Java入门——day47

1.定义一个基类Shape，在此基础上派生出Rectangle和Circle，二者都有getArea()函数计算对象的面积。使用Rectangle类创建一个派生类Square。

//基类Shape
class Shape {
    public double getArea() {
        return 0;
    }
}
//Rectangle类继承Shape类
class Rectangle extends Shape {
    private double len;
    private double width;
    public Rectangle(double len, double width) {
        super();
        this.len = len;
        this.width = width;
    }
    public double getArea() {
        return len * width;
    }
}
//Circle类继承Shape类
class Circle extends Shape {
    private double r;
    public Circle(double r) {
        super();
        this.r = r;
    }
    public double getArea() {
        return 3.14 * r * r;
    }
}
//Square类继承Rectangle类
public class Square extends Rectangle {
    public Square(double len, double width) {
        super(len, width);
    }
    public static void main(String[] args) {
        Shape p = new Rectangle(3, 6);
        System.out.println("The area of the rectangle is " + p.getArea());
        p = new Circle(3);
        System.out.printf("The area of the circle is %.2f\n", p.getArea());
        p = new Square(4, 4);
        System.out.println("The area of the square is " + p.getArea());
    }
}

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2.定义一个哺乳动物类Mammal，再由此派生出狗类Dog，定义一个Dog类的对象，观察基类和派生类的构造函数的调用顺序。

//父类Mammal类
class Mammal{
    private String name;
    private int age;
    public Mammal(String name, int age) {
        this.name=name;
        this.age=age;
        System.out.println("构造哺乳动物类");
    }
    public String getName() {
        return name;
    }
    public int getAge() {
        return age;
    }
}
//Dog类继承Mammal类
public class Dog extends Mammal{
    private int leg; 
    public Dog(String name, int age, int leg) {
        super(name, age);
        this.leg=leg;
        System.out.println("构造狗类");
    }
    public void display() {
        System.out.println("Name："+getName());
        System.out.println("Age："+getAge());
        System.out.println("Leg："+leg);
    }
    public static void main(String[] args) {
        Dog p=new Dog("Sera",5,4);
        p.display();
    }
}

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3.定义一个基类及其派生类，在构造函数中输出提示提示信息，构造派生类的对象，观察构造函数的执行情况。

//父类Base类
class Base{
    public Base() {
        System.out.println("构造基类");
    }
}
//Derived类继承Base类
class Derived extends Base{
    public Derived() {
        System.out.println("构造派生类");
    }
    
}
public class Test {
    public static void main(String[] args) {
        Derived p=new Derived();
    }
}

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 4.定义一个Document类，有数据成员name，从Document派生Book类，增加数据成员pageCount。

//父类Document类
class Document{
    private String name; //书名
    public Document(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }
}
//子类Book类
public class Book extends Document{
    private int pageCount; //页数
    public Book(String name,int pageCount) {
        super(name);
        this.pageCount=pageCount;
    }
    public void display() {
        System.out.println("Name："+getName());
        System.out.println("PageCount："+pageCount);
    }
    public static void main(String[] args) {
        Book b=new Book("Java程序设计",425);
        b.display();
    }
}

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5.定义一个Object1类，有数据成员weight及相应的操作函数，由此派生出Box类，增加数据成员height和width及相应的操作函数，声明一个Box对象，观察构造函数的调用顺序。

//父类Object1类
class Object1{
    private float weight;
    public Object1(float weight) {
        this.weight=weight;
        System.out.println("构造Object1类");
    }
    public float getWeight() {
        return weight;
    }
}
//子类Box类
public class Box extends Object1{
    private float height;
    private float width;
    public Box(float weight,float height,float width) {
        super(weight);
        this.height=height;
        this.width=width;
        System.out.println("构造Box类");
    }
    public void display() {
        System.out.println("The weight of the box is "+getWeight());
        System.out.println("The height of the box is "+height);
        System.out.println("The width of the box is "+width);
    }
    public static void main(String[] args) {
        Box b=new Box(1.2f,1,0.8f);
        b.display();
    }
}

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 6.定义一个基类BaseClass，从它派生出类DerivedClass。BaseClass有成员函数fn1()，fn2()，DerivedClass也有成员函数fn1()，fn2()。在主函数中声明对象来调用fn1()，fn2()，观察运行结果。

//基类BaseClass
class BaseClass{
    public void fn1() {
        System.out.println("Base.fn1");
    }
    public void fn2() {
        System.out.println("Base.fn2");
    }
}
//子类DerivedClass
public class DerivedClass extends BaseClass {
    public void fn1() {
        System.out.println("Derived.fn1");
    }
    public void fn2() {
        System.out.println("Derived.fn2");
    }
    public static void main(String[] args) {
        DerivedClass m=new DerivedClass();
        m.fn1();
        m.fn2();
        BaseClass n=new BaseClass();
        n.fn1();
        n.fn2();
        n=new DerivedClass();
        n.fn1();
        n.fn2();
    }
}