Java入门知识1

1. 获取标准屏幕的输入时，需导入java.util.Scanner包。

2. 主类的名称与.java的文件名需一致。

3. 文件中主类设置为public，其他类前面无需加访问级别。

4. 继承时，使用extends关键字，访问父类的成员时，使用super。

import java.util.Scanner;

class Circle{
    private double radius;
    
    public Circle(){
    radius = 0.0;
    }
    public Circle( double radius0 ){
        radius = radius0;
    }

    public double getRadius(){
        return radius;
    }

    public double getArea(){
        return 3.14*radius*radius;
    }
    
    public double getLength(){
        return 2*3.14*radius;
    }
    
    public void Display(){
        System.out.println( "Radius is: " + radius );
        System.out.println( "Length is: " + getLength() );
        System.out.println( "Area is: " + getArea() );
    }
}

class Cylinder extends Circle{
    private double height;
    
    public Cylinder( double height0, double radius0 ){
        super( radius0 );
        height = height0;
    }
    
    public double getHeight(){
        return height;
    }
    
    public double getRadius(){
        return super.getRadius();
    }
    
    public double getArea(){
        double area0 = super.getLength()*height;
        double area1 = super.getArea()*2;
        return area0 + area1;
    }
    
    public double getVolume(){
        return super.getArea()*height;
    }
    
    public void Display(){
        System.out.println( "Radius is: " + super.getRadius() );
        System.out.println( "Height is: " + height );
        System.out.println( "Area is: " + getArea() );    
        System.out.println( "Volume is: " + getVolume() );
    }

}

public class TestCylinder {
    public static void main(String[] args) {
        Scanner sc = new Scanner( System.in );
        
        System.out.println( "Please input radius:" );
        double radius = sc.nextDouble();
        System.out.println( "Please input height:" );
        double height = sc.nextDouble();
        
        Circle circle = new Circle( radius );
        Cylinder cylinder = new Cylinder( height, radius );
        
        circle.Display();
        cylinder.Display();    
    }
}