抽象类

类的设计应该保证父类和子类能够共享特征。有时将一个父类设计的非常抽象，以至于它没有

具体的实例，这样的就可以声明为抽象类。

用abstract关键字修饰一个类，这个类就是抽象类

用abstract来修饰一个方法时，这个方法就是抽象方法

抽象方法：只有方法声明，没有方法的实现以分号结束abstract int abstractMethod(int a);

含有抽象方法的类必须被声明为抽象类抽象类是用来被继承的，抽象类的子类必须重写父类的抽象方法，并提供方法体。若没有重写全部的抽象方法，仍为抽象类。

不能用abstract修饰属性、私有方法、构造器、静态方法、final的方法。

抽象类不能被实例化。

public abstract class Pet {
	private String name;
	private int age;
	private double weight;

	
	public Pet(String name, int age, double weight) {
		this.name = name;
		this.age = age;
		this.weight = weight;
	}
	
	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 double getWeight() {
		return weight;
	}
	public void setWeight(double weight) {
		this.weight = weight;
	}

	public String toString() {
		
		return "名字："+name+"，年龄："+age+",重量："+weight;
	}
	public abstract void speak();
	
	public abstract void eat();
}
class PetT{
  public static void main(String[] args) {
	Pet p=	 new Pet("测试",20,50);//抽象类不可以new对象
 }
}

一个继承抽象类父类的子类

public abstract class Pet {
	private String name;
	private int age;
	private double weight;

	
	public Pet(String name, int age, double weight) {
		this.name = name;
		this.age = age;
		this.weight = weight;
	}
	
	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 double getWeight() {
		return weight;
	}
	public void setWeight(double weight) {
		this.weight = weight;
	}

	public String toString() {
		
		return "名字："+name+"，年龄："+age+",重量："+weight;
	}
	public abstract void speak();
	
	public abstract void eat();
}

class Bird extends Pet{

	private int fly;
	
	public Bird(String name, int age, double weight,int fly) {
		super(name, age, weight);
		this.fly = fly;
	}
	
	public int getFly() {
		return fly;
	}

	public void setFly(int fly) {
		this.fly = fly;
	}

	

	@Override
	public void speak() {
		System.out.println("genlonggenglong");
	}

	@Override
	public void eat() {
		System.out.println("chongzi");
	}
	@Override
	public String toString() {
		return  super.toString()+",飞行："+fly;
	} 
	
	
}
class  Test{
  public static void main(String[] args) {
	  Pet p = new Bird("测试",20,50,60);
	  p.eat();
	  p.speak();//虚方法调用
	  System.out.println(p);
  }
}

抽象类中可以包括：

1. 属性
2. 构造器
3. 具体方法
4. 抽象方法