Java面向对象之继承和重写

继承和重写

今天学习了继承与继承中的重写方法，并且做了小例子，主要是运用了JAVA的一些基本知识，主要是继承和方法的改写，还用到了之前的排序方法。这个小程序是描述了对于化妆品的进货（添加化妆品的种类或者和数量）以及展示现有的化妆品种类以及价格（价格按照从小到大排序）。

1. 首先是建立一个化妆品类和一个化妆品管理类，在管理化妆品类中，如果空间不够就要进行空间的扩展

//化妆品类class CosmeticType {    private String name;    private float price;    private String type;        public CosmeticType(String name, float price, String type) {        super();        this.name = name;        this.price = price;        this.type = type;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public float getPrice() {        return price;    }    public void setPrice(float price) {        this.price = price;    }    public String getType() {        return type;    }    public void setType(String type) {        this.type = type;    }    //得到化妆品信息    public String getInfo(){        return "The name of Cosmetic is " + name + "     price is " + price + "     The type is " + type;    }}//化妆品管理类class CosmeticManager{    //protected 才可以继承    protected CosmeticType[] cosmetics = new CosmeticType[4];    protected int count = 0;    //化妆品进货    public void add(CosmeticType cos){        //如果长度不够就扩展空间        if(count > cosmetics.length){            //将空间增加一半            int newLen = cosmetics.length*3/2+1;            //将原来的信息复制到新的空间中            cosmetics = Arrays.copyOf(cosmetics, newLen);        }        //将添加的cos(一个cosmetic对象)赋值给 最后一个位置        cosmetics[count] = cos;        count++;    }    //输出所有化妆品    public void printInfo(){        for(int i = 0; i < count; i++){            System.out.println(cosmetics[i].getInfo());        }    }}

2 . 测试输出一下所有的化妆品

public class Cosmetic{    public static void main(String[] srgs){        CosmeticManager cm = new CosmeticManager();        cm.add(new CosmeticType("大宝", 8.0f, "China"));          cm.add(new CosmeticType("Olay", 260.0f, "America"));        cm.add(new CosmeticType("郁美净", 12.0f, "China"));        cm.add(new CosmeticType("Lancome", 450.0f, "France"));              cm.printInfo();    }}

基本的类已经构造完成，也可以输出，接下来进行继承和改写部分，在继承时，要确保父类中的属性和方法是protected或者是public，只有这样才能被子类继承。

1.首先写一个继承化妆品管理类的子类，来实现将化妆品按价格从小到大输出

class SortCosmeticManager extends CosmeticManager{    //重写了父类的打印方法，实现了排序    public void printInfo(){        CosmeticType[] cs = new CosmeticType[super.count];        for(int i = 0; i < cs.length; i++){            cs[i] = super.cosmetics[i];        }        CosmeticType temp = null;        for(int i = 0; i < cs.length-1; i++){            for(int j = 0; j < cs.length-1-i; j++){                if(cs[j].getPrice() >cs[j+1].getPrice()){                    temp = cs[j];                    cs[j] = cs[j+1];                    cs[j+1] = temp;                         }            }        }    for(int i = 0; i < count; i++){        System.out.println(cs[i].getInfo());        }    }}

2.测试按价格输出化妆品

public class Cosmetic{    public static void main(String[] srgs){        SortCosmeticManager cm = new SortCosmeticManager();        cm.add(new CosmeticType("大宝", 8.0f, "China"));          cm.add(new CosmeticType("Olay", 260.0f, "America"));        cm.add(new CosmeticType("郁美净", 12.0f, "China"));        cm.add(new CosmeticType("Lancome", 450.0f, "France"));              cm.printInfo();    }}

3.然后再写一个继承化妆品管理类的子类，实现只输出国产化妆品

//只输出国产化妆品class ImportCosmeticManager extends CosmeticManager{    public void printInfo(){        for(int i = 0; i < super.count; i++){            if("China".equals(super.cosmetics[i].getType())){                System.out.println(cosmetics[i].getInfo());            }        }    }}

4.测试输出国产化妆品

public class Cosmetic{    public static void main(String[] srgs){        ImportCosmeticManager cm = new ImportCosmeticManager();        cm.add(new CosmeticType("大宝", 8.0f, "China"));          cm.add(new CosmeticType("Olay", 260.0f, "America"));        cm.add(new CosmeticType("郁美净", 12.0f, "China"));        cm.add(new CosmeticType("Lancome", 450.0f, "France"));              cm.printInfo();    }}

程序到此结束，所有的功能都已实现。