Object-oriented, constructors (constructors) are used to initialize properties when creating objects, and this is used to refer to the current class.

public class Test01 {
	public static void main(String[] args) {
		Circle c1 = new Circle(1.2);
		c1.showArea();
		c1.showPerimeter();
	}
}
class Circle {
	private double radius;

	public Circle(double radius) {
		this.radius = radius;
	}

	public Circle() {
	}

	public double getRadius() {
		return radius;
	}

	public void setRadius(double radius) {
		this.radius = radius;
	}
	
	public void showArea(){
		System.out.println("radius:"+radius + area:"+3.14 * radius * radius);
	}
	
	public void showPerimeter(){
		System.out.println("radius:"+radius + perimeter: "+2 * 3.14 * radius);
	}
}

Question 2

• Define a date MyDate Class.

• Attributes:

  • year: year

  • month: month

  • day: day

• Construction method:

  • Full-parameter Construction Method

• Membership methods:

  • get/set Method

  • void showDate Method: Print date.

  • boolean isLeapYear()Method: To determine whether the current date is a leap year or not.

Code implementation:

public class Test02 {
	public static void main(String[] args) {
		MyDate my = new MyDate(2019,5,13);
		my.showDate();
		boolean flag = my.isLeapYear();
		System.out.println(my.getYear()+ (flag?"It's a leap year.":"Not a leap year"));
	}
}

class MyDate {
	private int year;
	private int month;
	private int day;

	public MyDate() {
	}

	public MyDate(int year, int month, int day) {
		this.year = year;
		this.month = month;
		this.day = day;
	}

	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;
	}

	public void showDate() {
		System.out.println("date" + year + "year" + month + "month" + day + "day");
	}

	public boolean isLeapYear() {
		return year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
	}
}

public class Test03 {
	public static void main(String[] args) {
		Card c = new Card("spades", "A");
		c.showCard();
	}
}

class Card {
	private String hua;
	private String dian;

	public Card(String hua, String dian) {
		this.hua = hua;
		this.dian = dian;
	}

	public Card() {
	}

	public String getHua() {
		return hua;
	}

	public void setHua(String hua) {
		this.hua = hua;
	}

	public String getDian() {
		return dian;
	}

	public void setDian(String dian) {
		this.dian = dian;
	}

	public void showCard() {
		System.out.println(hua + dian);
	}
}

Question 4

• Create a Book Class, property privatization, providing parametric and nonparametric constructs, get/set
• Establish TestBook Class, and create Book Array, create multiple Book Objects, stored in arrays, and traversed to display their information, sorted by volume from high to low

Code implementation:

	public static void main(String[] args) {
		Book[] all = new Book[5];
		
		all[0] = new Book(1, "<From Introduction to Proficiency", "Zhang San", 88, 100, 1000);
		all[1] = new Book(2, "<From Initial to Abandoned", "Li Si", 89, 200, 800);
		all[2] = new Book(3, "<From Introduction to Hair Loss", "Wang Wu", 56, 10, 500);
		all[3] = new Book(4, "<From Initial to Drug-taking ____________", "Zhao Liu", 100, 180, 900);
		all[4] = new Book(5, "<From Introduction to Immortality", "Money seven", 99, 0, 1000);

		System.out.println("Before sorting:");
		System.out.println("number\t Title\t\t author\t Price\t Sales volume\t Stock");
		for (int i = 0; i < all.length; i++) {
			System.out.println(all[i].getInfo());
		}
		
		//sort
		for (int i = 1; i < all.length; i++) {
			for (int j = 0; j < all.length-i; j++) {
				if(all[j].getSales() < all[j+1].getSales()){
					Book temp = all[j];
					all[j] = all[j+1];
					all[j+1] = temp;
				}
			}
		}
		System.out.println("After sorting:");
		System.out.println("number\t Title\t\t author\t Price\t Sales volume\t Stock");
		for (int i = 0; i < all.length; i++) {
			System.out.println(all[i].getInfo());
		}
	}
}

class Book {
	private Integer id;
	private String title;
	private String author;
	private double price;
	private Integer sales;
	private Integer stock;
	public Book() {
	}
	public Book(Integer id, String title, String author, double price, Integer sales, Integer stock) {
		this.id = id;
		this.title = title;
		this.author = author;
		this.price = price;
		this.sales = sales;
		this.stock = stock;
	}
	
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getTitle() {
		return title;
	}
	public void setTitle(String title) {
		this.title = title;
	}
	public String getAuthor() {
		return author;
	}
	public void setAuthor(String author) {
		this.author = author;
	}
	public double getPrice() {
		return price;
	}
	public void setPrice(double price) {
		this.price = price;
	}
	public Integer getSales() {
		return sales;
	}
	public void setSales(Integer sales) {
		this.sales = sales;
	}
	public Integer getStock() {
		return stock;
	}
	public void setStock(Integer stock) {
		this.stock = stock;
	}
	
	public String getInfo(){
		return id + "\t" + title + "\t" + author + "\t" + price + "\t" + sales + "\t" + stock;
	}
}

public class Employee {
	private int id;
	private String name;
	private int age;
	private String tel;
	
	public Employee() {
		super();
	}

	public Employee(int id, String name, int age, String tel) {
		super();
		this.id = id;
		this.name = name;
		this.age = age;
		this.tel = tel;
	}

	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 int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public String getTel() {
		return tel;
	}

	public void setTel(String tel) {
		this.tel = tel;
	}
	
	public String getInfo(){
		return "Number:" + name + ", name:" + name + ", age:" + age + ", telephone:" + tel;
	}
}

public class Programmer extends Employee{
	private String language;

	public Programmer() {
		super();
	}

	public Programmer(int id, String name, int age, String tel, String language) {
		super(id, name, age, tel);
		this.language = language;
	}

	public String getLanguage() {
		return language;
	}

	public void setLanguage(String language) {
		this.language = language;
	}

	@Override
	public String getInfo() {
		return super.getInfo() + "，Programing language:" + language;
	}
	
}

public class Designer extends Programmer {
	private double bonus;

	public Designer() {
		super();
	}

	public Designer(int id, String name, int age, String tel, String language, double bonus) {
		super(id, name, age, tel, language);
		this.bonus = bonus;
	}

	public double getBonus() {
		return bonus;
	}

	public void setBonus(double bonus) {
		this.bonus = bonus;
	}

	@Override
	public String getInfo() {
		return super.getInfo() + "，Bonus:" + bonus;
	}
	
}

public class Architect extends Designer {
	private int stock;

	public Architect() {
		super();
	}

	public Architect(int id, String name, int age, String tel, String language, double bonus, int stock) {
		super(id, name, age, tel, language, bonus);
		this.stock = stock;
	}


	public int getStock() {
		return stock;
	}

	public void setStock(int stock) {
		this.stock = stock;
	}

	@Override
	public String getInfo() {
		return super.getInfo() + "，Number of shares held:" + stock;
	}
	
}

public class Test05 {
	public static void main(String[] args) {
		Employee emp = new Employee(1, "Zhang San", 23, "10086");
		Programmer pro = new Programmer(2, "Li Si", 24, "10010", "java");
		Designer de = new Designer(3, "Wang Wu", 25, "114", "python", 2000);
		Architect a = new Architect(4, "Zhao Liu", 26, "110", "java", 3000, 100);
		
		System.out.println(emp.getInfo());
		System.out.println(pro.getInfo());
		System.out.println(de.getInfo());
		System.out.println(a.getInfo());
	}
}

Anything you don't know can be left below, I will answer them one by one.