如何从继承类的数组列表中修改项？

Question

我正在制作动物园管理系统，我可以添加动物，修改动物，删除动物和打印动物。我正在为这个项目使用一个名为ArrayList的动态数组。我的问题是我无法修改继承类中的元素。但是，我能够修改父类中的元素 这是我的父类：

public abstract class Animals {
    String name, animalID, type, food;
    int age;

    Animals(String name, String animalID, String type, String food, int age)
    {
        this.name = name;
        this.animalID = animalID;
        this.type = type;
        this.food = food;
        this.age = age;
    }

    Animals()
    {
        this ("No Name", "No Animal ID","No Type Specified","No Food Specified",-1);
    }

    public abstract String getName();
    public abstract void setName(String name);
    public abstract String getAnimalID();
    public abstract void setAnimalID(String animalID);
    public abstract String getType();
    public abstract void setType(String type);
    public abstract String getFood();
    public abstract void setFood(String food);
    public abstract int getAge();
    public abstract void setAge(int age);
    public abstract void print();
}

这是我继承的课程：

public class Birds extends Animals {
    String furColour, importLocation;
    int cageNumber;

    Birds(String name, String animalID, String type, String food, int age,String furColour, String importLocation, int cageNumber)
    {
        super(name,animalID,type,food,age);
        this.furColour = furColour;
        this.importLocation = importLocation;
        this.cageNumber = cageNumber;
    }

    Birds ()
    {
        this (null,null,null,null,0,"No Fur Colour Specified","No Import Location Specified",-1);
    }

    @Override
    public String getName() {
        return name;
    }

    @Override
    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String getAnimalID() {
        return animalID;
    }

    @Override
    public void setAnimalID(String animalID) {
        this.animalID = animalID;
    }

    @Override
    public String getType() {
        return type;
    }

    @Override
    public void setType(String type) {
        this.type = type;
    }

    @Override
    public String getFood() {
        return food;
    }

    @Override
    public void setFood(String food) {
        this.food = food;
    }

    @Override
    public int getAge() {
        return age;
    }

    @Override
    public void setAge(int age) {
        this.age = age;
    }

    public String getFurColour() {
        return furColour;
    }

    public void setFurColour(String furColour) {
        this.furColour = furColour;
    }

    public String getImportLocation() {
        return importLocation;
    }

    public void setImportLocation(String importLocation) {
        this.importLocation = importLocation;
    }

    public int getCageNumber() {
        return cageNumber;
    }

    public void setCageNumber(int cageNumber) {
        this.cageNumber = cageNumber;
    }

    @Override
    public void print()
    {
        System.out.println("Name: "+name+"\nAnimal ID: "+animalID+"\nType "+type+"\nFood: "+food+"\nAge: "+age+"\nFur Colour: "+furColour+"\nImport Location: "+importLocation+"\nCage Number: "+cageNumber+"\n");
    }
}

现在，假设特定鸟的信息已经存在于索引5的数组列表中，例如，如何修改索引为5的鸟的毛发颜色信息？

到目前为止，这是我的modify功能：

static public void modify()
    {
        System.out.print("Enter Animal ID: ");
        String modifyId = input.next();
        for (int i=0; i<zooAnimals.size(); i++)
        {
            if (zooAnimals.get(i).getAnimalID().equals(modifyId))
            {
                System.out.println("Animal Modify Menu\n------------------------------");
                String animalType = zooAnimals.get(i).getType();
                switch (animalType)
                {
                    case "Bird": modifyBird(i,modifyId);
                        break;
                    case "Monkey": modifyMonkey(i);
                        break;
                    case "Lion": modifyLion(i);
                        break;
                }
            }
            else
            {
                System.out.println("Animal Id does not exist");
            }
        }
    }

static public void modifyMenu()
{
    System.out.println("A. Change Name");
    System.out.println("B. Change ID");
    System.out.println("C. Change Food");
    System.out.println("D. Change Age");
}
static public void modifyBird(int animalIndex, String id)
{
    char birdSelect;
    boolean continueLoop = true;
    do
    {
        modifyMenu();
        System.out.println("E. Change Fur Colour");
        System.out.println("F. Change Import Location");
        System.out.println("G. Change Cage Number");
        System.out.println("H. Back to Main Menu");
        System.out.print("Choose an option: ");
        birdSelect = input.next().charAt(0);
        switch (birdSelect)
        {
            case 'a':
            case 'A': System.out.print("Enter New Name: ");
                         String newName = input.next();
                         zooAnimals.get(animalIndex).setName(newName);
                         System.out.println("Name Changed!");
                break;
            case 'b':
            case 'B': System.out.print("Enter New ID: ");
                        String newId = input.next();
                        zooAnimals.get(animalIndex).setAnimalID(newId);
                         System.out.println("ID Changed!");
                break;
            case 'c':
            case 'C': System.out.print("Enter New Food: ");
                        String newFood = input.next();
                        zooAnimals.get(animalIndex).setFood(newFood);
                         System.out.println("Food Changed!");
                break;
            case 'd':
            case 'D': System.out.print("Enter New Age: ");
                        int newAge = input.nextInt();
                        zooAnimals.get(animalIndex).setAge(newAge);
                         System.out.println("Age Changed!");
                break;
            case 'e':
            case 'E': System.out.print("Enter New Fur Colour");
                         String newColour = input.next();
                         //zooAnimals.get(animalIndex).setFurColour = newColour;
                         //How do I do this?
                break;
            case 'f':
            case 'F':
                break;
            case 'g':
            case 'G':
                break;
            case 'h':
            case 'H':
                break;
            default: System.out.println("Please choose a valid option!");
            break;
        }
    } while (continueLoop);
}

