}public static int getId() {return id;}public static void setId(int id) {Employee.id = id;}@Overridepublic void play() {System.out.println(super.getAge() + "，这个年纪就应该玩！");
;}public final void sing() {System.out.println(this.getName() + "，放声歌唱吧");}
}

Manager类：

package com.openlab.day13.exer2;public class Manager extends Employee {private final String vehicle = "公交";@Overridepublic String toString() {return "姓名：" + super.getName() + "，工号：" + super.getId() + "，年龄：" + super.getAge() + "，性别：" + super.getGender() + "，薪水：" + super.getSalary() + "，交通工具：" + this.vehicle;}public String getVehicle() {return vehicle;}
}

Test类：

package com.openlab.day13.exer2;public class Test {public static void main(String[] args) {Manager manager = new Manager();manager.setAge(20);manager.play();manager.setName("zhang");manager.sing();manager.setGender("男");manager.setSalary(10000);System.out.println(manager);System.out.println(manager.getVehicle());Employee employee1 = new Employee();employee1.setName("wang");employee1.setAge(30);employee1.setGender("男");employee1.setSalary(4000);System.out.println(employee1);employee1.play();employee1.sing();Employee employee = new Employee("li", 1008, 25, "男", 5000);System.out.println(employee);employee.play();employee.sing();Role r1 = new Manager();r1.setAge(18);r1.play();
//		r1.sing();System.out.println(r1);}
}

结果：

4. （抽象类）品尝饮料

1、建立一个Java抽象类Drink，应当

• a、声明一个抽象方法taste() 该方法负责输出饮料的味道
• b、声明int型常量来代表不同的饮料类型 咖啡、啤酒、牛奶
• c、声明静态工厂方法getDrink(int drinkType) 根据传入的参数创建不同的饮料对象 并返回该对象 建议使用switch语句。该方法要求声明DrinkNotFoundException 当没有相对应的饮料类型时 抛出该异常。

2、建立Drink的具体子类

• a、分别建立Drink的子类 Coffee 代表咖啡 Beer 代表啤酒 Milk 代表牛奶 ;
• b、实现taste()方法 要求在控制台打印各自的味道特征。

3、建立异常类DrinkNotFoundException

• a、继承Exception
• b、在Drink的 方 法getDrink(int drinkType)中 声 明 引 发DrinkNotFoundException异常 当传入的参数没有相对应的饮料类型时 抛出异常。
• c、在使用getDrink方法的类中捕捉该异常。

4、建立Test测试类 测试以上内容的正确性

• a、编写main方法 通过命令行传参的方式传入某种饮料的类型。
• b、在main方法中 调用Drink类的getDrink方法 获得相应的饮料对象。注意捕获DrinkNotFoundException。
• c、然后调用该饮料对象的taste()方法 输出该饮料的味道。

5、编译程序 并运行。

注意事项：1、仔细审题 把题目要求理解准确 2、请注意多态性的运用 3、请注意代码的书写、命名符合规范 应有适当的注释

Drink类：

package com.openlab.day13.exer3;public abstract class Drink {// 声明int型常量来代表不同的饮料类型 咖啡、啤酒、牛奶final static int COOFFEE = 1; // 咖啡final static int BEER = 2; // 啤酒final static int MILK = 3; // 牛奶// 声明静态工厂方法getDrink(int drinkType) // 根据传入的参数创建不同的饮料对象,并返回该对象public static Drink getDrink(int drinkType) throws DrinkNotFoundException {switch (drinkType) {case COOFFEE:Coffee coffee = new Coffee();return coffee;case BEER:Beer beer = new Beer();return beer;case MILK:Milk milk = new Milk();return milk;default:throw new DrinkNotFoundException("找不的对应类型的饮料！");}}// 声明一个抽象方法taste(),该方法负责输出饮料的味道public abstract void taste();
}

Coffee类：

package com.openlab.day13.exer3;public class Coffee  extends Drink {// 实现taste()方法@Overridepublic void taste() {System.out.println("咖啡是厚重的苦味");}}

Beer类：

package com.openlab.day13.exer3;public class Beer extends Drink {// 实现taste()方法@Overridepublic void taste() {// 打印各自的味道特征。System.out.println("啤酒是略微的苦涩味道");}}

MilK类：

package com.openlab.day13.exer3;public class Milk extends Drink {// 实现taste()方法@Overridepublic void taste() {System.out.println("牛奶奶香味特别浓的");}}

DrinkNotFoundException异常类：

package com.openlab.day13.exer3;// 建立异常类DrinkNotFoundException，继承Exception 
public class DrinkNotFoundException extends Exception {static final long serialVersionUID = -3387516993124229948L;public DrinkNotFoundException(String message) {super(message);}
}

Test类：

package com.openlab.day13.exer3;import java.util.Scanner;public class Test {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);int i = 0;while (i < 4) {System.out.println("请输入你要和的饮料的类型(1.coffee,2.beer,3.milk)：");int type = scanner.nextInt(); // 控制台输入饮料类型Drink drink1 = null;try {drink1 = Drink.getDrink(type);} catch (DrinkNotFoundException e) {// 异常捕获System.out.println("Exception thrown  :" + e);continue;
//				e.printStackTrace();}drink1.taste();  // 调用该饮料对象的tastei++;}scanner.close();}
}

结果：

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