第四章：封装、继承与多态

课件

面向对象的三大特性：封装

Circle1类

package cn.edu.bjut.chapter4;
 
public class Circle1 {
	private double radius; 
 
	public Circle1(double radius) {
		this.radius = radius; 
	}
 
	public double getRadius() {
		return radius;
	}
 
	public void setRadius(double radius) {
		this.radius = radius;
	}
 
	public double area() {
		return (Math.PI * radius * radius); 
	}
 
	public double perimeter() {
		return (2 * Math.PI * radius); 
	}
}

Circle2类

Circle2.java

package cn.edu.bjut.chapter4;
 
public class Circle2 {
	private double diameter; 
 
	public Circle2(double radius) {
		this.diameter = 2 * radius; 
	}
 
	public double getRadius() {
		return (diameter / 2);
	}
 
	public void setRadius(double radius) {
		this.diameter = radius * 2;
	}
 
	public double area() {
		return (Math.PI * diameter * diameter / 4); 
	}
 
	public double perimeter() {
		return (Math.PI * diameter); 
	}
}

测试类：CircleTester类

CircleTester.java

package cn.edu.bjut.chapter4;
 
public class CircleTester {
	public static void main(String[] args) {
		Circle1 c1 = new Circle1(5); 
		Circle2 c2 = new Circle2(5); 
 
		System.out.println(c1.area() + "\t" + c2.area());
		System.out.println(c1.perimeter() + "\t" + c2.perimeter());
	}
}

继承：访问控制符

父类：Card类

Card.java

package cn.edu.bjut.chapter4;
 
public abstract class Card {
	protected String accountNumber; // 账号
	protected double balance; // 余额
 
	public Card(String accountNumber, double balance) {
		this.accountNumber = accountNumber;
		this.balance = (balance >= 0 ? balance : 0); 
	}
 
	public String getAccountNumber() {
		return this.accountNumber;
	}
 
	public void setAccountNumber(String accountNumber) {
		this.accountNumber = accountNumber;
	}
 
	public double getBalance() {
		return this.balance;
	}
 
	public boolean deposit(double money) {
		if (money <= 0) {
			return false; 
		}
 
		this.balance += money;
		return true;
	}
 
	public abstract boolean draw(double money); 
}

子类：CreditCard类

CreditCard.java

package cn.edu.bjut.chapter4;
 
public class CreditCard extends Card {
	private double overdraftLimit; // 透支额度
 
	public CreditCard(String accountNumber, double balance, 
			double overdraftLimit) {
		super(accountNumber, balance);
		this.overdraftLimit = overdraftLimit;
	}
 
	public CreditCard(String accountNumber, double overage) {
		this(accountNumber, overage, 0);
	}
 
	public double getOverdraftLimit() {
		return this.overdraftLimit;
	}
 
	public void setOverdraftLimit(double overdraftLimit) {
		this.overdraftLimit = (overdraftLimit >= 0 ? overdraftLimit : 0);
	}
 
	@Override
	public boolean draw(double money) {
		if (balance + overdraftLimit < money) {
			return false;
		}
 
		balance -= money;
		return true;
	}
}

子类：DebitCard类

DebitCard.java

package cn.edu.bjut.chapter4;
 
public class DebitCard extends Card {
	public DebitCard(String accountNumber, double balance) {
		super(accountNumber, balance);
	}
 
	@Override
	public boolean draw(double money) {
		if (balance < money) {
			return false;
		}
 
		balance -= money;
		return true;
	}
}

测试类：CardTester类

CardTester.java

package cn.edu.bjut.chapter4;
 
public class CardTester {
	public static void main(String[] args) {
		System.out.println("------------  借记卡账户  ------------");
		Card debitCard = new DebitCard("CHK20100117001", 100);
		System.out.println("取90元的结果：" + debitCard.draw(90));
		debitCard.deposit(90);
		System.out.println("取120元的结果：" + debitCard.draw(120));
 
		System.out.println("------------  信用卡账户  ------------");
		Card crebitCard = new CreditCard("CHK20100117002", 100, 50);
		System.out.println("取90元的结果：" + crebitCard.draw(90));
		crebitCard.deposit(90);
		System.out.println("取120元的结果：" + crebitCard.draw(120));
		crebitCard.deposit(120);
		System.out.println("取160元的结果：" + crebitCard.draw(160));
	}
}