static public void modifyMonkey(int animalIndex)
{
    modifyMenu();
}

static public void modifyLion(int animalIndex)
{
    modifyMenu();
}

这是我的add函数，可以更好地理解我的代码：

static public void add()
{
    boolean continueLoop = true;
    do
    {
        System.out.println();
        System.out.println("Add Menu\n----------------");
        System.out.println("A. Add a Bird");
        System.out.println("B. Add a Monkey");
        System.out.println("C. Add a Lion");
        System.out.println("D. Back to Main Menu");
        System.out.print("Choose an Option: ");
        char animalType = input.next().charAt(0);
        System.out.println();
        if (animalType == 'd' || animalType == 'D')
        {
            System.out.println();
            menu();
        }
        else
        {
            System.out.print("Enter Animal Name: ");
            String animalName = input.next();
            System.out.print("\nEnter Animal ID: ");
            String animalId = input.next();
            System.out.print("\nEnter Animal Food: ");
            String animalFood = input.next();
            boolean isNumber;
            System.out.print("\nEnter Animal Age: ");
            do
            {
                if (input.hasNextInt())
                {
                    int animalAge = input.nextInt();
                    isNumber = true;
                    System.out.println();
                    switch (animalType)
                    {
                        case 'a':
                        case 'A': addBird(animalName,animalId,"Bird",animalFood,animalAge);
                            break;
                        case 'b':
                        case 'B': addMonkey(animalName,animalId,"Monkey",animalFood,animalAge);
                            break;
                        case 'c':
                        case 'C': addLion(animalName,animalId,"Lion",animalFood,animalAge);
                            break;
                        case 'd':
                        case 'D': menu();
                            break;
                        default: System.out.println("Please choose a valid option");
                            break;
                    }
                }
                else
                {
                    System.out.println("Invalid Input! Please Enter Again");
                    isNumber = false;
                    input.next();
                }
            } while (!(isNumber));
         }  
    } while (continueLoop);
}

static public void addBird(String name, String animalID, String type, String food, int age)
{
    Animals b;
    System.out.print("Enter Bird's Fur Colour: ");
    String birdColour = input.next();
    System.out.print("\nEnter Bird's Imported Location: ");
    String birdLoc = input.next();
    System.out.print("\nEnter Bird's Cage Number: ");
    boolean isNumber;
    do
    {
        if (input.hasNextInt())
        {
            int birdCageNum = input.nextInt();
            isNumber = true;
            b = new Birds(name,animalID,type,food,age,birdColour,birdLoc,birdCageNum);
            zooAnimals.add(b);
        }
        else
        {
            System.out.println("Enter an Integer Number!\nEnter again: ");
            isNumber = false;
            input.next();
        }
    } while (!(isNumber));
}

static public void addMonkey(String name, String animalID, String type,String food, int age)
{
    Animals m;
    System.out.print("Enter Monkey's Behaviour (Wild, Normal, Calm): ");
    String behaviour = input.next();
    System.out.print("\nEnter Number of Offsprings: ");
    boolean isNumber;
    do
    {
        if (input.hasNextInt())
        {
            int offsprtingNum = input.nextInt();
            isNumber = true;
            m = new Monkey(name,animalID,type,food,age,behaviour,offsprtingNum);
            zooAnimals.add(m);
        }
        else
        {
            System.out.println("Enter an Integer Number!\nEnter again: ");
            isNumber = false;
            input.next();
        }
    } while (!(isNumber));
}

static public void addLion(String name, String animalID, String type,String food, int age)
{
    Animals l;
    System.out.print("Enter Lion's Health (Strong, Normal, Weak): ");
    String health = input.next();
    System.out.print("Enter Number of Meats eaten: ");
    boolean isNumber;
    do
    {
        if (input.hasNextInt())
        {
            int meatNumber = input.nextInt();
            isNumber = true;
            l = new Lion(name, animalID, type, food,age,health, meatNumber);
            zooAnimals.add(l);
        }
        else
        {
            System.out.print("\nInvalid Input!\nEnter Again:");
            isNumber = false;
            input.next();
        }
    } while (!(isNumber));
}

Answer 1

听起来您ArrayList的类型为Animals，并且您希望在Birds类上定义的某个元素上调用方法。检索元素后，只需将其强制转换为Birds类型，然后调用相关方法：

((Birds) zooAnimals.get(animalIndex)).setFurColour(newColour);

Casting只是告诉编译器对象的底层类型是什么，以便您可以访问该类型的方法。 inheritance上的官方Java教程详细介绍了类型转换的工作原理。

顺便说一下，作为惯例，你的班级名称通常应该是单数（Bird，Animal），而不是复数。