Java 中抽象类和接口的区别
正如我们所知，抽象是指隐藏特性的内部实现，并且只向用户显示功能。即它的工作原理(显示)、工作原理(隐藏)。抽象类和接口都用于抽象，因此接口和抽象类是必需的先决条件
抽象类 vs 接口
- 方法类型:接口只能有抽象方法。抽象类可以有抽象和非抽象方法。从 Java 8 开始，它也可以有默认和静态方法。
- 最终变量:Java 接口中声明的变量默认为最终变量。抽象类可能包含非最终变量。
- 变量类型:抽象类可以有 final、non-final、static 和 non-static 变量。接口只有静态变量和最终变量。
- 实现:抽象类可以提供接口的实现。接口不能提供抽象类的实现。
- 继承 vs 抽象:一个 Java 接口可以用关键字“implements”实现，一个抽象类可以用关键字“extends”扩展。
- 多个实现:一个接口只能扩展另一个 Java 接口，一个抽象类可以扩展另一个 Java 类，实现多个 Java 接口。
- 数据成员的可访问性:默认情况下，Java 接口的成员是公共的。Java 抽象类可以有私有、受保护等类成员。
例 1-A:
Java 语言(一种计算机语言，尤用于创建网站)
// Java Program to Illustrate Concept of
// Abstract Class
// Importing required classes
import java.io.*;
// Class 1
// Helper abstract class
abstract class Shape {
// Declare fields
String objectName = " ";
// Constructor of this class
Shape(String name) { this.objectName = name; }
// Method
// Non-abstract methods
// Having as default implementation
public void moveTo(int x, int y)
{
System.out.println(this.objectName + " "
+ "has been moved to"
+ " x = " + x + " and y = " + y);
}
// Method 2
// Abstract methods which will be
// implemented by its subclass(es)
abstract public double area();
abstract public void draw();
}
// Class 2
// Helper class extending Class 1
class Rectangle extends Shape {
// Atributes of rectangle
int length, width;
// Constructor
Rectangle(int length, int width, String name)
{
// Super keyword refers to current instance itself
super(name);
// this keyword refers to current instance itself
this.length = length;
this.width = width;
}
// Method 1
// To draw rectangle
@Override public void draw()
{
System.out.println("Rectangle has been drawn ");
}
// Method 2
// To compute rectangle area
@Override public double area()
{
// Length * Breadth
return (double)(length * width);
}
}
// Class 3
// Helper class extending Class 1
class Circle extends Shape {
// Attributes of a Circle
double pi = 3.14;
int radius;
// Constructor
Circle(int radius, String name)
{
// Super keyword refers to parent class
super(name);
// This keyword refers to current instance itself
this.radius = radius;
}
// Method 1
// To draw circle
@Override public void draw()
{
// Print statement
System.out.println("Circle has been drawn ");
}
// Method 2
// To compute circle area
@Override public double area()
{
return (double)((pi * radius * radius));
}
}
// Class 4
// Main class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating the Object of Rectangle class
// and using shape class reference.
Shape rect = new Rectangle(2, 3, "Rectangle");
System.out.println("Area of rectangle: "
+ rect.area());
rect.moveTo(1, 2);
System.out.println(" ");
// Creating the Objects of circle class
Shape circle = new Circle(2, "Circle");
System.out.println("Area of circle: "
+ circle.area());
circle.moveTo(2, 4);
}
}
Output
Area of rectangle: 6.0
Rectangle has been moved to x = 1 and y = 2
Area of circle: 12.56
Circle has been moved to x = 2 and y = 4
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