继承

package com.atguigu.exer;


public class People{
	String name = new String();
	int age;
	
	public People() {
		
	}
	public People(String name,int age) {
		this();
		this.name = name;
		this.age = age;
	}
	
	public void eat() {
		System.out.println("im eating");
	}
}

package com.atguigu.exer;

public class Student extends People{
	String major;
	
	public Student() {
		
	}

}

package com.atguigu.exer;

public class Text {
	public static void main(String[] args) {
		People p = new People();
		p.age = 99;
		p.name = "扎根";
		
		Student s = new Student();
		s.name = "wse";
		System.out.println(s.name);//wse
		s.eat();//im eating
	}
}

继承的格式：
class A extends B{}
A：子类、派生类、subclass
B：父类、超类、基类

体现：一旦子类A继承父类B，A获取了父类B中声明的结构

子类继承父以后，还能声明自己特有的属性或方法，实现功能的拓展
在这里插入图片描述

一个类只能有一个父类

如果没有显式声明一个父类的化，则此类继承于java.lang.Object类
所有java类除Object都直接或间接继承Object类

例子：
在这里插入图片描述

package com.atguigu.CylinderCul;

public class Circle {
	private double radius;

	public double getRadius() {
		return radius;
	}

	public void setRadius(int radius) {
		this.radius = radius;
	}
	
	public Circle() {
		this.radius = 1;//初始化半径为1
	}
	
	public double findArea() {
		return this.radius*this.radius*Math.PI;
	}
}

package com.atguigu.CylinderCul;

public class Cylinder extends Circle{
	//圆柱
	private double length;

	public double getLength() {
		return length;
	}

	public void setLength(double length) {
		this.length = length;
	}
	
	public double findVolume() {
		return this.findArea() * this.length;
	}
	
}

package com.atguigu.CylinderCul;

public class Test {
	public static void main(String[] args) {
		Cylinder cylinder = new Cylinder();
		cylinder.setRadius(3);
		cylinder.setLength(5);
		double v = cylinder.findVolume();
		System.out.println(v);//141.3716694115407
	}
}