Java抽象类与接口

一 抽象类

• 不能被实例化
  • 其他该有的都能有
    • 静态代码块
    • 实例代码块
    • 构造方法
    • …
• 可以被继承
  • 多了一层 代码是否重写的校验
  • 普通类继承抽象类
    • 要重写里面所有的的继承方法
    • 可以不重写 设计为抽象类（出来混迟早要还）??
• abstract 修饰类
  • 有抽象方法的类必是抽象类
    • 抽象方法
      • abstract 修饰方法
      • 不需要具体实现
      • 不能static private final 修饰
  • 是抽象类 不一定有抽象方法

来个代码look，look~

abstract class Food{
    public abstract void draw();
}
class Hamlburg extends Food {
    @Override
    public void draw() {
        System.out.println("??");
    }
}
class Pizza extends Food {
    @Override
    public void draw() {
        System.out.println("??");
    }
}
class Drumstick extends Food {
    @Override
    public void draw() {
        System.out.println("??");
    }
}
class Cake extends Food {
    @Override
    public void draw() {
        System.out.println("??");
    }
}
class IceCream extends Food {
    @Override
    public void draw() {
        System.out.println("??");
    }
}

public class demo1  {

    public static void foodMap(Food food){
        food.draw();
    }

    public static void main(String[] args) {
        foodMap(new Hamlburg());
        foodMap(new Pizza());
        foodMap(new Drumstick());
        foodMap(new Cake());
        foodMap(new IceCream());
    }

}

• 

二 接口

• interface 类名（前I）

• 成员变量默认为

  • public static final修饰

• 成员方法默认为

  • public stract

    • 抽象方法

      • 不能具体实现

        • 普通成员方法

      • 能具体实现

        • default修饰（普通成员方法

        • 静态成员方法

• 不能实例化

• class 类 implements 接口

  • 重写接口里的方法（这次要写public）

  • 一个接口可以引用 具体实现类的（向上转型）

• 不能有静态代码块 构造方法

class Student implements Comparable<Student>{
    public String name;
    public int age;
    public double mark;

    public Student(String name, int age, double mark) {
        this.name = name;
        this.age = age;
        this.mark = mark;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + ''' +
                ", age=" + age +
                ", mark=" + mark +
                '}';
    }

    @Override
    public int compareTo(Student o) {
        return this.age-o.age;
    }
}
class AgeComparator implements Comparator<Student>{
    @Override
    public int compare(Student o1, Student o2) {
        return o1.age-o2.age;
    }
}
class MarkComparator implements Comparator<Student>{
    @Override
    public int compare(Student o1, Student o2) {
        return (int)(o1.mark-o2.mark);
    }
}
class NameComparator implements Comparator<Student>{
    @Override
    public int compare(Student o1, Student o2) {
        return o1.name.compareTo(o2.name);
    }
}


public class Text {
    public static void main(String[] args) {
        Student[] students = new Student[3];
        students[0] = new Student("balala",18,59.9);
        students[1] = new Student("abc",22,99);
        students[2] = new Student("babiq",19,66.6);

        System.out.println("排序前" +Arrays.toString(students));
        Arrays.sort(students,new MarkComparator());
        System.out.println("排序后" +Arrays.toString(students));

    }

    public static void main2(String[] args) {
        Student student1 = new Student("balala",18,59.9);
        Student student2 = new Student("acc",14,29.9);
        MarkComparator markComparator = new MarkComparator();
        int ret = markComparator.compare(student1,student2);
        System.out.println(ret);
    }

    public static void main1(String[] args) {
        Student student1 = new Student("balala",18,59.9);
        Student student2 = new Student("acc",14,29.9);
        if(student1.compareTo(student2) > 0){
            System.out.println("student1 > student2");
        }

    }
}

abstract class Animal{
    public String name;
    public int age;

    public abstract void eat();

    public Animal(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return "Animal{" +
                "name='" + name + ''' +
                ", age=" + age +
                '}';
    }
}


interface IFly{
    void fly();
}
interface ISpeak{
    void speak();
}


class Bird extends Animal implements IFly,ISpeak{
    public int wing;

    public Bird(String name, int age) {
        super(name, age);
    }

    @Override
    public void eat() {
        System.out.println(name+" 正在吃虫子~");
    }


    @Override
    public void fly() {
        System.out.println(name+" 有翅膀的鸟在飞~~");
    }

    @Override
    public void speak() {
        System.out.println(name+" 在学人说话！");
    }
}

class Dog extends Animal implements ISpeak{

    public Dog(String name, int age) {
        super(name, age);
    }

    @Override
    public void eat() {
        System.out.println(name+" 在被无情的吃狗粮");
    }


    @Override
    public void speak() {
        System.out.println(name+" 在汪汪汪的大叫！！");
    }
}

public class demo2{
    public static void speak(ISpeak iSpeak){
        iSpeak.speak();
    }

    public static void main(String[] args) {
        speak(new Dog("狗子",3));
        speak(new Bird("小鸟",2));
    }


    public static void main1(String[] args) {
        Bird bird = new Bird("lala",2);
        bird.fly();
        bird.eat();
        bird.speak();
        Dog dog = new Dog("狗子",3);
        dog.eat();
        dog.speak();
    }
}