java抽象(abstract)和接口（interface）

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我是靠谱客的博主紧张白云，这篇文章主要介绍java抽象(abstract)和接口（interface），现在分享给大家，希望可以做个参考。

一：抽象

（1）只是一个方法签名，没有方法体

abstract void setPages(int page);

（2）如果一个类有了一个抽象方法，这个类就必须声明为抽象类；如果父类是抽象类，子类必须覆盖所有在父类的抽象方法，否则子类也将成为一个抽象类

比如下面的例子，父类的四个方法都必须在子类中实现

（3）可以调用父类的成员变量

比如可以用this.pages=pages

复制代码

package practice3;
abstract class Books{
	int pages;
	int prices;
	abstract void setPages(int page);
	abstract void setPrices(int price);
	abstract int getPages();
	abstract double getPrices();
}
class story extends Books{
	@Override
	void setPages(int page) {
		// TODO Auto-generated method stub
		this.pages=page;
	}
	@Override
	void setPrices(int price) {
		// TODO Auto-generated method stub
		this.prices=price;
	}
	@Override
	int getPages() {
		// TODO Auto-generated method stub
		return pages;
	}
	@Override
	double getPrices() {
		// TODO Auto-generated method stub
		return prices;
	}
}
class magzine extends Books{
	@Override
	void setPages(int page) {
		// TODO Auto-generated method stub
		this.pages=page;
	}
	@Override
	void setPrices(int price) {
		// TODO Auto-generated method stub
		this.prices=price;
	}
	@Override
	int getPages() {
		// TODO Auto-generated method stub
		return pages;
	}
	@Override
	double getPrices() {
		// TODO Auto-generated method stub
		return prices;
	}
}
public class test1 {
   public static void main(String[] args) {
	  story s=new story();
	  s.setPages(100);
	  s.setPrices(20);
	  System.out.println(s.getPages());
	  System.out.println(s.getPrices());
	  magzine m=new magzine();
	  m.setPages(102);
	  m.setPrices(203);
	  System.out.println(m.getPages());
	  System.out.println(m.getPrices());
}
}

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package practice3;
abstract class Books{
	int pages;
	int prices;
	abstract void setPages(int page);
	abstract void setPrices(int price);
	abstract int getPages();
	abstract double getPrices();
}
class story extends Books{
	@Override
	void setPages(int page) {
		// TODO Auto-generated method stub
		this.pages=page;
	}
	@Override
	void setPrices(int price) {
		// TODO Auto-generated method stub
		this.prices=price;
	}
	@Override
	int getPages() {
		// TODO Auto-generated method stub
		return pages;
	}
	@Override
	double getPrices() {
		// TODO Auto-generated method stub
		return prices;
	}
}
class magzine extends Books{
	@Override
	void setPages(int page) {
		// TODO Auto-generated method stub
		this.pages=page;
	}
	@Override
	void setPrices(int price) {
		// TODO Auto-generated method stub
		this.prices=price;
	}
	@Override
	int getPages() {
		// TODO Auto-generated method stub
		return pages;
	}
	@Override
	double getPrices() {
		// TODO Auto-generated method stub
		return prices;
	}
}
public class test1 {
   public static void main(String[] args) {
	  story s=new story();
	  s.setPages(100);
	  s.setPrices(20);
	  System.out.println(s.getPages());
	  System.out.println(s.getPrices());
	  magzine m=new magzine();
	  m.setPages(102);
	  m.setPrices(203);
	  System.out.println(m.getPages());
	  System.out.println(m.getPrices());
}
}

二：接口

（1）接口其实就是完全抽象的类

（2）接口所有的方法都没有方法体

默认的：

方法：public abstract

成员变量：public static final

（3）接口中的变量都必须初始化

（4）使用接口的类必须实现接口中的所有方法（类型：public）

复制代码

package practice3;
interface Books{
	int pages=0;
	int prices=0;
	public void setPages(int page);
	public void setPrices(int price);
	public int getPages();
	public double getPrices();
}
class story implements Books{
	int pages,prices;
	public void setPages(int page) {
		// TODO Auto-generated method stub
		this.pages=page;
	}
	public void setPrices(int price) {
		// TODO Auto-generated method stub
		this.prices=price;
	}
	public int getPages() {
		// TODO Auto-generated method stub
		return pages;
	}
	public double getPrices() {
		// TODO Auto-generated method stub
		return prices;
	}
}
class magzine implements Books{
	int pages,prices;
	public void setPages(int page) {
		// TODO Auto-generated method stub
		this.pages=page;
	}
	@Override
	public void setPrices(int price) {
		// TODO Auto-generated method stub
		this.prices=price;
	}
	@Override
	public int getPages() {
		// TODO Auto-generated method stub
		return pages;
	}
	@Override
	public double getPrices() {
		// TODO Auto-generated method stub
		return prices;
	}
}
public class test1 {
   public static void main(String[] args) {
	  story s=new story();
	  s.setPages(100);
	  s.setPrices(20);
	  System.out.println(s.getPages());
	  System.out.println(s.getPrices());
	  magzine m=new magzine();
	  m.setPages(102);
	  m.setPrices(203);
	  System.out.println(m.getPages());
	  System.out.println(m.getPrices());
}
}

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package practice3;
interface Books{
	int pages=0;
	int prices=0;
	public void setPages(int page);
	public void setPrices(int price);
	public int getPages();
	public double getPrices();
}
class story implements Books{
	int pages,prices;
	public void setPages(int page) {
		// TODO Auto-generated method stub
		this.pages=page;
	}
	public void setPrices(int price) {
		// TODO Auto-generated method stub
		this.prices=price;
	}
	public int getPages() {
		// TODO Auto-generated method stub
		return pages;
	}
	public double getPrices() {
		// TODO Auto-generated method stub
		return prices;
	}
}
class magzine implements Books{
	int pages,prices;
	public void setPages(int page) {
		// TODO Auto-generated method stub
		this.pages=page;
	}
	@Override
	public void setPrices(int price) {
		// TODO Auto-generated method stub
		this.prices=price;
	}
	@Override
	public int getPages() {
		// TODO Auto-generated method stub
		return pages;
	}
	@Override
	public double getPrices() {
		// TODO Auto-generated method stub
		return prices;
	}
}
public class test1 {
   public static void main(String[] args) {
	  story s=new story();
	  s.setPages(100);
	  s.setPrices(20);
	  System.out.println(s.getPages());
	  System.out.println(s.getPrices());
	  magzine m=new magzine();
	  m.setPages(102);
	  m.setPrices(203);
	  System.out.println(m.getPages());
	  System.out.println(m.getPrices());
}
}