继承中的成员方法覆盖

父类：Rectangle类

Rectangle.java

package cn.edu.bjut.chapter4;
 
public class Rectangle {
	protected int length, width;
 
	public Rectangle(int length, int width) {
		this.length = length;
		this.width = width;
	}
	public int area() {
		System.out.println(this.getClass().getName());
		return (length * width);
	}
	public int perimeter() {
		System.out.println(this.getClass().getName());
		return (2 * (length + width));
	}
}

子类：Square类

Square.java

package cn.edu.bjut.chapter4;
 
public class Square extends Rectangle {
	public Square(int length) {
		super(length, length); 
	}
 
	public int area() {
		System.out.println(this.getClass().getName());
		return (length * length); 
	}
 
	public int perimeter() {
		System.out.println(this.getClass().getName());
		return (length << 2); 
	}
}

测试类：SquareTester类

SquareTester.java

package cn.edu.bjut.chapter4;
 
public class SquareTester {
	public static void main(String[] args) {
		Rectangle rect = new Square(6); 
 
		System.out.println(rect.area());
		System.out.println(rect.perimeter());
	}
}

继承中的数据成员隐藏

PropertyHiddenTester.java

package cn.edu.bjut.chapter4;
 
class ClassA {
	int a = 20; 
}
 
class ClassB extends ClassA {
	int a = 30; 
	public void print() {
		System.out.println(a + "\t" + super.a);
	}
}
 
public class PropertyHiddenTester {
	public static void main(String[] args) {
		ClassB classB = new ClassB(); 
		classB.print();
	}
}

父类引用强转为子类引用

父类：Person类

Person.java

package cn.edu.bjut.chapter4;
 
public class Person {
	protected String id; //身份证号
	protected String name; // 姓名
	protected char gender; // 性别
 
	public Person(String id, String name, char gender) {
		this.id = id; 
		this.name = name; 
		this.gender = gender; 
	}
 
	public String getId() {
		return id;
	}
 
	public void setId(String id) {
		this.id = id;
	}
 
	public String getName() {
		return name;
	}
 
	public void setName(String name) {
		this.name = name;
	}
 
	public char getGender() {
		return gender;
	}
 
	public void setGender(char gender) {
		this.gender = gender;
	}
}

子类：Student类

Student.java

package cn.edu.bjut.chapter4;
 
public class Student extends Person {
	private String studentId; // 学号
	private String classNo;  //班级
 
	public Student(String id, String name, char gender, 
			String studentId, String classNo) {
		super(id, name, gender);
 
		this.studentId = studentId; 
		this.classNo = classNo; 
	}
 
	public String getStudentId() {
		return studentId;
	}
 
	public void setStudentId(String studentId) {
		this.studentId = studentId;
	}
 
	public String getClassNo() {
		return classNo;
	}
 
	public void setClassNo(String classNo) {
		this.classNo = classNo;
	}
}

子类：Teacher类

Teacher.java

package cn.edu.bjut.chapter4;
 
public class Teacher extends Person {
	private String teacherId; // 职工号
	private String title; //职称
 
	public Teacher(String id, String name, char gender, 
			String teacherId, String title) {
		super(id, name, gender); 
		this.teacherId = teacherId; 
		this.title = title; 
	}
	public String getTeacherId() {
		return teacherId;
	}
	public void setTeacherId(String teacherId) {
		this.teacherId = teacherId;
	}
	public String getTitle() {
		return title;
	}
	public void setTitle(String title) {
		this.title = title;
	}
}

测试类：PersonTester类

PersonTester.java

package cn.edu.bjut.chapter4;
 
public class PersonTester {
	public static void main(String[] args) {
		Person p1 = new Student("123456789", "李文慧", '女', "052615", "05"); 
		Person p2 = new Teacher("987654321", "梁化祥", '男', "071235", "教授"); 
 
		System.out.println(p1.getId() + "\t" + p1.getName() + "\t" + p1.getGender());
		//System.out.println(p1.getStudentId() + "\t" + p1.getClassNo());
		System.out.println(p2.getId() + "\t" + p2.getName() + "\t" + p2.getGender());
		//System.out.println(p2.getTeacherId() + "\t" + p2.getTitle());
 
		if (p1 instanceof Student) {
			Student stu = (Student) p1; 
			System.out.println(stu.getStudentId() + "\t" + stu.getClassNo());
		}
 
		if (p2 instanceof Teacher) {
			Teacher tea = (Teacher) p2; 
			System.out.println(tea.getTeacherId() + "\t" + tea.getTitle());
		}
	}
}

抽象类与抽象方法

抽象父类：Shape类

Shape.java

package cn.edu.bjut.chapter4_1;
 
public abstract class Shape {
	public abstract double area(); 
	public abstract double perimeter(); 
}

