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 1
	private 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id
	private 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;

	@Override
	public 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;
	}

	@Override
	public void showPage() {
		// TODO Auto-generated method stub
		System.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id
	private 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;

	@Override
	public 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;
	}

	@Override
	public 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id
	private 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
	@Override
	public 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;
	}

	@Override
	public 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id
	private 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

	@Override
	public 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;
	}

	@Override
	public 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;

	@Override
	public 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;

	@Override
	public 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;
	}

	@Override
	public 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";
	
	@Override
	public 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
	@Override
	public 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
	@Override
	public 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
	@Override
	public 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taste
			i++;
		}
		scanner.close();
	}
}

结果：