抽象类

final修饰的类，不能有子类。
abstract修饰的类，不能实例化。
不能用abstract修饰私有方法、静态方法、final的方法、final的类。

私有方法不能重写
避免静态方法使用类进行调用
final的方法不能被重写
final修饰的类不能有子类

示例1

航运公司系统，Vehicle类

java">public abstract class Vehicle{
    public abstract double calcFuelEfficiency();
    public abstract double calcTripDistance();
}

public class Truck extends Vehicle{
    public double calcFuelEfficiency();
    public double calcTripDistance();
}

public class RiverBarge extends Vehicle{
    public double calcFuelEfficiency();
    public double calcTripDistance();
}

示例2

GeometricObject

java">public abstract class GeometricObject {
    String color;

    double weight;

    public GeometricObject(String color, double weight) {
        this.color = color;
        this.weight = weight;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public double getWeight() {
        return weight;
    }

    public void setWeight(double weight) {
        this.weight = weight;
    }

    public abstract double findArea();
}

Circle

java">public class Circle extends GeometricObject{
    private double radius;
    public Circle(double radius, String color, double weight){
        super(color, weight);
        this.radius = radius;
    }

    public double getRadius() {
        return radius;
    }

    public void setRadius(double radius) {
        this.radius = radius;
    }

    @Override
    public double findArea(){
        return 3.14 * radius * radius;
    }
}

Rectangle

java">public class Rectangle extends GeometricObject{
    private double width;

    private double height;

    public Rectangle(String color, double weight, double width, double height) {
        super(color, weight);
        this.width = width;
        this.height = height;
    }

    public double getWidth() {
        return width;
    }

    public void setWidth(double width) {
        this.width = width;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    @Override
    public double findArea() {
        return width * height;
    }
}

GeometricTest

java">public class GeometricTest {
    public static void main(String[] args) {
        // 抽象类不能创建实例
        Circle circle = new Circle(2.0, "Blue", 3.0);
        System.out.println(circle.findArea());

        Rectangle rectangle = new Rectangle("red", 3.0, 3.0, 4.0);
        System.out.println(rectangle.findArea());
        
    }
}

模板方法设计模式

java">public class TemplateMethodTest {
    public static void main(String[] args) {
        BankTemplateMethod drawMoney = new DrawMoney();
        drawMoney.process();

        System.out.println();

        BankTemplateMethod btm = new ManageMoney();
        btm.process();
    }
}

// 创建抽象类
abstract class BankTemplateMethod{
    public void takeNumber() {
        System.out.println("取号排队");
    }

    public abstract void transact(); // 办理具体业务

    public void evaluate() {
        System.out.println("反馈评分");
    }

    // 模板方法，把基本操作组合到一起
    public final void process() {
        this.takeNumber();
        this.transact();
        this.evaluate();
    }
}


// 子类
class DrawMoney extends BankTemplateMethod {

    @Override
    public void transact() {
        System.out.println("我要取款");
    }
}

class ManageMoney extends BankTemplateMethod{

    @Override
    public void transact() {
        System.out.println("我要理财");
    }
}