子类：Rectangle类

Rectangle.java

package cn.edu.bjut.chapter4_1;
 
public class Rectangle extends Shape {
	private double length, width; 
 
	public Rectangle(double length, double width) {
		this.length = length; 
		this.width = width; 
	}
 
	@Override
	public double area() {
		return (length * width);
	}
 
	@Override
	public double perimeter() {
		return (2 * (length + width));
	}
 
}

子类：Circle类

Circle.java

package cn.edu.bjut.chapter4_1;
 
public class Circle extends Shape {
	private double radius; 
 
	public Circle(double radius) {
		this.radius = radius; 
	}
 
	@Override
	public double area() {
		return (Math.PI * radius * radius);
	}
 
	@Override
	public double perimeter() {
		return (2 * Math.PI * radius);
	}
}

子类：Triangle类

Triangle.java

package cn.edu.bjut.chapter4_1;
 
public class Triangle extends Shape {
	private double a, b, c; 
 
	public Triangle(double a, double b, double c) {
		this.a = a; 
		this.b = b; 
		this.c = c; 
	}
 
	@Override
	public double area() {
		double p = (a + b + c) / 2; 
 
		return Math.sqrt(p * (p - a) * (p - b) * (p - c)); 
	}
 
	@Override
	public double perimeter() {
		return (a + b + c);
	}
}

接口

抽象父类：Animal

Animal.java

package cn.edu.bjut.chapter4;
 
public abstract class Animal {
	protected String name; 
 
	public Animal(String name) {
		this.name = name; 
	}
 
	public String getName() {
		return name;
	}
 
	public void setName(String name) {
		this.name = name;
	}
 
	public abstract String makeNoise(); 
}

接口：Runable

Runable.java

package cn.edu.bjut.chapter4;
 
public interface Runable {
	String UNIT = "千米/小时"; 
 
	double getSpeed(); 
}

接口：Flyable

Flyable.java

package cn.edu.bjut.chapter4;
 
public interface Flyable {
	String UNIT = "千米"; 
 
	double getFlightHeight(); 
}

子类：Dog

Dog.java

package cn.edu.bjut.chapter4;
 
public class Dog extends Animal implements Runable {
	private double speed; 
 
	public Dog(String name, double speed) {
		super(name);
		this.speed = speed; 
	}
 
	@Override
	public String makeNoise() {
		return "汪！汪！汪！";
	}
 
	@Override
	public double getSpeed() {
		return speed;
	}
 
	@Override
	public String toString() {
		return "Dog [奔跑速度：" + speed + Runable.UNIT + "]";
	}
}

子类：Pigeon

Pigeon.java

package cn.edu.bjut.chapter4;
 
public class Pigeon extends Animal implements Flyable, Runable {
	private double flightHeight; 
	private double speed; 
 
	public Pigeon(String name, double flightHeight, double speed) {
		super(name);
		this.flightHeight = flightHeight; 
		this.speed = speed; 
	}
 
	@Override
	public double getFlightHeight() {
		return flightHeight;
	}
	@Override
	public String makeNoise() {
		return "咕！咕！咕！";
	}
	@Override
	public double getSpeed() {
		return speed; 
	}
	@Override
	public String toString() {
		return "Pigeon [飞行高度：" + flightHeight + Flyable.UNIT 
				+ ", 奔跑速度：" + speed + Runable.UNIT + "]";
	}
}

测试类：AnimalTester.java

AnimalTester.java

package cn.edu.bjut.chapter4;
 
public class AnimalTester {
	public static void main(String[] args) {
		Dog dog = new Dog("小毛绒", 20); 
		Pigeon pigeon = new Pigeon("捣蛋鬼", 0.5, 5); 
 
		System.out.println(dog);
		System.out.println(pigeon); 
	}
}

Java8新特性：default与static

InterfaceNewFeatureTester.java

package cn.edu.bjut.chapter4;
 
interface Drawable {
	void draw(); 
 
	default void msg() {
		System.out.println("default method");
	}
 
	static int cube (int x) {
		return (x * x * x); 
	}
}
 
class Circle implements Drawable {
	@Override
	public void draw() {
		System.out.println("drawing circle");
	}
}
 
public class InterfaceNewFeatureTester {
	public static void main(String[] args) {
		Drawable d = new Circle(); 
		d.draw();
		d.msg(); 
		System.out.println(Drawable.cube(3));
	}
}

上机作业

专利文档中不仅有IPC分类号，还有CPC分类号，CPC的格式与IPC类似，但多了两个字段position和value，这两个字段取值为单个字符，请重写Ipc类和Cpc类，并增加一个父类Classification；

