抽象

- 日理万妓 2022-07-18 16:58 109阅读 0赞

**抽象类**：对现实世界一种类型的多种实体的统一抽象定义。  
**具体类**：一种实体的抽象描述。  
具体类再抽象就是抽象类。

> 抽象类：某些方法的实现因为子类的不同而不同，故可以在父类中声明抽象方法，交由子类具体实现这些方法。

**抽象类**：  
1.使用abstract修饰  
2.子类必须重写全部抽象方法(实现)，若是部分没有实现就还是抽象类。  
3.抽象方法必须在抽象类中  
4.抽象方法只有方法的声明，没有方法的实现，最后以;结束  
5.抽象类不能被实例化  
6.不能用abstract修饰属性，私有方法，构造器，静态方法，final方法

**抽象类比普通类多一个抽象方法(普通类具有的其他东西它都有)**

抽象类代码练习：

public abstract class Pet {
    
        private String name;
        private int age;
        private double weight;
    
        public Pet() {}
        public Pet(String name, int age, double weight) {
            this.name = name;
            this.age = age;
            this.weight = weight;
        }
    
        public void setName(String name) {
            this.name = name;
        }
        public String getName() {
            return name;
        }
    
        public void setAge(int age) {
            this.age = age;
        }
        public int getAge() {
            return age;
        }
    
        public void setWeight(double weight) {
            this.weight = weight;
        }
        public double getWeight() {
            return weight;
        }
    
        @Override
        public String toString() {
            return "昵称:" + name + ",年龄:" + age + ",体重:" + weight;
        }
        //抽象方法
        public abstract void speak();
        public abstract void eat();
    }

public class Bird extends Pet {
        
    
        private int flySpeed;
    
        public Bird() {}
        public Bird(String name, int age, double weight, int flySpeed) {
            super(name, age, weight);
            this.flySpeed = flySpeed;
        }
    
        public void setFlySpeed(int flySpeed) {
            this.flySpeed = flySpeed;
        }
        public int getFlySpeed() {
            return flySpeed;
        }
    
        @Override
        public String toString() {
            return super.toString() + ",飞行速度:" + flySpeed;
        }
    
        //实现抽象方法
        @Override
        public void speak() {
            System.out.println("吱吱吱......");
        }
        @Override
        public void eat() {
            System.out.println("吃虫子......");
        }
    
    }

public class Dog extends Pet {
        
    
        private String type;
    
        public Dog() {}
        public Dog(String name, int age, double weight, String type) {
            super(name, age, weight);
            this.type = type;
        }
    
        public void setType(String type) {
            this.type = type;
        }
        public String getType() {
            return type;
        }
    
        @Override
        public String toString() {
            return super.toString() + ",品种:" + type;
        }
    
        @Override
        public void speak() {
            System.out.println("汪汪汪...");
        }
    
        @Override
        public void eat() {
            System.out.println("吃骨头...");
        }
    }

public class Cat extends Pet {
        
    
        private String color;
    
        public Cat() {}
        public Cat(String name, int age, double weight, String color) {
            super(name, age, weight);
            this.color = color;
        }
    
        public void setColor(String color) {
            this.color = color;
        }
        public String getColor() {
            return color;
        }
    
        @Override
        public String toString() {
            return super.toString() + ",颜色:" + color;
        }
    
        @Override
        public void speak() {
            System.out.println("喵喵喵...");
        }
    
        @Override
        public void eat() {
            System.out.println("吃鱼...");
        }
    }

public class PetTest {
    
        public static void main(String[] args) {
    
            Pet[] p = new Pet[6];
            //String name, int age, double weight, String color
            //String type
            //int flySpeed
            p[0] = new Cat("小花", 2, 3.5, "花色");
            p[1] = new Cat("小黑", 1, 2.7, "黑色");
            p[2] = new Dog("大黑", 3, 20, "哈士奇");
            p[3] = new Dog("大黄", 5, 40, "家狗");
            p[4] = new Bird("咕咕", 1, 1, 20);
            p[5] = new Bird("唧唧", 1, 0.5, 30);
    
            for(int i = 0; i < p.length - 1; i++) {
    
                for(int j = 0; j < p.length - 1 - i; j++) {
    
                    if (p[j].getWeight() < p[j + 1].getWeight()) {
    
                        Pet temp = p[j];
                        p[j] = p[j + 1];
                        p[j + 1] = temp;
                    }
                }
            }
    
            for(Pet pv : p) {
                System.out.println(pv);
            }
        }
    }

**加油！**