“商苑面馆：Java类的继承”的版本间的差异

2019年5月20日 (一) 14:07的最新版本

核心知识点=

• 继承就是子类继承父类的特征和行为，使得代码能够复用；
• 声明继承之后，子类就可以使用父类所有的变量和方法；
• 如果有变量和方法父类当中不存在，子类可以自己定义。

步骤

定义一个父类

定义一个父类，并把子类当中公共的属性和方法定义到里面：

Food类：

package entity;

public class Food {
	//成员变量
	//名称
	private String name;
	//价格
	private double price;
	//数量
	private int num;
	
	/*构造方法*/
	public Food(){
		
	}
	public Food(String name,double price,int num){
		this.name = name;
		this.price = price;
		this.num = num;
	}
	
	//成员方法
	public String getName(){
		return this.name;
	}
	public double getPrice(){
		return this.price;
	}
	public int getNum(){
		return this.num;
	}
	//写方法
	public boolean setName(String s){
		this.name = s;
		return true;
	}
	public boolean setPrice(double p){
	    this.price = p;
	    return true;
	}
	public boolean setNum(int n){
	    this.num = n;
	    return true;
	}
	   
	public String toString(){
	    return "名称:" +this.name+"价格："+
	               this.price + "剩余数量: " + this.num;
	}

	public static void main(String[] args) {
		
		Food f0 = new Food("炸酱面",12,3);
		System.out.println(f0.toString());
		

	}
	

}

子类增添extends关键字

public class Noodle extends Food {
...
}

写子类的构造方法

子类构造方法 ，调用父类的构造方法。

public class Noodle extends Food {
	private double weight;//份量
	/*构造方法*/
	public Noodle(){
		
	}
	public Noodle(String name,double price,int num){
		super(name,price,num);
	}

编写子类里面独有的成员和方法

面条类：

public class Noodle extends Food {
	private double weight;//份量
	/*构造方法*/
	public Noodle(){
		
	}
	public Noodle(String name,double price,int num){
		super(name,price,num);
	}
        //增添新变量后，新的构造方法
	public Noodle(String name,double price,int num,double weight){
		super(name,price,num);
                this.weight = weight;
	}
 
        public void getWeight(){
           return this.weight;
           
}
	
}

main方法里验证

在Noodle类里main方法里写代码，对刚才的编码进行验证。

思考题：

• 怎样用带参的构造方法创建对象？

public static void main(String[] args) {
		// TODO Auto-generated method stub
		        
        Noodle n2 = new Noodle("炸酱面",12,3,500);
        System.out.println("您订的面是"+n2.getName());
        System.out.println("份量:"+n2.getWeight());

        
       
        
	}

父类和子类的完整代码

Food类：

package entity;

public class Food {
	//成员变量
	//名称
	private String name;
	//价格
	private double price;
	//数量
	private int num;
	
	/*构造方法*/
	public Food(){
		
	}
	public Food(String name,double price,int num){
		this.name = name;
		this.price = price;
		this.num = num;
	}
	
	//成员方法
	public String getName(){
		return this.name;
	}
	public double getPrice(){
		return this.price;
	}
	public int getNum(){
		return this.num;
	}
	//写方法
	public boolean setName(String s){
		this.name = s;
		return true;
	}
	public boolean setPrice(double p){
	    this.price = p;
	    return true;
	}
	public boolean setNum(int n){
	    this.num = n;
	    return true;
	}
	   
	public String toString(){
	    return "名称:" +this.name+"价格："+
	               this.price + "剩余数量: " + this.num;
	}

	public static void main(String[] args) {
		
		Food f0 = new Food("炸酱面",12,3);
		System.out.println(f0.toString());
		

	}
	

}

子类：面条类：

public class Noodle extends Food {
	private double weight;//份量
	/*构造方法*/
	public Noodle(){
		
	}
	public Noodle(String name,double price,int num){
		super(name,price,num);
	}
        //增添新变量后，新的构造方法
	public Noodle(String name,double price,int num,double weight){
		super(name,price,num);
                this.weight = weight;
	}
 
        public void getWeight(){
           return this.weight;

           
}

public static void main(String[] args) {
		// TODO Auto-generated method stub
		        
        Noodle n2 = new Noodle("炸酱面",12,3,500);
        System.out.println("您订的面是"+n2.getName());
        System.out.println("份量:"+n2.getWeight());

        
       
        
	}
	
}

</nowiki>

子类：小吃类:

public class SmallEat extends Food{

    private String flavor;
    SmallEat(){
    	
    }
    SmallEat(String name,double price,int num){
    	super(name,price,num);
    }
public String toString(){
	    return "名称:" + getName()+"价格："+
	               getPrice() + "数量: " + getNum() + "口味："+ flavor;
	}
	public static void main(String[] args) {
		// TODO Auto-generated method stub
        SmallEat s = new SmallEat("鹌鹑蛋",3,2);
        System.out.println(s.toString());
	}

}