【参考答案】

Classification.java

package cn.edu.bjut.chapter4;
 
public class Classification {
	protected char section;
	protected int mainClass;
	protected char subclass;
	protected int mainGroup;
	protected int subgroup;
 
	public final static char SEPARATOR = '/';
 
	public Classification(char section, int mainClass, char subclass, int mainGroup, int subgroup) {
		this.section = section;
		this.mainClass = mainClass;
		this.subclass = subclass;
		this.mainGroup = mainGroup;
		this.subgroup = subgroup;
	}
 
	// example: G09F 17/30
	public Classification(String symbol) {
		this.section = symbol.charAt(0);
		this.mainClass = Integer.parseInt(symbol.substring(1, 3));
		this.subclass = symbol.charAt(3);
 
		int pos = symbol.indexOf(SEPARATOR);
		this.mainGroup = Integer.parseInt(symbol.substring(4, pos).trim());
		this.subgroup = Integer.parseInt(symbol.substring(pos + 1));
	}
 
	public char getSection() {
		return section;
	}
 
	public void setSection(char section) {
		this.section = section;
	}
 
	public int getMainClass() {
		return mainClass;
	}
 
	public void setMainClass(int mainClass) {
		this.mainClass = mainClass;
	}
 
	public char getSubclass() {
		return subclass;
	}
 
	public void setSubclass(char subclass) {
		this.subclass = subclass;
	}
 
	public int getMainGroup() {
		return mainGroup;
	}
 
	public void setMainGroup(int mainGroup) {
		this.mainGroup = mainGroup;
	}
 
	public int getSubgroup() {
		return subgroup;
	}
 
	public void setSubgroup(int subgroup) {
		this.subgroup = subgroup;
	}
 
	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder();
 
		sb.append(section);
 
		String strMainClass = String.format("%2s", mainClass).replace(' ', '0');
		sb.append(strMainClass);
 
		sb.append(subclass);
 
		String strMainGroup = String.format("%4s", mainGroup);
		sb.append(strMainGroup);
 
		sb.append(SEPARATOR);
 
		sb.append(subgroup);
 
		return sb.toString();
	}
}

Ipc.java

package cn.edu.bjut.chapter4;
 
public class Ipc extends Classification {
 
	public Ipc(char section, int mainClass, char subclass, int mainGroup, int subgroup) {
		super(section, mainClass, subclass, mainGroup, subgroup); 
	}
 
	public Ipc(String symbol) {
		super(symbol); 
	}
 
	public static void main(String[] args) {
		char section = 'A'; 
		int mainClass = 4; 
		char subclass = 'B'; 
		int mainGroup = 55; 
		int subgroup = 56; 
 
		Classification ipc = new Ipc(section, mainClass, subclass, mainGroup, subgroup); 
		System.out.println(ipc); 
 
		String symbol = "G09F 17/30"; 
		System.out.println(new Ipc(symbol)); 
	}
}

Cpc.java

package cn.edu.bjut.chapter4;
 
public class Cpc extends Classification {
	private char position; 
	private char value; 
 
	public Cpc(char section, int mainClass, char subclass, int mainGroup, int subgroup, char position, char value) {
		super(section, mainClass, subclass, mainGroup, subgroup); 
 
		this.position = position; 
		this.value = value; 
	}
 
	public Cpc(String symbol, char position, char value) {
		super(symbol); 
 
		this.position = position; 
		this.value = value; 
	}
 
	public char getPosition() {
		return position;
	}
 
	public void setPosition(char position) {
		this.position = position;
	}
 
	public char getValue() {
		return value;
	}
 
	public void setValue(char value) {
		this.value = value;
	}
}

仔细观察身边的事物，对其进行抽象化处理，但需包括父类和父接口等。

返回Java课程页

目录

第四章：封装、继承与多态

课件

面向对象的三大特性：封装

Circle1类

Circle2类

测试类：CircleTester类

继承：访问控制符

父类：Card类

子类：CreditCard类

子类：DebitCard类

测试类：CardTester类

继承中的成员方法覆盖

父类：Rectangle类

子类：Square类

测试类：SquareTester类

继承中的数据成员隐藏

父类引用强转为子类引用

父类：Person类

子类：Student类

子类：Teacher类

测试类：PersonTester类

抽象类与抽象方法

抽象父类：Shape类

子类：Rectangle类

子类：Circle类

子类：Triangle类

接口

抽象父类：Animal

接口：Runable

接口：Flyable

子类：Dog

子类：Pigeon

测试类：AnimalTester.java

Java8新特性：default与static

上机作业