30、静态内部类

静态内部类是在一个类中定义类。（public static class 内部类）
好处是：

1. 减少类的可见性，减少Java source源文件的数量，让相关的类都集中在一个文件里
2. 在内部类里访问外部类的属性（private属性）
3. 外部的类可以访问内部的类，内部的类也可以外部类的属性。

代码示例：

package day16;

public class PhoneV2 extends MerchandiseWithConstructor{
    private double screenSize;
    private CPU cpu;
    private double memoryG;
    private double storageG;
    private String brand;
    protected String os;
    //  给手机品类增加个数限制
    private static int MAX_BUY_COUNT = 5;


    public PhoneV2(int id, String name, int count, double soldPrice, double purchasingRrice,
                   double screenSize, double memoryG, double storageG, String brand, String os) {
//      因为父类的属性不是公开的需要set方法来进行设置

        super(id,name,count,soldPrice,purchasingRrice);


        this.screenSize = screenSize;
        this.memoryG = memoryG;
        this.storageG = storageG;
        this.brand = brand;
        this.os = os;

    }


    public static class CPU {
        private double speed;
        private String producer;

        public CPU(double speed, String producer) {
            this.speed = speed;
            this.producer = producer;
        }


        public double getSpeed() {
//          内部类和这个类本身的访问情况是一样的，可以访问外部类的private属性
//            PhoneV2 ph = null;
//            ph.memoryG = 99;
            return speed;
        }

        public void setSpeed(double speed) {
            this.speed = speed;
        }

        public String getProducer() {
            return producer;
        }

        public void setProducer(String producer) {
            this.producer = producer;
        }
    }



//  单独实现子类对于购买数量的限制
//  在子类中声明同样的方法（返回值、方法名、入参）

    public double buy(int count) {
        if (count > MAX_BUY_COUNT) {
            System.out.println("超出商品的单词购买上限，购买失败");
            return -1;
        }

        return super.buy(count);
    }
    public void describe() {
        super.describe();
        System.out.println("手机配置信息如下：\n屏幕大小：" + this.screenSize + "英寸 \n" + " \n内存大小：" + this.memoryG + "G \n存储空间：" + storageG + "G \n品牌：" + this.brand + " \n操作系统：" + os);
    }

    public double getScreenSize() {
        return screenSize;
    }

    public void setScreenSize(double screenSize) {
        this.screenSize = screenSize;
    }

    public double getMemoryG() {
        return memoryG;
    }

    public void setMemoryG(double memoryG) {
        this.memoryG = memoryG;
    }

    public double getStorageG() {
        return storageG;
    }

    public void setStorageG(double storageG) {
        this.storageG = storageG;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public String getOs() {
        return os;
    }

    public void setOs(String os) {
        this.os = os;
    }


}

测试代码：

package day16;

public class TestPhoneV2 {
    public static void main(String[] args) {
        PhoneV2 v2 = new PhoneV2(200,"小米10",200,3999,3599,6,8.0,128.0,"小米","Android");

        v2.describe();


        PhoneV2.CPU cpu = new PhoneV2.CPU(5.5, "intel");

        System.out.println(cpu.getProducer());
        System.out.println(cpu.getSpeed());



    }
}

运行结果：

image.png

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除了静态内部类，还有成员内部类，局部内部类，由于使用的比较少，这里不再进行赘述。等需要用到的时候再去了解。